From the Howard Hughes Medical Institute, Departments of Internal Medicine and Physiology and Biophysics, University of Iowa College of Medicine, Iowa City, Iowa 52242
Since the sequence of the
CFTR1 Cl The R domain was originally defined as those residues encoded by
exon 13 (aa 590-830) (Fig. 1) (1).
Although the precise boundaries of the R domain remain uncertain,
recent studies suggest that the N-terminal portion of exon 13 is
actually part of NBD1, whereas the C-terminal portion constitutes the
structural and functional "R domain." Supporting this conclusion,
the N-terminal portion of exon 13 has sequence similarity with NBDs of
other ABC transporters (4, 5). More recently, crystal structures were
solved for the NBDs of the ABC transporters HisP, MalK, and Rad50
(6-8). In CFTR, residues analogous to those NBDs would extend to
approximately aa 642. Experimental evidence for the boundaries came
with the demonstration that deletion of aa 708-835, but not deletions
extending further in the N-terminal direction, produced a channel that
was processed correctly, opened in the presence of ATP, and had
conductive properties like those of wild-type CFTR (4, 9). In addition,
severing CFTR after residues 633 or 835 and coexpressing the two halves
in Xenopus oocytes produced functional channels, whereas
severing the channel between exons 12 and 13 abolished function (10,
11). All these data suggest that the N-terminal R domain boundary
begins between residues 634 and 708 and that the C-terminal boundary
ends in the region of residue 835.
INTRODUCTION
channel was discovered, the
function of its R domain has been puzzling. CFTR is a member of the
ATP-binding cassette (ABC) transporter
family, and it contains the features characteristic of this family: two
nucleotide binding domains (NBDs) and two membrane-spanning domains
(MSDs) (1). Yet in addition, CFTR also contains the R domain, a unique
sequence not found in other ABC transporters or any other proteins. The R domain serves as the major physiologic regulator of the CFTR Cl
channel (2, 3). Upon elevation of cAMP levels,
cAMP-dependent protein kinase (PKA) phosphorylates the R
domain allowing ATP to open and close the channel. Yet how
phosphorylation activates the channel is not well understood. Some
models propose that the R domain prevents the channel from opening and
that phosphorylation relieves this inhibition. Other models suggest
that phosphorylation of the R domain stimulates activity. Here we
briefly review current knowledge that may help explain the function of
this interesting domain.
Sequence and Boundaries of the R Domain
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Fig. 1.
Sequence of exon 13 of CFTR. The
underline indicates a region comparable with the crystal
structure of NBDs of other ABC transporters. Red indicates
sequences that are identical or conserved across species. The
gray shading indicates PKA consensus motifs that
are phosphorylated in vitro, and the yellow
shading indicates those sites also phosphorylated in
vivo. Reported variants that change aa sequence are displayed
below the appropriate residue.
The most striking feature of the R domain is the presence of multiple
consensus PKA phosphorylation sites that are highly conserved across
species (Fig. 1). There is little other sequence similarity in the R
domain, unlike the substantial sequence conservation throughout the
rest of CFTR. We are not aware of any other conserved protein motifs in
the R domain, although there is a relatively high percentage (28%) of
charged residues. Sixteen of the 24 basic residues are in PKA consensus
sites. Several of the acidic residues are clustered within 817-838
(12).
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Phosphorylation of the R Domain |
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PKA is the primary kinase that phosphorylates CFTR, although protein kinase C, cGMP-dependent protein kinase, and tyrosine phosphorylation can also stimulate channel activity (2, 3). In vitro, PKA phosphorylates Ser-660, Ser-700, Ser-712, Ser-737, Ser-753, Ser-768, Ser-795, and Ser-813 (13, 14). PKA also phosphorylates these residues plus Ser-686 in isolated R domain proteins or peptides (14-16). In contrast, when CFTR is phosphorylated in cells by addition of cAMP agonists, detectable phosphorylation is limited to Ser-660, Ser-700, Ser-737, Ser-795, and Ser-813 (13, 14, 17).
