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Uroplakin IIIa Uroplakin IIIa, mayor isoform of the dimerization partner of uroplakin Ib, is a members of the uroplakin family. Uroplakins (UPs) are a family of proteins that associate with each other to form plaques on the apical surface of the urothelium, the pseudo-stratified epithelium lining the urinary tract from renal pelvis to the bladder outlet. UPs are classified into 3 types: UPIa and UPIb, UPII, and UPIIIa and IIIb. UPIs are tetraspanins that have four transmembrane domains seperating one large and one small extracellular domain while UPII and UPIIIs are single-pass transmembrane proteins. UPIa and UPIb form specific heterodimers with UPII and UPIII, respectively, which allows them to exit the endoplasmatic rediculum. UPII/UPIa and UPIIIs/UPIb form heterotetramers and six of these tetramers form the 16nm particle, seen in the hexagonal array of the asymmetric unit membrane, which is believed to form a urinary tract barrier. Uroplakins are also believed to play a role during urinary tract morphogenesis. |
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