Koirala, R. | bioRxiv Science

bioRxiv2026

An Alport variant illuminates the bioactivity of the collagen IV α565- α121 scaffold in Bowman's capsule.

Alport syndrome (AS) is a major cause of chronic kidney failure and affects millions of people worldwide. Pathogenic variants in COL4A3, COL4A4, and COL4A5, which encode the collagen IV 345 scaffold, compromise glomerular basement membrane (GBM) structure and function. However, the molecular mechanisms linking the >5,000 reported variants to disease pathology remain poorly understood. To address this gap, we previously examined a distinctive variant, an 8-amino acid "Z-appendage", added to the NC1 domain of the 3 chain. Knock-in mice carrying this variant developed GBM abnormalities and proteinuria, implicating the NC1 hexamer as a critical determinant of GBM function and suggesting that the hexamer surface contains bioactive sites that may mediate signaling and/or organization of macromolecular complexes. Given that approximately 80% of AS cases are associated with COL4A5 variants, including many within the NC1 hexamer, we asked whether relocating the Z-appendage from the 3 NC1 subunit to the 5 subunit produces similar pathology. Strikingly, Col4a5-Z mice did not develop proteinuria and showed only minor changes in GBM morphology. In contrast, the variant induced marked thickening of Bowmans capsule, accompanied by increased deposition of the collagen IV 121 scaffold, increased fibrillar collagen, and cellular deposits. Structural modeling predicts that the collagen IV 565-121 scaffold bearing two Z-appendages adopts an aberrant secondary structure that may stiffen the scaffold and occlude binding sites. Together, these findings reveal a bioactive role for the collagen IV 565-121 scaffold in the Bowmans capsule basement membrane, with potential implications for other 565-121containing tissues such as the aorta and bladder.

molecular biology↗

bioRxiv2020

Inside-out regulation of E-cadherin conformation and adhesion

Cadherin cell-cell adhesion proteins play key roles in tissue morphogenesis and wound healing. Cadherin ectodomains bind in two conformations, X-dimers and strand-swap dimers, with different adhesive properties. However, the mechanisms by which cells regulate ectodomain conformation are unknown. Cadherin intracellular regions associate with several actin-binding proteins including vinculin, which are believed to tune cell-cell adhesion by remodeling the actin cytoskeleton. Here, we show at the single molecule level, that vinculin association with the cadherin cytoplasmic region allosterically converts weak X-dimers into strong strand-swap dimers, and that this process is mediated by myosin II dependent changes in cytoskeletal tension. We also show that in epithelial cells, [~]70% of apical cadherins exist as strand-swap dimers while the remaining form X-dimers, providing two cadherin pools with different adhesive properties. Our results demonstrate, for the first time, the inside-out regulation of cadherin conformation and establish a mechanistic role for vinculin in this process. SIGNIFICANCE STATEMENTCadherin cell-cell adhesion proteins play key roles in the formation and maintenance of tissues. Their adhesion is carefully regulated to orchestrate complex movement of cells. While cadherin ectodomains bind in two conformations with different adhesive properties, the mechanisms by which cells regulate the conformation (and consequently adhesion) of individual cadherins are unknown. Here, we demonstrate that the association of intracellular vinculin to the cadherin cytoplasmic region, regulates cadherin adhesion by switching ectodomains from a weak binding to the strongly adhesive conformation. In contrast with the prevailing view which suggests that vinculin regulates adhesion solely by remodeling the cytoskeleton, we show that vinculin can directly modulate single cadherin ectodomain conformation and that this process is mediated by changes in cytoskeletal tension.

biophysics↗