The functional consequences of phosphorylation have been evaluated by
studying CFTR mutated at one or many of the phosphorylatable serines
(13, 15, 18-23). Serine mutations reduced but did not abolish
phosphorylation-stimulated activity, and no single serine was required
for stimulation. Even when all the consensus phosphoserines were
mutated, a small amount of PKA-mediated Cl current
remained, suggesting a contribution from sites that are not normally
phosphorylated in vivo such as Ser-753 (15, 19). Nonetheless, the majority of PKA-dependent stimulation
appears to result from phosphorylation of Ser-660, Ser-700, Ser-737,
Ser-795, and Ser-813.
Although no one serine is essential, individual serines seem to stimulate channel activity to different degrees. For example, mutation of either Ser-660 or Ser-813 reduced the open state probability (Po) of CFTR studied under several conditions (20, 21, 23). Thus, these two residues play key stimulatory roles. Phosphorylation of Ser-795 also stimulated, although to a lesser extent (21, 23). Interestingly, the consequences of mutating Ser-737 differed depending upon how it was studied. In excised, cell-free patches, the S737A mutant reduced Po (20), but in Xenopus oocytes and epithelia, the S737A mutant increased cAMP-stimulated current (21, 23). We speculate that these differences may be because of loss of kinases, phosphatases, or associated molecules after membrane excision.
Various phosphoserines also show functional interactions. For example,
mutating either Ser-660 or Ser-813 alone reduced
phosphorylation-stimulated activity. However, when either Ser-660 or
Ser-813 was present in a variant in which the other phosphorylation
sites were mutated, current did not increase; both Ser-660 and Ser-813
were essential for current to reach wild-type levels (23). Likewise,
Ser-737 was unable to stimulate or inhibit unless other serines were
also present (21, 23). These data suggest either concomitant or sequential phosphorylation events may be required.
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Does the Unphosphorylated R Domain Inhibit Channel Activity? |
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Additional clues to R domain function came from studies of R
domain deletions. Deleting aa 708-835 (R) or 768-830 (Fig.
2) generated channels that were open in
the presence of ATP but did not require phosphorylation,
i.e. they were constitutively active (4, 24, 25). These data
suggested that the unphosphorylated R domain inhibits activity and that
phosphorylation or deletion eliminates the inhibition. This led to the
proposal that the R domain might be an inhibitory particle, much like
the N terminus of the Shaker K+ channel (26). However, that
hypothesis is difficult to reconcile with data showing that the mere
presence of an R domain is insufficient to inhibit constitutive
activity. For example, coexpressing two halves of CFTR (aa 1-835
and aa 837-1480) that retain the R domain generated a constitutively
active channel (Fig. 2) (11, 27). Likewise, translocating aa
709-835 to the C terminus of CFTR-
R produced constitutively active
channels (28). Moreover, adding isolated unphosphorylated R domain
proteins encompassing aa 645-834, 590-858, or 708-831 did not reduce
constitutive activity of CFTR-
R (20, 24, 29).
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To identify R domain sequences that might prevent constitutive activity, other deletions were studied. A smaller R domain deletion (aa 760-835) also induced constitutive activity, whereas deletions of residues 708-759, 784-835, and 780-830 did not (Fig. 2) (25, 28). This focused attention on residues 760-783; deletion of these residues generated a constitutively active channel (28). There are no obvious sequence motifs between aa 760 and 783, although the sequence 765RRQSVL(N/D)LMT774 is conserved across species. Ser-768 is located in this region, but it is not phosphorylated in vivo (13, 14), and its mutation did not induce constitutive activity (21, 28). Interestingly, adding residues 760-783 as isolated peptides or translocating them to the C terminus failed to prevent constitutive activity (Fig. 2).
Thus, the R domain probably has an inhibitory function that
requires a small portion in the middle of the domain. However, those residues alone are not sufficient to prevent
constitutive activity, and to have an effect it appears that
they must be retained in their normal location between NBD1
and MSD2.
