Localization of Disulfide Bonds in the Frizzled Module of Ror1 Receptor Tyrosine Kinase*

Emoke RoszmuszDagger , András Patthy§, Mária TrexlerDagger , and László PatthyDagger

From the Dagger  Institute of Enzymology, Biological Research Center, Hungarian Academy of Sciences, Budapest, P. O. Box 7, H-1518, Hungary and § Agricultural Biotechnology Center, Gödöllo, P. O. Box 170, H-2100, Hungary

Received for publication, January 5, 2001, and in revised form, February 21, 2001


    ABSTRACT
TOP
ABSTRACT
INTRODUCTION
EXPERIMENTAL PROCEDURES
RESULTS AND DISCUSSION
REFERENCES

The frizzled (FRZ) module is a novel module type that was first identified in G-protein-coupled receptors of the frizzled and smoothened families and has since been shown to be present in several secreted frizzled-related proteins, in some modular proteases, in collagen XVIII, and in various receptor tyrosine kinases of the Ror family. The FRZ modules constitute the extracellular ligand-binding region of frizzled receptors and are known to mediate signals of WNT family members through these receptors. With an eye toward defining the structure of this important module family, we have expressed the FRZ domain of rat Ror1 receptor tyrosine kinase in Pichia pastoris. By proteolytic digestion and amino acid sequencing the disulfide bonds were found to connect the 10 conserved cysteines in a 1-5, 2-4, 3-8, 6-10, and 7-9 pattern. Circular dichroism and differential scanning calorimetry studies on the recombinant protein indicate that the disulfide-bonded FRZ module corresponds to a single, compact, and remarkably stable folding domain possessing both alpha -helices and beta -strands.


    INTRODUCTION
TOP
ABSTRACT
INTRODUCTION
EXPERIMENTAL PROCEDURES
RESULTS AND DISCUSSION
REFERENCES

Genes of the frizzled receptor family encode seven-transmembrane proteins that act as receptors for secreted Wnt glycoproteins (1). The extracellular regions of these receptors consist of about 120 residues containing 10 highly conserved cysteines. The extracellular cysteine-rich domain has been shown to be necessary and sufficient for Wnt ligand binding by frizzled receptors (2). Recently, several groups have shown independently that related domains (hereafter called FRZ1 modules for frizzled-related modules) are found in diverse modular proteins from Caenorhabditis elegans and Drosophila melanogaster to vertebrates (3-6). In addition to frizzled receptors and the related seven-transmembrane smoothened receptors, these modular proteins include secreted frizzled-related proteins, carboxypeptidase Z, collagen alpha 1 XVIII, the serine protease lipoprotein receptor-related protein 4 (7), and several members of the Ror subfamily of receptor tyrosine kinases (Fig. 1).


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Fig. 1.   Modular architecture of selected proteins containing the FRZ module. The boxes representing domains are drawn to scale. The abbreviations of domains are: IG, immunoglobulin module; FRZ, FRZ module; K, kringle module; NTR, NTR module; LDL, LDL receptor type A module; SC, scavenger receptor module; CARBOXYPEPTIDASE, carboxypeptidase domain; TYRKIN, tyrosine kinase domain; SERPRO, serine protease domain; 7TM, seven-transmembrane domain. The black bars represent signal peptides, and the vertical black bar indicates the single-transmembrane segment of receptor tyrosine kinases.

Different members of the Ror family fulfill diverse biological functions. The muscle-specific tyrosine kinase (MuSK) has been shown to be indispensable for the formation of the neuromuscular junction because it is part of a receptor complex that mediates the action of agrin (8-10). The Drosophila proteins Dror and Dnrk have been implicated in the development of the nervous system because during embryonic development expression of these proteins is restricted to neuronal tissues (11, 12). A more general role is suggested for the C. elegans Ror homologue, cam-1, which has been shown to guide migrating cells and orient the polarity of asymmetric cell divisions and axon outgrowth (13).

