SEMINIFEROUS TUBULE BASEMENT-MEMBRANE - COMPOSITION AND ORGANIZATION OF TYPE-IV COLLAGEN CHAINS, AND THE LINKAGE OF ALPHA-3(IV) AND ALPHA-5(IV) CHAINS

Seminiferous tubule basement membrane (STEM) plays an important role i n spermatogenesis, In the present study, the composition and structura l organization of type IV collagen of bovine STEM was investigated, ST EM was found to be composed of all six a-chains of type IV collagen ba sed upon immunocytochemical and biochemical analysis, The content of a lpha 3(IV) chain (40%) and the alpha 4(IV) chain (18%) was substantial ly higher than in any other basement membrane collagen, The supramolec ular structure of the six alpha(IV) chains was investigated using pseu dolysin (EC 3.4.24.26) digestion to excise triple-helical molecules, s ubsequent collagenase digestion to produce NC1 hexamers and antibody a ffinity chromatography to resolve populations of NC1 hex amers, The he xamers, which reflect specific arrangements of alpha(IV) chains, were characterized for their alpha(IV) chain composition using high perform ance liquid chromatography, two-dimensional electrophoresis, and immun oblotting with alpha(IV) chain-specific antibodies, Three major hexame r populations were found that represent the classical network of the a lpha 1(IV) and alpha 2(IV) chains and two novel networks, one composed of the alpha 1(IV)-alpha 6(IV) chains and the other composed of the a lpha 3(IV)-alpha 6(IV) chains, The results establish a structural link age between the alpha 3(IV) and alpha 5(IV) chains, suggesting a molec ular basis for the conundrum in which mutations in the gene encoding t he alpha 5(IV) chain cause defective assembly of the alpha 3(IV) chain in the glomerular basement membrane of patients with Alport syndrome.