Structures of collagen IV globular domains: insight into associated pathologies, folding and network assembly

Abstract

Crystal structures of the noncollagenous domains of the collagen type IV α1–α5 chains provide structural insight into Alport’s syndrome (a genetic kidney disorder) and the first views of the components of Goodpasture’s autoimmune disease epitopes. These structures define key folding motifs for collagen IV scaffolding of basement membranes, support the operation of mechanisms for restricting the self-assembly of noncollagenous domains, and raise the possibility that homohexamers of α1 or α3 chains could occur in nature.

A chloride ring is an ancient evolutionary innovation mediating the assembly of the collagen IV scaffold of basement membranes

“…Group 1 has been previously identified (18) and includes six chloride ions (16). Group 2 has been recently suggested and also includes six chloride ions (19). Several factors support the Cl − nature for the observed electron densities (Fig.…”

“…Re-analysis of structural data pointed to a possibility that sites originally assigned to K + are rather occupied by an additional six Cl − . Very recently, the same conclusion was reached based on structural data of different NC1 hexamers assembled from recombinant polypeptides (19). The number of ions at the trimer–trimer interface of α121 NC1 hexamers in reported structures varies depending on protein source, preparation, crystallization conditions, and resolution, where 6, 8, 11, 12, and 14 ions per hexamer were identified (18–21).…”

“…Very recently, the same conclusion was reached based on structural data of different NC1 hexamers assembled from recombinant polypeptides (19). The number of ions at the trimer–trimer interface of α121 NC1 hexamers in reported structures varies depending on protein source, preparation, crystallization conditions, and resolution, where 6, 8, 11, 12, and 14 ions per hexamer were identified (18–21). To determine the number and positions of Cl − ions involved into stabilization of the NC1 hexamer, here we purposely purified and crystallized the sc121 NC1-trimer in the presence of high chloride concentration to mimic natural extracellular Cl − content.…”

“…Our recent studies showed that the high concentration of Cl − ions on the outside of cells signals protomer oligomerization and that Cl − ions bound to NC1 trimers trigger a conformational switch, which mediates protomer oligomerization (16). Importantly, our recent studies of the crystal structures of α121 NC1 hexamers revealed an additional group of six Cl − ions that are embedded at the trimer–trimer interface (19), indicating a role for these ions in hexamer assembly.…”

Collagen IVα345 dysfunction in glomerular basement membrane diseases. II. Crystal structure of the α345 hexamer

“…of 0.55 to 0.60 Å for α3 and 0.58 Å for α5 ( Table S3 ). Nevertheless, NC1 domains demonstrate sufficient plasticity by forming α2 homotetramer/homo-octamer and α4 homohexamer/homododecamer upon crystallization ( 13 ), although for the price of ∼20% and ∼10% of their inner sequences being unstructured. Superposition of the α4 structure of the α345 trimer with the structured part of α4 in the artefactual α4 homohexamer/homododecamer has r.m.s.d.…”