Recent studies suggest that vertebrate Ror1s and Ror2s may have distinct biological roles. Oishi et al. (14) have shown that during embryogenesis, expression of Rorl is sustained in the nervous system and is also detected in non-neuronal tissues after birth. In contrast, the expression of Ror2 declines after birth. Takeuchi et al. (15) have demonstrated that mouse Ror2 receptor tyrosine kinase is primarily involved in heart development and limb formation: mice with a homozygous mutation in mouse Ror2 died just after birth, exhibiting dwarfism, severe cyanosis, and short limbs and tails. Consistent with these results, DeChiara et al. (16) have shown that Ror2 is required for cartilage and growth plate development. Disruption of mouse Ror2 leads to profound skeletal abnormalities, with essentially all endochondrally derived bones foreshortened. The important role of Ror2 in skeletal patterning is also supported by the results of Oldridge et al. (17). These authors have demonstrated that brachydactyly type B in humans is caused by dominant mutations in the Ror2 gene. Recessive mutations of the gene encoding the human ROR2 tyrosine kinase were found to cause Robinow syndrome, a short-limbed dwarfism with cardiac malformations (18, 19).

The extracellular domains of the different members of the Ror family of receptor tyrosine kinases have quite different domain organizations. The extracellular regions of Ror1 and Ror2 receptor tyrosine kinases of vertebrates (20) and the C. elegans homologue, cam-1 (13), consist of an immunoglobulin-like domain at the amino terminus and a FRZ domain and kringle domain just amino-terminal to the transmembrane segment (Fig. 1). In the case of two Drosophila homologues, Dror and Dnrk, both the FRZ and kringle domains are present, but they are devoid of immunoglobulin-like domains (11, 12). In the case of MuSK, the receptor tyrosine kinase involved in neuromuscular junction formation (21), the extracellular region contains three immunoglobulin-like domains and a FRZ domain, but no kringle domain (Fig. 1). It is thus noteworthy that the only domain type common to all members of the Ror family of receptor tyrosine kinases is the FRZ module, suggesting a critical functional role for this domain type.

There is experimental evidence consistent with the importance of the FRZ modules of various Ror-type receptor tyrosine kinases. Recently Zhou et al. (22) have carried out a systematic analysis of the contribution of distinct domains of MuSK to its ability to induce and associate with postsynaptic specializations. Their results indicate that deletion of the FRZ domain (consisting of a C6 box plus the Ig-IV region in the authors' terminology) specifically eliminates MusK/Rapsyn co-clustering.

The functional importance of the FRZ module may also explain the results of Forrester et al. (13). These authors have shown that the C. elegans Ror receptor tyrosine kinase cam-1 regulates cell motility and asymmetric cell division in the nematode; nonsense mutations lying within the FRZ domain of this receptor tyrosine kinase eliminate cam-1 function. The mutant phenotype is not due to loss of the activity of the downstream tyrosine kinase domain because mutations that lead only to loss of tyrosine kinase activity have only subtle effects on cell migrations (13). The observation of Afzal et al. (18) that missense mutations in the frizzled domain of Ror2 receptor tyrosine kinase can lead to Robinow syndrome indicates that this domain is essential for Ror2 function.

No ligands have been identified thus far for the Ror1 and Ror2 receptor tyrosine kinases. However, based on the presence of a FRZ module in the putative ligand-binding region, it has been suggested that WNT proteins might act as ligands for the FRZ modules of Rors (5, 6).

Despite the obvious biological importance of the FRZ module, nothing is known about its three-dimensional structure. In fact, there is still some controversy over whether the FRZ module corresponds to a single domain or is composed of two domains (5). This controversy stems primarily from the fact that in the middle of the FRZ module of Dror, there is a 55-amino acid insert between the fifth and sixth cysteines, separating the 10 conserved cysteines into two groups. Accordingly, the FRZ domain is sometimes subdivided into two regions, for example, the C6 box and the Ig-IV region in the case of MuSK (22).

To define the structure and function of this important module type, in the present work we have expressed the FRZ module of rat Ror1 in Pichia pastoris. Our structural studies on the recombinant protein indicate that the FRZ module corresponds to a single, compact, disulfide-bonded structural domain.

