1 Structural Biology Program, Skirball Institute of Biomolecular Medicine, Departments of 1Biochemistry, New York University School of Medicine, New York, NY 10016, USA
2 Dermatology, 2Pharmacology and 2Urology, 2Kaplan Comprehensive Cancer Center, New York University School of Medicine, New York, NY 10016, USA
* Author for correspondence (e-mail: kong{at}saturn.med.nyu.edu)
Accepted 20 June 2003
![]() |
Summary |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
Key words: Urothelium, Uroplakin, Electron cryo-microscopy, Plasma membrane, Permeability barrier, Tetraspanin
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
Highly purified bovine urothelial plaques contain four major uroplakins (UPs), i.e., UP Ia (27 kDa), Ib (28 kDa), II (15 kDa) and III (47 kDa), which have been conserved during mammalian evolution (Wu et al., 1990; Yu et al., 1990
; Wu and Sun, 1993
; Lin et al., 1994
; Wu et al., 1994
; Yu et al., 1994
). The closely related UP Ia and Ib have four transmembrane domains connecting one large and one small luminal loop, and belong to the `tetraspanin' family (Yu et al., 1994
; Hemler, 2001
). Members of this family include CD9, CD81, CD82 and CD151, which interact with integrins, B cell receptor and other signaling membrane proteins, and play roles in cell adhesion, cell motility and growth regulation (for reviews, see Maecker et al., 1997
; Boucheix and Rubinstein, 2001
; Hemler, 2001
). UP Ia and Ib interact preferentially with UP II and III, respectively (Wu et al., 1995
; Liang et al., 2001
; Tu et al., 2002
). With the exception of uroplakin III that has a relatively long cytoplasmic domain of about 50 amino acids, the three other uroplakins have extremely small cytoplasmic domains. It has been suggested that the extracellular domains of uroplakins interact tightly with one another forming the extracellular portion of the 16 nm particle characteristic of the urothelial apical surface, while the cytoplasmic tail of uroplakin III is somehow involved in mediating membrane-cytoskeletal interaction (Yu et al., 1994
).
Studies of negatively stained urothelial plaques by electron microscopy (EM) coupled with image processing showed that each 16 nm urothelial plaque particle consists of 6 inner and 6 outer subdomains interconnected to form a `twisted ribbonlike' structure (Hicks and Ketterer, 1969; Vergara et al., 1969
; Brisson and Wade, 1983
; Taylor and Robertson, 1984
; Walz et al., 1995
; Min et al., 2002
). The lipid-embedded domain of the 16 nm particle was visualized by freeze fracture and electron cryo microscopy (cryo-EM), which revealed a transmembrane structure penetrating the lipid bilayer (Staehelin et al., 1972
; Kachar et al., 1999
; Oostergetel et al., 2001
). Although earlier EM studies suggested that the cytoplasmic side of the plaque was smooth, atomic force microscopy studies revealed circular protrusions on the cytoplasmic surface of urothelial plaques (Min et al., 2002
), consistent with the current understanding that all uroplakin subunits are integral membrane proteins (Yu et al., 1994
; Sun et al., 1999
).
To better understand the biological functions of urothelial plaques, we have determined the three-dimensional (3D) structure of mouse urothelial 16 nm particles to 10 Å resolution using electron cryo microscopy, which allows the visualization of the entire uroplakin particle including its transmembrane domains. Our results enabled us to construct a urothelial plaque model suggesting the association of individual uroplakin pairs with specific subdomains of the 16 nm particle, and a possible structural basis of urothelial permeability barrier function.
![]() |
Materials and Methods |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
Image recording and processing
Micrographs were taken at a magnification of 50,000x under low-dose conditions: only those urothelial plaques greater than 0.5 µm in diameter were imaged. After each exposure, the urothelial plaque was examined using a CCD camera to ensure that the plaque was single layered. For 3D reconstruction, images of up to 50° tilt angle were taken. For image processing, the micrographs were first screened by optical diffraction to select the best regions that yielded the highest resolution diffractions. Micrographs with diffraction spots no higher than 15 Å resolution were discarded. The selected electron micrographs were then digitized using a ZEISS SCAI scanner at a step size of 14 µm, which corresponded to 2.8 Å in the crystal. A total of 45 images were corrected for long-range disorder, merged, averaged and the 3D density map was calculated (only structural factors up to 10 Å resolution were included) using MRC and CCP4 software suites (Henderson et al., 1990; CCP4, 1994
; Crowther et al., 1996
). The density map was visualized using program O (Jones et al., 1991
) and the figures were rendered with Pov-Ray. Portions of this work have been reported previously in an abstract at the 41st American Society for Cell Biology Annual Meeting, in December 2001, in Washington, DC.