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Does the Phosphorylated R Domain Stimulate Channel Activity? |
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Direct evidence that the phosphorylated R domain is stimulatory
came from studies that added isolated R domain proteins to CFTR-R
channels. Phosphorylated, but not unphosphorylated, proteins consisting
of residues 645-834, 590-858, and 708-831 each stimulated Cl
current (Fig. 2) (20, 24, 29). In addition,
translocating aa 709-835, 709-759, or 760-835 to the C terminus
restored PKA-stimulated activity to CFTR-
R (28). One study
suggesting that the R domain is not stimulatory found that channels
generated by coexpressing aa 3-633 and 837-1480 opened as often as
wild type (Fig. 2) (11). However, the Po of those
severed channels was only half that of wild-type channels. Another
study found that deleting the negatively charged region at aa 817-838
generated a constitutively active channel whose activity was not
increased by PKA (Fig. 2) (12). This finding suggested that this
relatively conserved region was required for stimulation.
These data clearly indicate that the R domain can stimulate activity,
although the mechanism is unknown. Interestingly, stimulation can come
from multiple R domain regions, more than one phosphoserine can
stimulate, and no one specific phosphoserine or unique sequence is
required. The data also suggest that stimulatory regions differ from
those preventing constitutive activity.
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R Domain Phosphorylation Enhances ATP Interaction with the NBDs |
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Phosphorylation raises Po by increasing the
rate at which the channel opens (20, 22, 24). Phosphorylation also increases the apparent affinity of the NBDs for ATP; this effect differs for different phosphoserines (20, 22). In general the more
phosphorylation, the greater the activity. This is likely to be of
physiologic importance, as graded phosphorylation could generate graded
apical membrane Cl channel activity allowing precise
control of transepithelial Cl
transport.
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The R Domain Is Predominantly Unstructured in Solution |
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To better understand the functional and structural features of this unique domain, we expressed and purified an R domain protein comprising aa 708-831 (named R8) (29). Analytical ultracentrifugation showed that soluble R8 was a monomer, and limited proteolysis indicated that most of R8 was accessible to proteases. Phosphorylation did not change these properties, suggesting that it did not induce global conformational changes. Importantly, phosphorylated R8 stimulated channel activity, suggesting that if the R domain has a specific structure, it is retained in this protein.
Circular dichroism (CD) suggested that R8 had little well ordered
secondary structure; helical content was about 5% with the remaining
protein being random coil (29). The results were the same irrespective
of whether spectra were obtained in high pH, low salt, buffers used for
patch-clamp studies, trimethylamine oxide (which promotes protein
folding), or R8 incorporated in phospholipid micelles. Phosphorylated
and nonphosphorylated R8 had similar CD spectra, suggesting that
phosphorylation did not induce large structural changes. CD spectra of
larger R domain proteins including all or parts of NBD1 revealed
significant secondary structure; aa 595-831 had 10% -helix and
30%
-sheet (30), whereas aa 404-830 had 19%
-helix and 43%
-sheet (16). The secondary structure in those proteins may arise
from the NBD1 portion and the random coil from the R domain.
Although other ABC transporters do not contain a region homologous to the R domain, P-glycoprotein contains a central region connecting NBD1 and MSD2 that includes two PKA motifs. Deleting this linker region (aa 653-686) disrupted drug transport and ATP hydrolysis (31). Replacing the linker with an unrelated sequence predicted to form a flexible structure restored both drug transport and ATP hydrolysis. Interestingly, when linker residues 644-689 from P-glycoprotein replaced aa 780-830 in CFTR, stimulated channel activity was restored to wild-type levels (25). These observations suggest that a defined amino acid sequence is not critical, but PKA consensus motifs, a certain degree of flexibility, and possibly an optimal length are key in determining channel activity.
