Bacterial collagen-like proteins that form triple-helical structures

Abstract

A large number of collagen-like proteins have been identified in bacteria during the past 10years, principally from analysis of genome databases. These bacterial collagens share the distinctive Gly-Xaa-Yaa repeating amino acid sequence of animal collagens which underlies their unique triple-helical structure. A number of the bacterial collagens have been expressed in Escherichia coli, and they all adopt a triple-helix conformation. Unlike animal collagens, these bacterial proteins do not contain the post-translationally modified amino acid, hydroxyproline, which is known to stabilize the triple-helix structure and may promote self-assembly. Despite the absence of collagen hydroxylation, the triple-helix structures of the bacterial collagens studied exhibit a high thermal stability of 35-39°C, close to that seen for mammalian collagens. These bacterial collagens are readily produced in large quantities by recombinant methods, either in the original amino acid sequence or in genetically manipulated sequences. This new family of recombinant, easy to modify collagens could provide a novel system for investigating structural and functional motifs in animal collagens and could also form the basis of new biomedical materials with designed structural properties and functions.

Keywords: Biomedical material; Collagen; Prokaryote; Recombinant expression; Thermal stability; Triple-helix.

Fig. 1

A pie chart representation of the non-Gly amino acid composition of bacterial collagen-like domains. Only the amino acids at Xaa and Yaa positions were taken into consideration. The groups include: hydrophobic (Val, Ile, Leu, Met, Phe), polar (Ser, Thr, Asn, Gln), charged (Asp, Glu, Lys, Arg, His), small (Gly and Ala) and Pro. The amino acid composition of the α1 chain of human4type I collagens is shown for comparison.

Fig. 2

A diagram of the constructs including A, B, or C fragments of the S. pyogenes Scl2 CL domain, showing the rod-like CL domain, the globular V domain, and a small diamond to represent the His₆-tag at the N terminus. Fragments A, B and C were expressed individually in E. coli, or fused with the V domain to promote trimerization. Each fragment was also tandemly fused to construct a dimer (AA, BB, or CC) or a trimer (AAA, BBB, or CCC) appended to the V domain. Although CCC was successfully expressed it was insoluble (Yu et al. 2011

Fig. 3

A diagram illustrating various substitutions and insertions of functional domains from animal collagens that have been made in S. pyogenes Scl2 constructs, including integrin (Seo et al. 2010; An et al. 2013; Peng et al. 2013); heparin (Peng et al. 2013); fibronectin (An et al. 2013), and MMP-1 (Yu et al. 2012).