The ultrafiltration function of the glomerular basement membrane (GBM) of the kidney is impaired in genetic and acquired diseases that affect type IV collagen. The GBM is composed of five (␣1 to ␣5) of the six chains of type IV collagen, organized into an ␣1⅐␣2(IV) and an ␣3⅐␣4⅐␣5(IV) network. In Alport syndrome, mutations in any of the genes encoding the ␣3(IV), ␣4(IV), and ␣5(IV) chains cause the absence of the ␣3⅐␣4⅐␣5 network, which leads to progressive renal failure. In the present study, the molecular mechanism underlying the network defect was explored by further characterization of the chain organization and elucidation of the discriminatory interactions that govern network assembly. The existence of the two networks was further established by analysis of the hexameric complex of the noncollagenous (NC1) domains, and the ␣5 chain was shown to be linked to the ␣3 and ␣4 chains by interaction through their respective NC1 domains. The potential recognition function of the NC1 domains in network assembly was investigated by comparing the composition of native NC1 hexamers with hexamers that were dissociated and reconstituted in vitro and with hexamers assembled in vitro from purified ␣1-␣5(IV) NC1 monomers. The results showed that NC1 monomers associate to form nativelike hexamers characterized by two distinct populations, an ␣1⅐␣2 and ␣3⅐␣4⅐␣5 heterohexamer. These findings indicate that the NC1 monomers contain recognition sequences for selection of chains and protomers that are sufficient to encode the assembly of the ␣1⅐␣2 and ␣3⅐␣4⅐␣5 networks of GBM. Moreover, hexamer formation from the ␣3, ␣4, and ␣5 NC1 monomers required co-assembly of all three monomers, suggesting that mutations in the NC1 domain in Alport syndrome may disrupt the assembly of the ␣3⅐␣4⅐␣5 network by interfering with the assembly of the ␣3⅐␣4⅐␣5 NC1 hexamer.
Glomerular basement membrane (GBM) plays a crucial function in the ultrafiltration of blood plasma by the kidney. This function is impaired in Alport syndrome, a hereditary disorder that is caused by mutations in the gene encoding type IV collagen, but it is not known how the mutations lead to a defective GBM. In the present study, the supramolecular organization of type IV collagen of GBM was investigated. This was accomplished by using pseudolysin (EC 3.4.24.26) digestion to excise truncated triple-helical protomers for structural studies. Two distinct sets of truncated protomers were solubilized, one at 4°C and the other at 25°C, and their chain composition was determined by use of monoclonal antibodies. The 4°C protomers comprise the ␣1
Human Goodpasture syndrome is a lethal form of autoimmune disease that is characterized by pulmonary hemorrhage and glomerulonephritis. The tissue injury is mediated by autoantibodies that bind to glomerular and alveolar basement membrane. The target autoantigen is alpha 3(IV) collagen, one of six genetically distinct chains that comprise type IV collagen, and the epitope is sublocalized to the noncollagenous domain (NC1) of the alpha 3 chain. The present study reports the unique capacity of alpha 3(IV)NC1 dimer from bovine kidney to aberrantly engage the immune system of rabbits to respond to self, mimicking the organ-specific form of the human disease, whereas the other chains of type IV collagen are nonpathogenic. However, alpha 3(IV)NC1 hexamer was nonpathogenic, suggesting the exposure of a pathogenic epitope upon dissociation of hexamer into dimers. Exposure of the pathogenic epitope by infection or organic solvents, events which are thought to precede Goodpasture syndrome, may be the principal factor in the etiology of the disease. The pathogenicity of alpha 3(IV) collagen brings full circle a decade of research that has identified four novel chains (alpha 3-alpha 6) of type IV collagen.
Matrix metalloproteinases (MMPs) are activated in vitro from their precursors (proMMPs) by multiple means such as treatment with proteinases, mercurial compounds, chaotropic agents, sodium dodecyl sulfate, HOCl, and heat. The latency of proMMPs is stabilized by intramolecular interaction of the single cysteine residue in the conserved sequence PRCG(V/N)PD of the propeptide and the zinc atom at the active site. The activation of proMMP-1 (interstitial procollagenase) by multiple treatments has been explained by the "cysteine switch" model, in which the disruption of the Cys-Zn interaction is considered to be critical for activation [Springman, E. B., Angleton, E. L., Birkedal-Hansen, H., & VanWart, H. (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 364-368]. To further test this hypothesis we dissociated the Cys-Zn interaction by specifically modifying Cys-75 of proMMP-3 (prostromelysin 1) with iodoacetamide, (4-aminophenyl)mercuric acetate (APMA), or 5,5'-dithiobis(2-nitrobenzoate) and examined the expression of enzymic activity. The enzymic assays of the modified proMMP-3s against protein and synthetic substrates did not reveal any significant activity. The modified 57-kDa proMMP-3s were stable and did not show spontaneous activation. Activation of the modified proMMP-3s required further treatment with APMA or a proteinase and was accompanied by conversion of the proMMP-3 to a 45-kDa species. Circular dichroism studies of proMMP-3 treated with HgCl2 demonstrated time-dependent conformational changes in proMMP-3 prior to the expression of proteolytic activity and processing of the zymogen to lower molecular weight species. These results indicate that the disruption of the Cys-Zn coordination alone is not sufficient to activate proMMP-3.(ABSTRACT TRUNCATED AT 250 WORDS)
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.