Several other observations support the conclusion that the functional R
domain is predominantly random coil. First, the entire R domain was
neither required to stimulate activity nor to prevent constitutive
activity; portions were sufficient (Fig. 2). If the R domain had a well
ordered tertiary structure, such alterations would likely be
disruptive. Second, the R domain sequence is not well conserved across
species (Fig. 1). Most highly structured domains show substantial
sequence conservation; examples are the NBDs. Moreover, many of the
conserved residues in such proteins have hydrophobic side chains buried
within the protein core where they help maintain structure (32). In
contrast, the conserved R domain sequences are consensus PKA
phosphorylation motifs that are expected to be solvent-exposed where
they serve functional rather than structural roles. Third, of the more
than 972 mutations and variations reported in the CFTR
gene,2 only 9 missense
variations lie between aa 708 and 831; two are at conserved PKA motifs
(Fig. 1). Note, however, that not all of these reported sequence
variations are actually known to cause cystic fibrosis because
clinical information is limited. Of these 9, for the few variants that
have been studied, their biosynthesis does not differ from wild-type
(34), consistent with the idea that an amino acid change in random coil
would be unlikely to disrupt structure. Moreover, these variants show
relatively small functional differences (34).
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How Does an R Domain Composed Primarily of Random Coil Regulate Activity? |
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If the R domain is predominantly random coil and if
phosphorylation does not increase overall structure, how does the R
domain regulate the channel? There are several possibilities.
(a) Phosphorylation might induce a conformational change but
only in small discrete regions. (b) Introduction of negative
charge by phosphorylation may be sufficient to initiate activity;
consistent with this, replacement of serines with aspartates stimulates
activity (18). (c) Phosphorylation may not directly change
conformation but may be required before the R domain can interact with
other sites within CFTR. (d) The R domain may adopt a more
ordered structure only upon contact with the rest of CFTR. The last two
possibilities are reminiscent of the interaction of the
kinase-inducible domain (KID) of the cAMP-responsive element-binding
protein (CREB) with CREB-binding protein (CBP). Several structural
parameters indicate that KID is unstructured, and serine
phosphorylation does not increase structure (35-39). However, just as
phosphorylation allows the R domain to activate the Cl
channel, phosphorylation allows KID to bind and activate CBP. This
binding induces a conformational change in KID, which is limited to the
phosphoserine and a few neighboring amino acids.
How does a phosphorylated random coil R domain stimulate activity? Fig.
3 shows some speculative models (29). The
phosphorylated R domain might interact with a single (B) or
multiple sites (C and D) on the rest of CFTR.
Interactions may be specific (C) or nonspecific
(D). The number of phosphoserines and interaction sites is
arbitrary and for illustrative purposes only. In this model, we
emphasize the advantages of an unstructured but phosphorylated R domain
for stimulation. However, the model does not show how an
unphosphorylated R domain prevents constitutive activity. Our current
level of understanding makes it difficult to include both stimulatory
and inhibitory aspects in the same model.
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Model A shows the unphosphorylated R domain as a random coil. Without phosphorylation, it does not stimulate activity. Model B shows a phosphorylated R domain. Because the R domain is unstructured, any of several different phosphoserines could interact with the single site to stimulate activity. Model B could explain the ability of multiple different phosphoserines to stimulate, possibly with quantitatively different effects on activity. Model C shows multiple phosphoserines interacting with unique sites in CFTR. This model could account for increasing activity with increasing phosphorylation; if there were 3, 4, or 5 phosphoserines, there would be 3, 4, or 5 matching interaction sites. This model could also account for quantitatively different effects generated by phosphorylation of different serines.
Model D shows multiple phosphoserines interacting with
multiple binding sites. Here we show only two, suggesting the
possibility of at least one interaction site at each NBD. However, more
interaction sites may exist, as evidenced by the observation that
regions within the R domain and the N terminus interact (40). Model D could account for the apparent promiscuous relationship
between phosphorylation sites and stimulation of activity as depicted by the arrows. In such a model, a relatively unstructured R
domain would allow multiple different phosphoserines to stimulate, no one phosphoserine would be required, different phosphoserines could
have quantitatively different effects, and the more serines phosphorylated, the greater the activity.
