Identification of unique α4 chain structure and conserved anti-angiogenic activity of α3NC1 type IV collagen in zebrafish

Type IV collagen, the most abundant component of basement membranes, is essential for the formation of the extracellular scaffold that supports tissue architecture and function. Collagen IV is present in all multicellular species, with lower organisms typically possessing two type IV collagen genes, encoding α1 and α2 chains. The human genome encodes for six different type IV collagen genes, α1 to α6 chains. The α chains assemble into trimeric protomers, the building blocks of the type IV collagen network. The detailed evolutionary conservation of type IV collagen network organization remains to be studied. Here we report on the molecular evolution of type IV collagen genes. Specifically, we report on the zebrafish α4 NC1 domain, which, in contrast with its human ortholog, contains an additional cysteine residue and lacks the Met93 and Lys211 residues involved in sulfilimine bond formation between adjacent protomers. This may alter α4 chain interactions with other α chains, as supported by temporal and anatomic expression patterns of collagen IV chains during zebrafish development. Despite the divergence between zebrafish and human α3 NC1 domain (human endogenous inhibitor of angiogenesis, Tumstatin), the zebrafish α3 NC1 domain exhibits conserved anti-angiogenic activity in human endothelial cells. Our work supports that sequence identity, tissue expression, and function of type IV collagen have remained largely conserved between zebrafish and humans, with one possible difference involving the α4 NC1 domain.