Structural basis of homo- and heterotrimerization of collagen I

Abstract

Fibrillar collagen molecules are synthesized as precursors, procollagens, with large propeptide extensions. While a homotrimeric form (three α1 chains) has been reported in embryonic tissues as well as in diseases (cancer, fibrosis, genetic disorders), collagen type I usually occurs as a heterotrimer (two α1 chains and one α2 chain). Inside the cell, the role of the C-terminal propeptides is to gather together the correct combination of three α chains during molecular assembly, but how this occurs for different forms of the same collagen type is so far unknown. Here, by structural and mutagenic analysis, we identify key amino acid residues in the α1 and α2 C-propeptides that determine homo- and heterotrimerization. A naturally occurring mutation in one of these alters the homo/heterotrimer balance. These results show how the C-propeptide of the α2 chain has specifically evolved to permit the appearance of heterotrimeric collagen I, the major extracellular building block among the metazoa.

Broadly conserved roles of TMEM131 family proteins in intracellular collagen assembly and secretory cargo trafficking

“…Both COL1A1 and COL1A2 contain C-terminal domains (C-propeptide) responsible for initial chain trimerization in the ER. The trimerization occurs via a zipper-like mechanism, initiating from the C-propeptide domain of 1/2 (I) in close proximity to ER membranes (10)(11)(12)(13). Although the enzymes responsible for type I collagen modification, extracellular cleavage, and cross-linking have been well described (1,14), how procollagen monomers are recruited to assemble into secretion-competent multimers in the ER remains poorly understood.…”

Collagen assembly and turnover imaged with a CRISPR-Cas9 engineered Dendra2 tag

“…We were careful to select an insertion site that would not disrupt collagen fibril formation. This required the identification of a site in the proa2(I) chain that would not disrupt the C-terminal propeptides (which contain the sites for chain selection 12 ), disrupt removal of the C-propeptides (which is required for fibril formation 13 ), remove the binding sites for fibril formation 14 or alter the repeating Gly-X-Y structure of the collagen molecule 15 ). We reasoned that the only possible site for insertion of Dendra2 was N-terminal of the N-propeptides, i.e.…”

Thrombospondin-1 promotes matrix homeostasis by interacting with collagen and lysyl oxidase precursors and collagen cross-linking sites

“…We also tested binding of TSP1 to recombinant trimers of the collagen C-propeptide domain (C-Pro as shown in Fig. 2C), which drives triple-helix assembly in fibrillar procollagens and also prevents inappropriate fibril formation intracellularly (2,4). We observed concentration-dependent binding of TSP1 to recombinant homotrimers of procollagen 1(I) C-propeptides (CPI) but not to recombinant homotrimers of procollagen 1(III) C-propeptides (CPIII), which share 66% sequence identity with CPI ( Fig.…”

“…Binding of TSP1 to CPI depended on the presence of calcium, which is required for homotrimerization of the C-propeptides ( Fig. 2F) (4,46). Comparison of the concentration dependence of TSP1 binding to CPI, pepsin-digested collagen I, or a recombinant, homotrimeric "mini" procollagen I (rProCOL1A1; this protein includes the N-propeptide, N-telopeptide, the 33 most N-terminal and 33 most C-terminal Gly-Xaa-Yaa repeats, C-telopeptide, and C-propeptide) demonstrated enhanced binding of TSP1 to the latter protein ( Fig.…”

“…This is followed by steps important for stable assembly of the triple helix: posttranslational hydroxylation of lysine and proline residues and glycosylation of lysines (3). The C-propeptide domain guides  chain assembly into procollagen molecules, forming an in-register triple helix and preventing premature intracellular fibril nucleation by restricting lateral packing (4). Upon secretion, the C-propeptide domain is cleaved off mainly by bone morphogenetic protein-1 (BMP-1), and the N-propeptide is cleaved off by a disintegrin and metalloproteinase with thrombospondin motifs 2 (ADAMTS2), generating mature collagen molecules, consisting of the N-and C-telopeptides and the central triple-helical domain, that are competent for fibril assembly.…”