    EXPERIMENTAL PROCEDURES
TOP
ABSTRACT
INTRODUCTION
EXPERIMENTAL PROCEDURES
RESULTS AND DISCUSSION
REFERENCES

Cloning the FRZ Domain of Rat Ror1 Receptor Tyrosine Kinase-- The DNA segment coding for the frizzled domain of rat ROR1 receptor tyrosine kinase (residues Gly168-Ala304) was amplified with the 5'-CTGCCCGGGGCATATGGGNTTYTGYCARCCNTA-3' (sense) and 5'-CGCGGATCCTTANGCCATNGGHATNCCAA-3' (antisense) primers from a rat fetal brain cDNA library (CLONTECH). The amplified DNA was digested with SmaI and HindIII restriction endonucleases and ligated into M13mp19 Rf digested with the same enzymes. The sequence of the cloned DNA was determined by dideoxy sequencing on both strands.

Expression of the FRZ Module in P. pastoris-- The FRZ domain of rat ROR1 receptor tyrosine kinase was expressed in the methylotrophic yeast P. pastoris by utilizing the Easy Select P. pastoris expression kit (Invitrogen, Carlsbad, CA). The DNA fragment encoding the FRZ domain was excised from M13mp19/CR16 with SmaI-NcoI digestion and blunt-end-ligated into pPICZalpha A cut with EcoRI-XbaI. The sticky ends of the digested DNA fragment and the vector were filled with Klenow polymerase. The pPICZalpha A expression plasmid contains the zeocin resistance gene for easy selection of positive transformants, the inducible PAOX1 promoter of the alcohol oxidase 1 gene of P. pastoris, and the yeast alpha -mating factor secretion signal sequence. At the 3' end, the inserted DNA fragment was in-frame-ligated to the sequence encoding the c-myc epitope and a hexahistidine His tag. The plasmid contains the 3' termination signal of the AOX1 gene. Escherichia coli JM 109 cells were transformed with the ligation mixture and plated on low salt LB medium (1% tryptone, 0.5% yeast extract, and 0.5% NaCl) containing 25 µg/ml zeocin.

Zeocin-resistant colonies were screened for the presence of DNA encoding the FRZ domain by polymerase chain reaction using AOX1- and FRZ-specific primers and by restriction analysis. The plasmid pPICZalpha A/CR was linearized by BstXI digestion to promote the homologous recombination at the AOX1 locus of the yeast genome. The P. pastoris KM71 (HIS4-, AOX1-) strain was transformed by electroporation, and positive transformants were selected on zeocin-containing YPDS (1% yeast extract, 2% peptone, 2% dextrose, 1 M sorbitol, 100 µg/ml zeocin) plates as described in the Pichia Expression System users manual (Invitrogen). Zeocin-resistant colonies were screened for protein expression in small volume cultures according to a procedure described previously (23).

Thirty-two recombinant clones of P. pastoris were grown in 2-ml aliquots of BMGY (1% yeast extract, 2% peptone, 100 mM potassium phosphate, 1.34% yeast nitrogen base, 0.4 µg/ml biotin, and 1% glycerol) at 30 °C to an A600 = 15-20. Cell were collected by centrifugation and resuspended in 1-ml aliquots of BMMY (1% yeast extract, 2% peptone, 100 mM potassium phosphate, 1.34% yeast nitrogen base, 0.4 µg/ml biotin, and 1% methanol). The different recombinant clones were grown for 96 h at 30 °C with the addition of 1% methanol (final concentration) at 24-h intervals. Expression of recombinant protein was monitored by analyzing the culture fluids with SDS-PAGE.

The clone secreting the highest amount of recombinant protein was chosen for large scale protein expression. 400 ml of BMGY medium was inoculated with one colony of the appropriate yeast clone and grown at 30 °C to an A600 = 20-25. Cells were collected by centrifugation and resuspended in 200 ml of BMMY. The induction was continued for 168 h, and methanol addition was repeated at every 24 h.

The culture was centrifuged at 3,000 × g, and the supernatant was dialyzed against a 10-fold volume of distilled water. The pH of the dialysate was adjusted to 7.9, and then a 0.1 volume of 10× binding buffer (200 mM Tris and 50 mM imidazole, pH 7.9) was added. The solution was loaded on a 10-ml nickel-chelate column (Invitrogen), and then the column was washed with 10 volumes of washing buffer (20 mM Tris, 500 mM NaCl, and 30 mM imidazole, pH 7.9), and the bound protein was eluted with 20 mM Tris and 500 mM imidazole, pH 7.9.