![]() |
Results and Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
|
|
|
|
Dimension and architecture of the 16 nm particle
When viewed from the side, the 16 nm particle could be divided into four zones (Fig. 4C): the bottom cytoplasmic zone (C), the transmembrane zone (TM), the trunk zone (TK), and the top joint zone (J). We determined the total height of the urothelial particle to be 12 nm, which is consistent with previously reported values of 12-13 nm based on thin-section electron microscopy (Staehelin et al., 1972
; Hicks et al., 1974
; Robertson and Vergara, 1980
), 13.2 nm based on cryo-EM (Oostergetel et al., 2001
), and 12.5 nm based on atomic force microscopy (Min et al., 2002
) (unpublished data). Our recent atomic force microscopy data indicated that the extracellular portion of the urothelial particle is 6.5 nm in height (Min et al., 2002
) (Fig. 4C). This value also compares favorably with reported values of 5 nm (Brisson and Wade, 1983
; Walz et al., 1995
) or 5.7 nm based on 3D reconstruction of negatively stained images (Taylor and Robertson, 1984
); or 6 nm (Hicks et al., 1974
) or 6.5 nm (Robertson and Vergara, 1980
) based on thin-section electron microscopy. Finally, our atomic force microscopy data indicate that there is a cytoplasmic protrusion of 0.5 nm (Min et al., 2002
). Taken together, these data suggest an
5 nm transmembrane domain (Fig. 4C), which is considerably thicker than an ordinary phospholipid-type lipid bilayer [usually
3.5-4 nm (van Meer and Lisman, 2002
)]. However, this thickness is consistent with a lipid bilayer of sphingolipids [usually 4.5-5.5 nm (van Meer and Lisman, 2002
)], which are known to be enriched in urothelial plaques (see below). The assignment of a 5 nm transmembrane domain, as shown in Fig. 4C, puts a constricted zone, which can be seen in Fig. 4C (open arrowhead), below the exoplasmic surface of the lipid bilayer. Whether this constriction should coincide with the exoplasmic surface (i.e., whether the lipid bilayer thickness should be less than the currently assigned 5 nm) so that the narrow neck can serve as a `hinge' contributing to the recently observed flexibility of the urothelial particle (Kachar et al., 1999
) needs to be further studied.
Each outer subdomain was connected to the closest neighboring inner subdomain at the top via a horizontal `joint' (Fig. 4A,D), forming one of the six inverted U-shaped `subunits' (for a top view of a subunit outlined in blue see Fig. 4A; for side view see Fig. 4D), which most likely represent the basic building blocks of the 16 nm particle (Warren and Hicks, 1978). However, the inner subdomain of each subunit formed relatively thin contacts with the inner subdomains of the two neighboring subunits (Fig. 4E; double arrowhead). The transmembrane zones of both inner and outer subdomains were cylindrical in shape, and were both nearly perpendicular to the membrane plane (Fig. 4C-E).
Different levels of subdomain and subunit interactions
As mentioned earlier, uroplakins Ia and Ib belong to the tetraspanin gene family (Yu et al., 1994; Maecker et al., 1997
; Boucheix and Rubinstein, 2001
; Hemler, 2001
). Many tetraspanin proteins can form networks (or `webs') on the cell surface by interacting with other tetraspanins as well as some single transmembrane-domained proteins involved in signal transduction (Boucheix and Rubinstein, 2001
). With the exception of CD81 whose large extracellular loop has been solved to atomic resolution (Kitadokoro et al., 2001
), relatively little is known about the structure of tetraspanin complexes. Thus structural analysis of uroplakin tetraspanin complexes that naturally form 2D crystals provides a unique opportunity to better understand how tetraspanins interact with each other and with other single transmembrane-domained integral membrane proteins.