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Advantages of Intrinsically Unstructured Domains |
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There is increasing recognition that many protein domains and full-length proteins are intrinsically unstructured (41, 42). Examples include the cell cycle kinase inhibitor p21waf1/Cip1/Sdi1 (43), the FlgM flagellar protein of Salmonella typhimurium (44), and the fibronectin receptor-binding protein (45). Interestingly, a regulatory sequence in another channel, the fast inactivation domain of the Shaker B K+ channel, also acts in a structure-independent manner (33). The advantages of unfolded proteins for signaling or regulation are also becoming more apparent (41, 42). In CFTR, an R domain composed predominantly of random coil would retain the flexibility that permits facile interaction with multiple regions within the rest of CFTR and allow prompt, discrete, and variable reactions to phosphorylation of different serines.
Despite extensive study on the R domain, a number of critical questions
remain. Why is spacing of PKA motifs conserved within random coil? Why
are certain regions within the R domain necessary but not sufficient
for inhibition, and why can't those residues be translocated within
the molecule and retain function? Finally, what is the mechanism by
which the R domain stimulates and inhibits the channel?
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ACKNOWLEDGEMENTS |
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We thank Theresa Mayhew for excellent assistance and our colleagues for helpful discussion.
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FOOTNOTES |
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* This minireview will be reprinted in the 2001 Minireview Compendium, which will be available in December, 2001. This work was supported by National Heart Lung and Blood Institute Grant HL42385 and by the Howard Hughes Medical Institute.
Investigator of the Howard Hughes Medical Institute. To whom
correspondence should be addressed: Howard Hughes Medical Inst., University of Iowa College of Medicine, 500 EMRB, Iowa City, IA 52242. Tel.: 319-335-7619; Fax: 319-335-7623; E-mail: mjwelsh@ blue.weeg.uiowa.edu.
Published, JBC Papers in Press, January 23, 2001, DOI 10.1074/jbc.R100001200
2 CF Genetic Analysis Consortium, unpublished data.
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ABBREVIATIONS |
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The abbreviations used are: CFTR, cystic fibrosis transmembrane conductance regulator; ABC, ATP-binding cassette; NBD, nucleotide binding domain; MSD, membrane-spanning domain; PKA, protein kinase A; aa, amino acid(s); KID, kinase-inducible domain; CREB, cAMP-responsive element-binding protein; CBP, CREB-binding protein.
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REFERENCES |
---|
1. | Riordan, J. R., Rommens, J. M., Kerem, B. S., Alon, N., Rozmahel, R., Grzelczak, Z., Zielenski, J., Lok, S., Plavsic, N., Chou, J. L., Drumm, M. L., Iannuzzi, M. C., Collins, F. S., and Tsui, L. C. (1989) Science 245, 1066-1073[Medline] [Order article via Infotrieve] |
2. | Sheppard, D. N., and Welsh, M. J. (1999) Physiol. Rev. 79, S23-S45[Medline] [Order article via Infotrieve] |
3. | Gadsby, D. C., and Nairn, A. C. (1999) Physiol. Rev. 79, S77-S107[Medline] [Order article via Infotrieve] |
4. | Rich, D. P., Gregory, R. J., Anderson, M. P., Manavalan, P., Smith, A. E., and Welsh, M. J. (1991) Science 253, 205-207[Medline] [Order article via Infotrieve] |
5. | Dulhanty, A. M., and Riordan, J. R. (1994) FEBS Lett. 343, 109-114[CrossRef][Medline] [Order article via Infotrieve] |
6. | Hung, L. W., Wang, I. X., Nikaido, K., Liu, P. Q., Ames, G. F. L., and Kim, S. H. (1998) Nature 396, 703-707[CrossRef][Medline] [Order article via Infotrieve] |
7. | Hopfner, K. P., Karcher, A., Shin, D. S., Craig, L., Arthur, L. M., Carney, J. P., and Tainer, J. A. (2000) Cell 101, 789-800[Medline] [Order article via Infotrieve] |
8. |
Diederichs, K.,
Diez, J.,
Greller, G.,
Muller, C.,
Breed, J.,
Schnell, C.,
Vonrhein, C.,
Boos, W.,
and Welte, W.
(2000)
EMBO J.