The fractions containing recombinant FRZ module were pooled, lyophilized, desalted by gel filtration on Sephadex G-25, equilibrated with 0.1 M ammonium bicarbonate, pH 8.0, and lyophilized. The FRZ module was further purified by gel filtration on a Sephadex G-75 column, equilibrated with 0.1 M ammonium bicarbonate, pH 8.0, and lyophilized.

The recombinant protein was deglycosylated by digestion with endoglycosidase H (New England Biolabs, Beverly, MA). The recombinant protein (1 mg/ml) was dissolved in 50 mM sodium citrate, pH 5.5, and incubated with 500 New England Biolabs units of endoglycosidase H for 16 h at 37 °C. The digested protein was isolated by nickel-chelate column chromatography.

Circular Dichroism Spectroscopy-- CD spectra were measured over the range of 190-250 nm by using a JASCO J-720 spectropolarimeter thermostated with a Neslab RT-100 water bath. The measurements were carried out in 1-mm pathlength cells and protein solutions of ~0.1-0.3 mg/ml in 10 mM Tris-HCl buffer, pH 8.0. All spectra were measured at 25 °C with a 16 s time constant and a scan rate of 10 nm/min. The spectral slit width was 1.0 nm. All measurements represent the computer average of three scans. Secondary structure of recombinant proteins was estimated from their CD spectra with the J-720 program for Windows Secondary Structure Estimation Ver.1.10.00, JASCO.3.

Differential Scanning Calorimetry-- Calorimetric measurements were carried out on a VP-DSC MicroCalorimeter at a heating rate of 1 °C/min and a solution concentration of 0.2-0.5 mg/ml. Experiments were conducted at pH 8.0 in 20 mM Tris-HCl buffer. Buffer base lines were obtained under the same conditions and subtracted from sample tracings. The VP-DSC MicroCalorimeter was calibrated according to the instructions of the manufacturer. Differential scanning calorimetry data analysis was performed with the Microcal Origin Version 5.0 program.

Secondary Structure Prediction-- Secondary structure prediction of the FRZ module of rat Ror1 receptor tyrosine kinase, based on multiple alignments of FRZ modules, was carried out with previously described procedures (24-26) using the Profile Network Prediction Heidelberg (PHD) mail server. The PHD server predicts secondary structural elements by evaluating the relative probabilities that a given segment can be assigned to helix, strand, or loop. The estimated accuracy of this multiple alignment-based method for the correct prediction of secondary elements is about 72%.

Protein Analyses-- The composition of protein samples was analyzed by SDS-PAGE using 11-22% linear polyacrylamide gradient slab gels under both reducing and nonreducing conditions (27).

The concentration of the recombinant FRZ module of rat Ror1 receptor tyrosine kinase was determined using the extinction coefficient 6700 M-1 cm-1. The extinction coefficients were determined according to a method described previously (28).

Localization of Disulfide Bonds-- 170-µg samples of recombinant FRZ domain (in 70 µl of 1 mM HCl, pH 3) were digested with 1 µg of pepsin (Sigma) at room temperature for 2 h. 100 µl of 0.1 M ammonium acetate, pH 5.2, was added to the reaction mixture and digested with 8.5 µg of trypsin (Sigma) and 8.5 µg of chymotrypsin (Sigma) at 37 °C for 16 h. Samples were analyzed by reverse-phase HPLC on an Aquapore OD 300 (220 × 2.1-mm) C18 column (PE Applied Biosystems Ltd.) in 0.1% (by volume) trifluoroacetic acid with a linear gradient of acetonitrile. N-terminal sequencing was performed on an Applied Biosystems 471A protein sequencer with an on-line ABI 120A phenyltiohydantoin analyzer.