Our data indicate that there are probably four levels of interactions involved in the formation of a crystalline uroplakin network. (i) The first level of interaction involves the association of the tetraspanin uroplakins Ia and Ib with their partner uroplakins II and III, respectively, to form a heterodimer (Wu et al., 1995; Liang et al., 2001
; Tu et al., 2002
). As will be discussed later, available EM localization and STEM data suggest that UPIa/II and UPIb/III uroplakin pairs are associated with the inner and outer subdomains, respectively (Fig. 5J). Within each subdomain, the two members of the uroplakin pair appear to interact through both their extracellular and transmembrane domains (Fig. 4D,E, Fig. 5I,J). (ii) In the next level of interaction, the tip of each inner subdomain is connected to that of a neighboring outer subdomain through an extracellular `joint' to form an inverted U-shaped subunit (Fig. 4D). The joint probably consists of mainly the N-terminal moieties of the single transmembranedomained uroplakins, i.e., UPII and UPIII, because the joint occupies the top 3 nm of the 12 nm tall particle, but even the larger extracellular loop of UP Ia and Ib extents to only about 9 nm (including the transmembrane domains) according to structural modeling (data not shown) [see also Bienstock and Barrett (Bienstock and Barrett, 2001
) for the structural model of CD82, another tetraspanin also known as KAI-1]. (iii) On the next level, each inverted U-shaped subunit is associated with its neighboring subunit via a small connection located below the exoplasmic leaflet of the lipid bilayer (Fig. 4A,E; double arrowhead); these small connections link the 6 subunits together to form a 16 nm particle (Fig. 4A). Although these inter-subunit connections seem much less extensive when compared with the inter-subdomain interactions mediated by the joint, they appear to form a complete ring that can potentially hinder the intermixing of lipids located in the central hole and those in the interparticle region (see below). (iv) Finally, the 16 nm particles are packed hexagonally to form a crystalline plaque (Fig. 4B). This inter-particle interaction appears to occur at the 2-fold axes (Fig. 2), consistent with earlier suggestions by Walz et al. (Walz et al., 1995
) and Kachar et al. (Kachar et al., 1999
). Overall, these considerations suggest that the interactions between the uroplakins to form a subdomain is probably quite extensive; the interactions between the inner and outer subdomains within a subunit are moderately extensive, while the inter-subunit and inter-particle interactions are less extensive (Figs 4 and 5).
A possible tunnel
The density map of the 16 nm particle contoured at level 1.5 revealed the possible existence of a transmembrane tunnel in the outer subdomain (arrowheads in Fig. 5). Although the inner subdomain appeared to also have a tunnel, it did not traverse the entire height of the subdomain at the 1.5
contour level. The outer subdomain tunnel had an extracellular opening located at the junction between the top `joint' and the `trunk' (arrowheads in Fig. 5B), and an intracellular opening located in the `cytoplasmic zone' (Fig. 5B,E-H). These two openings were relatively narrow but they led to a chamber in the center of the trunk zone (Fig. 5B). The possible existence of a transmembrane tunnel through the urothelial plaque particle, and its functional implications need to be further investigated.