19,
5951-5961 |
9. | Rich, D. P., Gregory, R. J., Cheng, S. H., Smith, A. E., and Welsh, M. J. (1993) Receptors Channels 1, 221-232[Medline] [Order article via Infotrieve] |
10. |
Chan, K. W.,
Csanady, L.,
Seto-Young, D.,
Nairn, A. C.,
and Gadsby, D. C.
(2000)
J. Gen. Physiol.
116,
163-180 |
11. |
Csanady, L.,
Chan, K. W.,
Seto-Young, D.,
Kopsco, D. C.,
Nairn, A. C.,
and Gadsby, D. C.
(2000)
J. Gen. Physiol.
116,
477-500 |
12. |
Xie, J.,
Zhao, J.,
Davis, P. B.,
and Ma, J.
(2000)
Biophys. J.
78,
1293-1305 |
13. | Cheng, S. H., Rich, D. P., Marshall, J., Gregory, R. J., Welsh, M. J., and Smith, A. E. (1991) Cell 66, 1027-1036[Medline] [Order article via Infotrieve] |
14. |
Picciotto, M. R.,
Cohn, J. A.,
Bertuzzi, G.,
Greengard, P.,
and Nairn, A. C.
(1992)
J. Biol. Chem.
267,
12742-12752 |
15. |
Seibert, F. S.,
Tabcharani, J. A.,
Chang, X. B.,
Dulhanty, A. M.,
Mathews, C.,
Hanrahan, J. W.,
and Riordan, J. R.
(1995)
J. Biol. Chem.
270,
2158-2162 |
16. | Neville, D. C. A., Rozanas, C. R., Tulk, B. M., Townsend, R. R., and Verkman, A. S. (1998) Biochemistry 37, 2401-2409[CrossRef][Medline] [Order article via Infotrieve] |
17. | Cohn, J. A., Nairn, A. C., Marino, C. R., Melhus, O., and Kole, J. (1992) Proc. Natl. Acad. Sci. U. S. A. 89, 2340-2344[Abstract] |
18. |
Rich, D. P.,
Berger, H. A.,
Cheng, S. H.,
Travis, S. M.,
Saxena, M.,
Smith, A. E.,
and Welsh, M. J.
(1993)
J. Biol. Chem.
268,
20259-20267 |
19. |
Chang, X. B.,
Tabcharani, J. A.,
Hou, Y. X.,
Jensen, T. J.,
Kartner, N.,
Alon, N.,
Hanrahan, J. W.,
and Riordan, J. R.
(1993)
J. Biol. Chem.
268,
11304-11311 |
20. | Winter, M. C., and Welsh, M. J. (1997) Nature 389, 294-296[CrossRef][Medline] [Order article via Infotrieve] |
21. |
Wilkinson, D. J.,
Strong, T. V.,
Mansoura, M. K.,
Wood, D. L.,
Smith, S. S.,
Collins, F. S.,
and Dawson, D. C.
(1997)
Am. J. Physiol.
273,
L127-L133 |
22. |
Mathews, C. J.,
Tabcharani, J. A.,
Chang, X. B.,
Jensen, T. J.,
Riordan, J. R.,
and Hanrahan, J. W.
(1998)
J. Physiol.
508,
365-377 |
23. | Baldursson, O., Berger, H. A., and Welsh, M. J. (2000) Am. J. Physiol. 279, L835-L841 |
24. |
Ma, J.,
Zhao, J.,
Drumm, M. L.,
Xie, J.,
and Davis, P. B.
(1997)
J. Biol. Chem.
272,
28133-28141 |
25. | Vankeerberghen, A., Lin, W., Jaspers, M., Cuppens, H., Nilius, B., and Cassiman, J. J. (1999) Biochemistry 38, 14988-14998[CrossRef][Medline] [Order article via Infotrieve] |
26. | Hoshi, T., Zagotta, W. N., and Aldrich, R. W. (1990) Science 250, 533-538[Medline] [Order article via Infotrieve] |
27. | King, S. A., and Sorscher, E. J. (2000) Biochemistry 39, 9868-9875[CrossRef][Medline] [Order article via Infotrieve] |
28. |
Baldursson, O.,
Ostedgaard, L. S.,
Rokhlina, T.,
Cotten, J. F.,
and Welsh, M. J.