    RESULTS AND DISCUSSION
TOP
ABSTRACT
INTRODUCTION
EXPERIMENTAL PROCEDURES
RESULTS AND DISCUSSION
REFERENCES

Cloning and Expression of the FRZ Module of Rat Ror1 Receptor Tyrosine Kinase-- On the basis of the known sequences of human and mouse Ror1 receptor tyrosine kinases (GenBankTM accession numbers M97675 and AB010383), we have designed polymerase chain reaction primers for the amplification of the cDNA segment encoding the FRZ domain of rat Ror1 receptor tyrosine kinase. The amplified DNA fragment was cloned into M13 sequencing vector, and the nucleotide sequence was determined by dideoxy sequencing. Comparison of the nucleotide sequence of the FRZ module of rat Ror1 receptor tyrosine kinase with those of the human and mouse orthologues has revealed extensive sequence similarity (Fig. 2). The rat cDNA differs in 42 nucleotide positions from the human sequence and in 18 positions from the mouse sequence. The differences of nucleotide sequences are mainly in silent positions, resulting in only two and one amino acid substitutions relative to the human and mouse sequences, respectively (Fig. 2).


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Fig. 2.   Comparison of the nucleotide sequence of rat Ror1 (rRor1) receptor tyrosine kinase with those of the human (hRor1) and mouse (mRor1) orthologues. The top row shows the deduced amino acid sequence of the rat FRZ module. The bottom rows show the amino acid substitutions in the human and mouse sequences.

The cDNA encoding the FRZ domain of rat Ror1 receptor tyrosine kinase was subcloned into the pPICZalpha A P. pastoris expression vector. The cDNA was in-frame-ligated to the Saccharomyces cerevisiae prepro alpha -mating factor secretion signal sequence. This fused the FRZ domain after the KEX2 (Lys-Arg) and two STE13 (Glu-Ala-Glu-Ala) cleavage sites. Analysis of the culture media of the induced Pichia culture revealed that a protein of ~35-37 kDa is secreted efficiently, corresponding to an expression level of 20-25 mg/liter. The N-terminal amino acid sequence of the secreted protein was Glu-Ala-Glu-Leu-Gly-His-Met-Gly-Phe-Cys-Gln, showing that the secretion signal peptide was cut off at the first STE13 cleavage site, leaving the second Glu-Ala repeat at the N terminus of the secreted protein. Note that the segment of the recombinant protein originating from rat Ror1 receptor tyrosine kinase starts with Gly-Phe-Cys-Gln and terminates with Ile-Gly-Ile-Pro-Met (cf. Fig. 2).

The protein purified from the culture media by nickel-agarose chromatography appeared as a diffuse band on SDS-PAGE gels and had a molecular mass of ~35-37 kDa (Fig. 3), whereas the molecular mass calculated for the amino acid sequence of the recombinant protein was only 18.3 kDa. The FRZ module of rat Ror1 receptor tyrosine kinase possesses a potential N-glycosylation site (Asn-Arg-Thr) at Asn184, so we assumed that the higher molecular mass and the heterogeneity seen on SDS-PAGE gels may be due to N-glycosylation at this position. To test this explanation, we have subjected the recombinant protein to endoglycosidase treatment. Because P. pastoris synthesizes N-linked glycoproteins with high-mannose-type oligosaccharide side chains (29), we treated the secreted protein with endoglycosidase H, an enzyme that cleaves high-mannose-type glycans. Endoglycosidase H treatment has reduced the molecular mass of the recombinant protein to ~18 kDa (Fig. 3). The endoglycosidase H-treated protein gave a compact, sharp band on SDS-PAGE gels, indicating that the higher molecular mass and size heterogeneity of the recombinant protein were caused by the oligosaccharide side chain.


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Fig. 3.   SDS-PAGE of the recombinant FRZ module of rat Ror1 receptor tyrosine kinase expressed in P. pastoris. Lane 1, protein isolated from culture fluids by nickel-chelate column chromatography; lane 2, protein deglycosylated by endoglycosidase H treatment. St indicates the pattern of the Low Molecular Weight Calibration Kit (Amersham Pharmacia Biotech, Uppsala, Sweden; Mr values: 14,400, 20,100, 30,000, 43,000, 67,000, and 94,000). In lanes 1 and 2, ~20 µg of recombinant protein was loaded. The gels were stained with Coomassie Brilliant Blue G-250.