Uroplakin-lipid interaction as a possible mechanism for the permeability barrier function of urothelial plaque
As mentioned earlier, a key issue in urothelial biology is the structural basis for the extraordinary permeability barrier of urothelial plaques. It seems likely that several factors contribute to this barrier function. First, an interesting feature of the uroplakin particle is the presence of a large central `hole' (Fig. 4A,B). Although previous negative staining data could not rule out the possible existence of a stain-excluding region in the center of this hole (Taylor and Robertson, 1984; Walz et al., 1995
), our cryo-EM data clearly established the absence of protein mass in this area (see also Oostergetel et al., 2001
). This means that, despite a prominent protein lattice appearance, the bulk of the plaque surface (
62%) is occupied by lipids (Fig. 4) (see also Hicks et al., 1974
). In this regard, it is interesting to note that the lipids of highly purified urothelial plaques (that have not been treated with detergents) are unusually rich in sphingolipids and cholesterol (Vergara et al., 1974
; Stubbs et al., 1979
; Hu et al., 2002
), which favor an ordered lipid structure and possibly microdomain formation (Simons and van Meer, 1988
; Simons and Ikonen, 1997
; Brown and London, 2000
). Second, and importantly, our finding that the six inner subdomains of the 16 nm particle are interconnected to form a complete ring that is located either slightly below, or coincide with, the exoplasmic surface (Fig. 4E and Fig. 5F) raises the possibility that the lipids of the exoplasmic surface may be physically segregated, thus further enhancing the formation of various lipid microdomains. Third, the crystalline lattice of uroplakin proteins may promote an organized state and impose structural constraints on the freedom of movement of the lipid molecules thus greatly reducing membrane fluidity, which has been shown to correlate with the membrane permeability to water and other solutes (Lande et al., 1995
). We therefore propose that the crystalline lattice of the uroplakins, through its interactions with specialized lipids, may play an important role in the formation of the remarkable permeability barrier of urothelial plaques. This conclusion is supported by our recent finding that genetic ablation of the uroplakin III gene results in much smaller plaques [in which UPIII is presumably replaced by its minor isoform IIIb (Deng et al., 2002
)] and in compromised functioning of the permeability barrier (Hu et al., 2000
).
The uroplakin structure as described here (Fig. 4) also has implications on the possibly asymmetric contributions by the two leaflets of the urothelial plaque to the functioning of the permeability barrier. Zeidel and co-workers have shown that the reconstituted model exoplasmic membrane of MDCK cells is much more effective as a permeability barrier to solutes and ammonia than the reconstituted cytoplasmic membrane (Hill and Zeidel, 2000) suggesting that, in this case, the two leaflets of a membrane bilayer, with different lipid compositions, can function as independent permeability barriers (Negrete et al., 1996b
; Hill et al., 1999
; Krylov et al., 2001
). Our finding that the portions of the uroplakin particle that are in contact with the two leaflets of the urothelial plaque are structurally distinct (Fig. 4C-E) is likely to favor asymmetric lipid composition of the two leaflets, which may contribute differently to the permeability barrier function of the urothelial plaques.
Possible association of uroplakin pairs Ia/II and Ib/III with the inner and outer subdomains, respectively, of the 16 nm particle
A better understanding of urothelial plaque function requires the localization of individual uroplakins. Recent data indicate that the four uroplakins form two pairs consisting of uroplakins Ia/II and Ib/III, based on data from chemical crosslinking (Wu et al., 1995), ion exchanger isolation of heterodimer complexes (Liang et al., 2001
), genetic ablation of the uroplakin III gene (Hu et al., 2000
) and transient transfection studies (Deng et al., 2002
; Tu et al., 2002
). With regard to the uroplakin composition of the inner and outer subdomains of the 16 nm particle, STEM measurements indicate a total protein mass of 645 kDa per 16 nm particle, or
107 kDa of protein per each of the 6 subunits [each in turn contains an inner and an outer subdomain (Walz et al., 1995
)]. This number is in excellent agreement with the total mass of the two uroplakin pairs (27 kDa (UPIa) + 15 kDa (UPII) + 28 kDa (UPIb) + 47 kDa (UPIII)=117 kDa). In this regard, it is interesting that the transmembrane zone of each subdomain, as depicted in Fig. 5H, can indeed accommodate about 5 transmembrane helices (one tetraspanin plus one single-transmembrane domained UPII or UPIII; Fig. 5I and data not shown). Since we recently showed that uroplakin Ia is associated with the inner subdomains of the 16 nm particle (Min et al., 2002
), these results, taken together, raise the possibility that uroplakin pairs Ia/II and Ib/III are associated with the inner and outer subdomains, respectively (Fig. 5J). Additional localization studies are underway to test this hypothesis.