(2001)
J. Biol. Chem.
276,
1904-1910 |
29. |
Ostedgaard, L. S.,
Baldursson, O.,
Vermeer, D. W.,
Welsh, M. J.,
and Robertson, A. D.
(2000)
Proc. Natl. Acad. Sci. U. S. A.
97,
5657-5662 |
30. | Dulhanty, A. M., and Riordan, J. R. (1994) Biochemistry 33, 4072-4079[Medline] [Order article via Infotrieve] |
31. | Hrycyna, C. A., Airan, L. E., Germann, U. A., Ambudkar, S. V., Pastan, I., and Gottesman, M. M. (1998) Biochemistry 37, 13660-13673[CrossRef][Medline] [Order article via Infotrieve] |
32. | Bowie, J. U., Reidhaar-Olson, J. F., Lim, W. A., and Sauer, R. T. (1990) Science 247, 1306-1310[Medline] [Order article via Infotrieve] |
33. | Murrell-Lagnado, R. D., and Aldrich, R. W. (1993) J. Gen. Physiol. 102, 949-975[Abstract] |
34. |
Vankeerberghen, A.,
Wei, L.,
Jaspers, M.,
Cassiman, J. J.,
Nilius, B.,
and Cuppens, H.
(1998)
Hum. Mol. Genet.
7,
1761-1769 |
35. |
Richards, J. P.,
Bächinger, H. P.,
Goodman, R. H.,
and Brennan, R. G.
(1996)
J. Biol. Chem.
271,
13716-13723 |
36. | Radhakrishnan, I., Perez-Alvarado, G. C., Parker, D., Dyson, H. J., Montminy, M. R., and Wright, P. E. (1997) Cell 91, 741-752[Medline] [Order article via Infotrieve] |
37. | Radhakrishnan, I., Perez-Alvarado, G. C., Dyson, H. J., and Wright, P. E. (1998) FEBS Lett. 430, 317-322[CrossRef][Medline] [Order article via Infotrieve] |
38. | Parker, D., Ferreri, K., Nakajima, T., LaMorte, V. J., Evans, R., Koerber, S. C., Hoeger, C., and Montminy, M. R. (1996) Mol. Cell. Biol. 16, 694-703[Abstract] |
39. |
Parker, D.,
Rivera, M.,
Zor, T.,
Henrion-Caude, A.,
Radhakrishnan, I.,
Kumar, A.,
Shapiro, L. H.,
Wright, P. E.,
Montminy, M.,
and Brindle, P. K.
(1999)
Mol. Cell. Biol.
19,
5601-5607 |
40. |
Naren, A. P.,
Cormet-Boyaka, E.,
Fu, J.,
Villain, M.,
Blalock, J. E.,
Quick, M. W.,
and Kirk, K. L.
(1999)
Science
286,
544-548 |
41. | Plaxco, K. W., and Groß, M. (1997) Nature 386, 657-659[CrossRef][Medline] [Order article via Infotrieve] |
42. | Wright, P. E., and Dyson, H. J. (1999) J. Mol. Biol. 293, 321-331[CrossRef][Medline] [Order article via Infotrieve] |
43. |
Kriwacki, R. W.,
Hengst, L.,
Tennant, L.,
Reed, S. I.,
and Wright, P. E.
(1996)
Proc. Natl. Acad. Sci. U. S. A.
93,
11504-11509 |
44. | Daughdrill, G. W., Chadsey, M. S., Karlinsey, J. E., Hughes, K. T., and Dahlquist, F. W. (1997) Nat. Struct. Biol. 4, 285-291[Medline] [Order article via Infotrieve] |
45. | Penkett, C. J., Redfield, C., Dodd, I., Hubbard, J., McBay, D. L., Mossakowska, D. E., Smith, R. A. G., Dobson, C. M., and Smith, L. J. (1997) J. Mol. Biol. 274, 152-159[CrossRef][Medline] [Order article via Infotrieve] |