Structural Characterization of the Recombinant FRZ Module of Rat Ror1 Receptor Tyrosine Kinase-- Samples of glycosylated and deglycosylated rat Ror1 FRZ module were first analyzed by circular dichroism spectroscopy at far-ultraviolet wavelengths (190-250 nm). The two species gave very similar CD spectra, indicating that the N-glycan is not necessary for structural integrity and does not have a major effect on the secondary structural elements of the FRZ fold (Fig. 4). Analysis of the CD spectra of the recombinant FRZ module of rat Ror1 receptor tyrosine kinase (Fig. 4) predicts 40% beta -sheet and 23% alpha -helix. The presence of both beta -sheets and alpha -helices is consistent with the results of our secondary structure predictions for the FRZ module of rat Ror1 receptor tyrosine kinase (Fig. 5) and also seems to be generally valid for the large family of FRZ modules (6).


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Fig. 4.   Far-ultraviolet circular dichroism spectra of the recombinant FRZ module of rat Ror1 receptor tyrosine kinase. The solid line indicates the spectrum of the glycosylated FRZ module, the dashed line indicates the spectrum of the deglycosylated FRZ module. Spectra were obtained in 10 mM Tris-HCl, pH 8.0, at 25 °C using 0.1 mg/ml protein.


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Fig. 5.   Structure of the recombinant FRZ module of rat Ror1 receptor tyrosine kinase (rRor1). A, amino acid sequence and predicted secondary structure of the FRZ module of rRor1; the 10 conserved cysteines are numbered and highlighted in bold. PHD indicates the secondary structural elements (H, alpha -helix; E, beta -strand) predicted for FRZ of rRor1 with the PHD program. B, disulfide bond pattern of the FRZ module as derived from analysis of peptides shown in Table I.

To further clarify structural characteristics of FRZ modules, we have determined the disulfide bond pattern of the recombinant FRZ domain of Ror1 receptor tyrosine kinase. The peptides derived from the recombinant protein by digestion with pepsin, trypsin, and chymotrypsin were subjected to N-terminal amino acid sequence analysis. This analysis identified three disulphide-linked peptides (Fig. 6, peaks 20, 24, and 25) and allowed unambiguous assignment of disulphide linkages 1-5, 2-4, and 3-8 (Table I). Digestion with pepsin/trypsin/chymotrypsin did not cleave the peptide backbone between the sixth and seventh cysteines and between the ninth and tenth cysteines (fragment in peak 45; cf. Fig. 6 and Table I), therefore the fragment of peak 45 containing these cysteines was digested with V8 protease (Pierce; 2% by weight of peptide) in 0.1 M ammonium acetate, pH 5.2, at room temperature for 16 h. The reaction mixture was loaded onto the HPLC column, and the resulting peptides were sequenced. Sequence analysis has revealed a 7-9 and 6-10 disulfide bond pattern (Table I). Localization of disulfide bonds thus revealed a pattern with nested disulfide bonds (1-5 and 2-4 and 6-10 and 7-9) both in the N-terminal and C-terminal halves of the FRZ module (Fig. 5B). Nevertheless, the fact that these two halves are disulfide-bonded to each other through the third and eighth conserved cysteines argues against the contention that the FRZ module consists of two domains.


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Fig. 6.   HPLC separation of peptides derived from the recombinant FRZ module of rat Ror1 receptor tyrosine kinase by digestion with pepsin, trypsin, and chymotrypsin. Samples were analyzed by reverse-phase HPLC on an Aquapore OD 300 (220 × 2.1-mm) C18 column (PE Applied Biosystems Ltd.) in 0.1% (by volume) trifluoroacetic acid with a linear gradient of acetonitrile. Peptides identified by numbers in bold were used to define the disulfide pairings (cf. Table I). The solid line indicates the absorbance of the eluate at 220 nm.

                              
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Table I
Amino acid sequence of the disulfide-bonded peptides derived from the FRZ-module of Ror1 receptor tyrosine kinase by digestion with pepsin, trypsin, and chymotrypsin
The numbers refer to peptides isolated by HPLC as described in Fig. 6. Peptides 45A and 45B were derived from peptide 45 by digestion with V8 protease.

To further clarify whether the FRZ module consists of two domains or corresponds to a single domain, we have subjected the recombinant FRZ module to differential scanning calorimetry. The glycosylated protein had a Tm value of 103 °C (data not shown), and the deglycosylated domain had a Tm value of 84 °C (Fig. 7). Our observation that the N-glycan does not have a major effect on the secondary structure of the protein (Fig. 4) but increases its thermal stability is not unprecedented. Systematic comparison of glycosylated and deglycosylated forms of several proteins (30) have revealed that deglycosylation decreases thermal stability without a substantial effect on their conformation as indicated by the CD spectra in the ultraviolet range.