Conformational changes of uroplakin particles and perspectives
Although urothelial plaque has been described as a `rigid-looking' structure based on its regular, curved appearance in vertical sections by TEM (Fig. 1A), existing data suggest that the 16 nm particle is actually quite flexible and can undergo major conformational changes (Kachar et al., 1999). Consistent with this concept, our data indicate that the uroplakin particle is a remarkably hollow structure (Fig. 4). While each of the 6 inner subdomains is connected to its neighboring outer subdomain at the distal end (top) via a joint (Fig. 4D), relatively little contact exists among the neighboring subunits (Fig. 4E). It would be interesting to determine whether the two subdomains, which are parallel to each other and nearly perpendicular to the membrane, can twist against each other leading to conformational change or movement of the transmembrane domains (Fig. 6). Additional studies of the structure and function of urothelial plaques should shed light on whether such conformational changes can occur and whether such changes play a role in urothelial signal transduction upon bladder stretching and bacterial binding.
|
![]() |
Acknowledgments |
---|
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
Agard, D. A. (1983). A least-squares method for determining structure factors in three-dimensional tilted-view reconstructions. J. Mol. Biol. 167, 849-852.[Medline]
Bienstock, R. J. and Barrett, J. C. (2001). KAI1, a prostate metastasis suppressor: prediction of solvated structure and interactions with binding partners; integrins, cadherins, and cell-surface receptor proteins. Mol. Carcinogen. 32, 139-153.[CrossRef][Medline]
Boucheix, C. and Rubinstein, E. (2001). Tetraspanins. Cell. Mol. Life Sci. 58, 1189-1205.[Medline]
Brisson, A. and Wade, R. H. (1983). Three-dimensional structure of luminal plasma membrane protein from urinary bladder. J. Mol. Biol. 166, 21-36.[Medline]
Brown, D. A. and London, E. (2000). Structure and function of sphingolipidand cholesterol-rich membrane rafts. J. Biol. Chem. 275, 17221-17224.
CCP4 (1994). The CCP4 suite: programs for protein crystallography. Acta Cryst. D50, 760-763.
Chang, A., Hammond, T. G., Sun, T. T. and Zeidel, M. L. (1994). Permeability properties of the mammalian bladder apical membrane. Am. J. Physiol. 267, C1483-C1492.[Medline]
Crowther, R. A., Henderson, R. and Smith, J. M. (1996). MRC image processing programs. J. Struct. Biol. 116, 9-16.[CrossRef][Medline]
Deng, F. M., Liang, F. X., Tu, L., Resing, K. A., Hu, P., Supino, M., Hu, C. C., Zhou, G., Ding, M., Kreibich, G. et al. (2002). Uroplakin IIIb, a urothelial differentiation marker, dimerizes with uroplakin Ib as an early step of urothelial plaque assembly. J. Cell Biol. 159, 685-694.
Hagberg, L., Jodal, U., Korhonen, T. K., Lidin-Janson, G., Lindberg, U. and Svanborg Eden, C. (1981). Adhesion, hemagglutination, and virulence of Escherichia coli causing urinary tract infections. Infect. Immun. 31, 564-570.[Medline]
Hemler, M. E. (2001). Specific tetraspanin functions. J. Cell Biol. 155, 1103-1108.
Henderson, R., Baldwin, J. M., Ceska, T. A., Zemlin, F., Beckmann, E. and Downing, K. H. (1990). Model for the structure of bacteriorhodopsin based on high-resolution electron cryo-microscopy. J. Mol. Biol. 213, 899-929.[Medline]
Hicks, R. M. (1975). The mammalian urinary bladder: an accommodating organ. Biol. Rev. Camb. Philos. Soc. 50, 215-246.[Medline]
Hicks, R. M. and Ketterer, B. (1969). Hexagonal lattice of subunits in the thick luminal membrane of the rat urinary bladder. Nature 224, 1304-1305.[Medline]
Hicks, R. M., Ketterer, B. and Warren, R. C. (1974). The ultrastructure and chemistry of the luminal plasma membrane of the mammalian urinary bladder: a structure with low permeability to water and ions. Philos. Trans. R. Soc. London. Ser. B 268, 23-38.
Hill, W. G., Rivers, R. L. and Zeidel, M. L. (1999). Role of leaflet asymmetry in the permeability of model biological membranes to protons, solutes, and gases. J. Gen. Physiol. 114, 405-414.