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Fig. 7.   Differential scanning calorimetry of the deglycosylated recombinant FRZ module of rat Ror1 receptor tyrosine kinase.

Thermal unfolding of the deglycosylated FRZ module was fully reversible, the enthalpy change of the unfolding was Delta Hcal = 50.5 ± 0.3 kcal/mol. The fact that the FRZ module of rat Ror1 receptor tyrosine kinase collapses with a single Tm value suggests that it corresponds to a single, compact fold, a finding that is not consistent with the suggestion that the FRZ domain could be subdivided into two distinct domains (5, 22).

    FOOTNOTES

* This work was supported by Grants OTKA T022949 and OTKA T014642 of the Hungarian Research Fund, Budapest, Hungary.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

To whom correspondence should be addressed. Tel.: 361-4665-633; Fax: 361-4665-465; E-mail: patthy@enzim.hu.

Published, JBC Papers in Press, February 21, 2001, DOI 10.1074/jbc.M100100200

    ABBREVIATIONS

The abbreviations used are: FRZ, frizzled; MuSK, muscle-specific tyrosine kinase; SDS-PAGE, SDS-polyacrylamide gel electrophoresis; HPLC, high pressure liquid chromatography.

    REFERENCES
TOP
ABSTRACT
INTRODUCTION
EXPERIMENTAL PROCEDURES
RESULTS AND DISCUSSION
REFERENCES

1. Cadigan, K. M., and Nusse, R. (1997) Genes Dev. 11, 3286-3305[Free Full Text]
2. Bhanot, P., Brink, M., Samos, C. H., Hsieh, J. C., Wang, Y., Macke, J. P., Andrew, D., Nathans, J., and Nusse, R. (1996) Nature 382, 225-230[CrossRef][Medline] [Order article via Infotrieve]
3. Masiakowski, P., and Yancopoulos, G. D. (1998) Curr. Biol. 8, R407[Medline] [Order article via Infotrieve]
4. Saldanha, J., Singh, J., and Mahadevan, D. (1998) Protein Sci. 7, 1632-1635[CrossRef]
5. Xu, Y. K., and Nusse, R. (1998) Curr. Biol. 8, R405-R406[Medline] [Order article via Infotrieve]
6. Rehn, M., Pihlajaniemi, T., Hoffmann, K., and Bucher, P. (1998) Trends Biochem. Sci. 23, 415-417[CrossRef][Medline] [Order article via Infotrieve]
7. Tomita, Y., Kim, D.-H., Magoori, K., Fujino, T., and Yamamoto, T. T. (1998) J. Biochem. (Tokyo) 124, 784-789[Abstract]
8. DeChiara, T. M., Bowen, D. C., Valenzuela, D. M., Simmons, M. V., Poueymirou, W. T., Thomas, S., Kinetz, E., Compton, D. L., Rojas, E., Park, J. S., Smith, C., DiStefano, P. S., Glass, D. J., Burden, S. J., and Yancopoulos, G. D. (1996) Cell 85, 501-512[Medline] [Order article via Infotrieve]
9. Glass, D. J., Bowen, D. C., Stitt, T. N., Radziejewski, C., Bruno, J., Ryan, T. E., Gies, D. R., Shah, S., Mattsson, K., Burden, S. J., DiStefano, P. S., Valenzuela, D. M., DeChiara, T. M., and Yancopoulos, G. D. (1996) Cell 85, 513-523[Medline] [Order article via Infotrieve]
10. Burden, S. J. (1998) Genes Dev. 12, 133-148[Free Full Text]
11. Wilson, C., Goberdhan, D. C., and Steller, H. (1993) Proc. Natl. Acad. Sci. U. S. A. 90, 7109-7113[Abstract]
12. Oishi, I., Sugiyama, S., Liu, Z. J., Yamamura, H., Nishida, Y., and Minami, Y. (1997) J. Biol. Chem. 272, 11916-11923[Abstract/Free Full Text]
13. Forrester, W. C., Deil, M., Perens, E., and Garriga, G. (1999) Nature 400, 881-885[CrossRef][Medline] [Order article via Infotrieve]
14. Oishi, I., Takeuchi, T., Hashimoto, R., Nagabukuro, A., Ueda, T., Liu, Z.-J., Hatta, T., Akira, S., Matsuda, Y., Yamamura, H., Otani, H., and Minami, Y. (1999) Genes Cells 4, 41-56[Abstract/Free Full Text]
15. Takeuchi, S., Takeda, K., Oishi, I., Nomi, M., Ikeya, M., Itoh, K., Tamura, S., Ueda, T., Hatta, T., Otani, H., Terashima, T., Takada, S., Yamamura, H., Akira, S., and Minami, Y. (2000) Genes Cells 5, 71-78[Abstract/Free Full Text]
16. DeChiara, T. M., Kimble, R. B., Poueymirou, W. T., Rojas, J., Masiakowski, P., Valenzuela, D. M., and Yancopoulos, G. D. (2000) Nat. Genet. 24, 271-274[CrossRef][Medline] [Order article via Infotrieve]
17. Oldridge, M., Fortuna, A.-M., Maringa, M., Propping, P., Mansour, S., Pollitt, C., DeChiara, T. M., Kimble, R. B., Valenzuela, D. M., Yancopoulos, G. D., and Wilkie, A. O. M. (2000) Nat. Genet. 24, 275-278[CrossRef][Medline] [Order article via Infotrieve]
18. Afzal, A. R., Rajab, A., Fenske, C. D., Oldridge, M., Elanko, N., Ternes-Pereira, E., Tuysuz, B., Murday, V. A., Patton, M. A., Wilkie, A. O., and Jeffery, S. (2000) Nat. Genet. 25, 419-422[CrossRef][Medline] [Order article via Infotrieve]
19. van Bokhoven, H., Celli, J., Kayserili, H., van Beusekom, E., Balci, S., Brussel, W., Skovby, F., Kerr, B., Percin, E. F., Akarsu, N., and Brunner, H. G. (2000) Nat. Genet. 25, 423-426[CrossRef][Medline] [Order article via Infotrieve]
20. Masiakowski, P., and Carroll, R. D. (1992) J. Biol. Chem. 267, 26181-26190[Abstract/Free Full Text]
21. Valenzuela, D. M., Stitt, T. N., DiStefano, P. S., Rojas, E., Mattsson, K., Compton, D. L., Nunez, L., Park, J. S., Stark, J. L., Gies, D. R., Thomas, S., Le Beau, M. M., Fernald, A. A., Copeland, N. G., Jenkins, N. A., Burden, S. J., Glass, D. J., and Yancopoulos, G. D. (1995) Neuron 1995, 573-584
22. Zhou, H., Glass, D. J., Yancopoulos, G. D., and Sanes, J. R. (1999) J. Cell Biol. 146, 1133-1146[Abstract/Free Full Text]
23. Steinlein, L. M., Ligman, C. M., Kessler, S., and Ikeda, R. A. (1998) Biochemistry 37, 13696-13703[CrossRef][Medline] [Order article via Infotrieve]
24. Rost, B., and Sander, C. (1994) Proteins 19, 55-77[Medline] [Order article via Infotrieve]
25. Rost, B. (1995) in The Third International Conference on Intelligent Systems for Molecular Biology (Rawlings, C. , Clark, D. , Altman, R. , Hunter, L. , Lengauer, T. , and Wodak, S., eds) , pp. 314-321, AAAI Press, Menlo Park, CA
26. Rost, B. (1996) Methods Enzymol. 266, 525-539[CrossRef][Medline] [Order article via Infotrieve]
27. Laemmli, U. K. (1970) Nature 227, 680-685[Medline] [Order article via Infotrieve]
28. Mach, H., Middaugh, C. R., and Lewis, R. V. (1992) Anal. Biochem. 200, 74-80[Medline] [Order article via Infotrieve]
29. Grinna, L. S., and Tschopp, J. F. (1989) Yeast 5, 107-115[Medline] [Order article via Infotrieve]
30. Wang, C., Eufemi, M., Turano, C., and Giartosio, A. (1996) Biochemistry 35, 7299-7307[CrossRef][Medline] [Order article via Infotrieve]


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