Hill, W. G. and Zeidel, M. L. (2000). Reconstituting the barrier properties of a water-tight epithelial membrane by design of leaflet-specific liposomes. J. Biol. Chem. 275, 30176-30185.
Hooton, T. M. and Stamm, W. E. (1997). Diagnosis and treatment of uncomplicated urinary tract infection. Infect. Disease Clinics North America 11, 551-81.
Hu, P., Deng, F. M., Liang, F. X., Hu, C. M., Auerbach, A. B., Shapiro, E., Wu, X. R., Kachar, B. and Sun, T. T. (2000). Ablation of uroplakin III gene results in small urothelial plaques, urothelial leakage, and vesicoureteral reflux. J. Cell Biol. 151, 961-972.
Hu, P., Meyers, S., Liang, F. X., Deng, F. M., Kachar, B., Zeidel, M. L. and Sun, T. T. (2002). Role of membrane proteins in permeability barrier function: uroplakin ablation elevates urothelial permeability. Am. J. Physiol. Renal Physiol. 283, F1200-F1207.
Johnson, J. R. (1991). Virulence factors in Escherichia coli urinary tract infection. Clin. Microbiol. Rev. 4, 80-128.[Medline]
Jones, T. A., Zou, J. Y., Cowan, S. W. and Kjeldgaad, M. (1991). Improved methods for building protein models in electron density maps and the location of errors in these models. Acta Cryst. A47, 110-119.
Kachar, B., Liang, F., Lins, U., Ding, M., Wu, X. R., Stoffler, D., Aebi, U. and Sun, T. T. (1999). Three-dimensional analysis of the 16 nm urothelial plaque particle: luminal surface exposure, preferential head-to-head interaction, and hinge formation. J. Mol. Biol. 285, 595-608.[CrossRef][Medline]
Kitadokoro, K., Bordo, D., Galli, G., Petracca, R., Falugi, F., Abrignani, S., Grandi, G. and Bolognesi, M. (2001). CD81 extracellular domain 3D structure: insight into the tetraspanin superfamily structural motifs. EMBO J. 20, 12-18.
Koss, L. G. (1969). The asymmetric unit membranes of the epithelium of the urinary bladder of the rat. An electron microscopic study of a mechanism of epithelial maturation and function. Lab. Invest. 21, 154-168.[Medline]
Krylov, A. V., Pohl, P., Zeidel, M. L. and Hill, W. G. (2001). Water permeability of asymmetric planar lipid bilayers: leaflets of different composition offer independent and additive resistances to permeation. J. Gen. Physiol. 118, 333-340.
Lande, M. B., Donovan, J. M. and Zeidel, M. L. (1995). The relationship between membrane fluidity and permeabilities to water, solutes, ammonia, and protons. J. Gen. Physiol. 106, 67-84.[Abstract]
Langermann, S., Palaszynski, S., Barnhart, M., Auguste, G., Pinkner, J. S., Burlein, J., Barren, P., Koenig, S., Leath, S., Jones, C. H. et al. (1997). Prevention of mucosal Escherichia coli infection by FimH-adhesin-based systemic vaccination. Science 276, 607-611.
Lewis, S. A. (2000). Everything you wanted to know about the bladder epithelium but were afraid to ask. Am. J. Physiol. Renal Physiol. 278, F867-F874.
Lewis, S. A. and de Moura, J. L. (1982). Incorporation of cytoplasmic vesicles into apical membrane of mammalian urinary bladder epithelium. Nature 297, 685-688.[Medline]
Liang, F., Kachar, B., Ding, M., Zhai, Z., Wu, X. R. and Sun, T. T. (1999). Urothelial hinge as a highly specialized membrane: detergent-insolubility, urohingin association, and in vitro formation. Differentiation 65, 59-69.[CrossRef][Medline]
Liang, F. X., Riedel, I., Deng, F. M., Zhou, G., Xu, C., Wu, X. R., Kong, X. P., Moll, R. and Sun, T. T. (2001). Organization of uroplakin subunits: transmembrane topology, pair formation and plaque composition. Biochem. J. 355, 13-18.[CrossRef][Medline]
Lin, J. H., Wu, X. R., Kreibich, G. and Sun, T. T. (1994). Precursor sequence, processing, and urothelium-specific expression of a major 15-kDa protein subunit of asymmetric unit membrane. J. Biol. Chem. 269, 1775-1784.
Maecker, H. T., Todd, S. C. and Levy, S. (1997). The tetraspanin superfamily: molecular facilitators. FASEB J. 11, 428-442.
Min, G., Stolz, M., Zhou, G., Liang, F., Sebbel, P., Stoffler, D., Glockshuber, R., Sun, T. T., Aebi, U. and Kong, X. P. (2002). Localization of uroplakin Ia, the urothelial receptor for bacterial adhesin FimH, on the six inner domains of the 16 nm urothelial plaque particle. J. Mol. Biol. 317, 697-706.[CrossRef][Medline]
Minsky, B. D. and Chlapowski, F. J. (1978). Morphometric analysis of the translocation of luminal membrane between cytoplasm and cell surface of transitional epithelial cells during the expansion-contraction cycles of mammalian urinary bladder. J. Cell Biol. 77, 685-697.[Abstract]
Mulvey, M. A., Lopez-Boado, Y. S., Wilson, C. L., Roth, R., Parks, W. C., Heuser, J. and Hultgren, S. J. (1998). Induction and evasion of host defenses by type 1-piliated uropathogenic Escherichia coli. Science 282, 1494-1497.
Mulvey, M. A., Schilling, J. D., Martinez, J. J. and Hultgren, S. J. (2000). From the Cover: Bad bugs and beleaguered bladders: Interplay between uropathogenic Escherichia coli and innate host defenses. Proc. Natl. Acad. Sci. USA 97, 8829-8835.
Negrete, H. O., Lavelle, J. P., Berg, J., Lewis, S. A. and Zeidel, M. L. (1996a). Permeability properties of the intact mammalian bladder epithelium. Am. J. Physiol. 271, F886-F894.[Medline]
Negrete, H. O., Rivers, R. L., Goughs, A. H., Colombini, M. and Zeidel, M. L. (1996b). Individual leaflets of a membrane bilayer can independently regulate permeability. J. Biol. Chem. 271, 11627-11630.
Oostergetel, G. T., Keegstra, W. and Brisson, A. (2001). Structure of the major membrane protein complex from urinary bladder epithelial cells by cryo-electron crystallography. J. Mol. Biol. 314, 245-252.[CrossRef][Medline]
Porter, K. R., Kenyon, K. and Badenhausen, S. (1967). Specialization of the unit membrane. Protoplasma 63, 262-274.[Medline]
Robertson, J. D. and Vergara, J. (1980). Analysis of the structure of intramembrane particles of the mammalian urinary bladder. J. Cell Biol. 86, 514-528.[Abstract]
Schilling, J. D. and Hultgren, S. J. (2002). Recent advances into the pathogenesis of recurrent urinary tract infections: the bladder as a reservoir for uropathogenic Escherichia coli. Int. J. Antimicrob. Agents 19, 457-460.[CrossRef][Medline]
Simons, K. and Ikonen, E. (1997). Functional rafts in cell membranes. Nature 387, 569-572.[CrossRef][Medline]
Simons, K. and van Meer, G. (1988). Lipid sorting in epithelial cells. Biochemistry 27, 6197-6202.[Medline]
Staehelin, L. A., Chlapowski, F. J. and Bonneville, M. A. (1972). Lumenal plasma membrane of the urinary bladder. I. Three-dimensional reconstruction from freeze-etch images. J. Cell Biol. 53, 73-91.
Stubbs, C. D., Ketterer, B. and Hicks, R. M. (1979). The isolation and analysis of the luminal plasma membrane of calf urinary bladder epithelium. Biochim. Biophys. Acta 558, 58-72.[Medline]
Sun, T. T., Liang, F. X. and Wu, X. R. (1999). Uroplakins as markers of urothelial differentiation. Adv. Exp. Med. Biol. 462, 7-18.[Medline]
Svanborg, C. and de Man, P. (1987). Bacterial virulence in urinary tract infection. Infect. Disease Clinics North America 1, 731-750.
Taylor, K. A. and Robertson, J. D. (1984). Analysis of the three-dimensional structure of the urinary bladder epithelial cell membranes. J. Ultrastruct. Res. 87, 23-30.[Medline]
Tu, L., Sun, T. T. and Kreibich, G. (2002). Specific heterodimer formation is a prerequisite for uroplakins to exit from the endoplasmic reticulum. Mol. Biol. Cell 13, 4221-4230.
Unger, V. M. and Schertler, G. F. (1995). Low resolution structure of bovine rhodopsin determined by electron cryo-microscopy. Biophys. J. 68, 1776-1786.[Abstract]
van Meer, G. and Lisman, Q. (2002). Sphingolipid transport: rafts and translocators. J. Biol. Chem. 277, 25855-25858.
Vergara, J., Longley, W. and Robertson, J. D. (1969). A hexagonal arrangement of subunits in membrane of mouse urinary bladder. J. Mol. Biol. 46, 593-596.[Medline]
Vergara, J., Zambrano, F., Robertson, J. D. and Elrod, H. (1974). Isolation and characterization of luminal membranes from urinary bladder. J. Cell Biol. 61, 83-94.
Walz, T., Haner, M., Wu, X. R., Henn, C., Engel, A., Sun, T. T. and Aebi, U. (1995). Towards the molecular architecture of the asymmetric unit membrane of the mammalian urinary bladder epithelium: a closed "twisted ribbon" structure. J. Mol. Biol. 248, 887-900.[CrossRef][Medline]
Wang, D. N. and Kuhlbrandt, W. (1991). High-resolution electron crystallography of light-harvesting chlorophyII a/b-protein complex in three different media. J. Mol. Biol. 217, 691-699.[Medline]
Warren, R. C. and Hicks, R. M. (1978). Chemical dissection and negative staining of the bladder luminal membrane. J. Ultrastruct. Res. 64, 327-340.[Medline]
Wu, X. R., Lin, J. H., Walz, T., Haner, M., Yu, J., Aebi, U. and Sun, T. T. (1994). Mammalian uroplakins. A group of highly conserved urothelial differentiation-related membrane proteins. J. Biol. Chem. 269, 13716-13724.
Wu, X. R., Manabe, M., Yu, J. and Sun, T. T. (1990). Large scale purification and immunolocalization of bovine uroplakins I, II, and III. Molecular markers of urothelial differentiation. J. Biol. Chem. 265, 19170-19179.
Wu, X. R., Medina, J. J. and Sun, T. T. (1995). Selective interactions of UPIa and UPIb, two members of the transmembrane 4 superfamily, with distinct single transmembrane-domained proteins in differentiated urothelial cells. J. Biol. Chem. 270, 29752-29759.
Wu, X. R. and Sun, T. T. (1993). Molecular cloning of a 47 kDa tissuespecific and differentiation-dependent urothelial cell surface glycoprotein. J. Cell Sci. 106, 31-43.
Wu, X. R., Sun, T. T. and Medina, J. J. (1996). In vitro binding of type 1-fimbriated Escherichia coli to uroplakins Ia and Ib: relation to urinary tract infections. Proc. Natl. Acad. Sci. USA 93, 9630-9635.
Yu, J., Lin, J. H., Wu, X. R. and Sun, T. T. (1994). Uroplakins Ia and Ib, two major differentiation products of bladder epithelium, belong to a family of four transmembrane domain (4TM) proteins. J. Cell Biol. 125, 171-182.[Abstract]
Yu, J., Manabe, M., Wu, X. R., Xu, C., Surya, B. and Sun, T. T. (1990). Uroplakin I: a 27-kD protein associated with the asymmetric unit membrane of mammalian urothelium. J. Cell Biol. 111, 1207-1216.[Abstract]
Zhou, G., Mo, W. J., Min, G. W., Sebbel, P., Neubert, T. A., Glockshuber, R., Wu, X. R., Sun, T. T. and Kong, X. P. (2001). Uroplakin Ia is the urothelial receptor for uropathogenic Escherichia coli: evidence from in vitro FimH binding. J. Cell Sci. 114, 4095-4103.[Medline]
Related articles in JCS: