Prokaryotic Collagen-Like Proteins as Novel Biomaterials

Abstract

Collagens are the major structural component in animal extracellular matrices and are critical signaling molecules in various cell-matrix interactions. Its unique triple helical structure is enabled by tripeptide Gly-X-Y repeats. Understanding of sequence requirements for animal-derived collagen led to the discovery of prokaryotic collagen-like protein in the early 2000s. These prokaryotic collagen-like proteins are structurally similar to mammalian collagens in many ways. However, unlike the challenges associated with recombinant expression of mammalian collagens, these prokaryotic collagen-like proteins can be readily expressed in E. coli and are amenable to genetic modification. In this review article, we will first discuss the properties of mammalian collagen and provide a comparative analysis of mammalian collagen and prokaryotic collagen-like proteins. We will then review the use of prokaryotic collagen-like proteins to both study the biology of conventional collagen and develop a new biomaterial platform. Finally, we will describe the application of Scl2 protein, a streptococcal collagen-like protein, in thromboresistant coating for cardiovascular devices, scaffolds for bone regeneration, chronic wound dressing and matrices for cartilage regeneration.

Keywords: biomaterials; collagen; hydrogel; integrin; integrin-targeting biomaterials; prokaryotic collagen-like protein; streptococcal collagen-like protein.

FIGURE 1

Crystal structure of a collagen peptide with the sequence (PPG)₁₀, accessed from PDB ID: 1K6F. The crystal structure shows the structure of the triple helical collagen. Three individual peptides are shown with green representing the leading strand of collagen, pink representing the middle strand, and blue representing the lagging strand.

FIGURE 2

Domain organization of various eukaryotic and prokaryotic collagens. All numbers in parenthesis below species name and protein name is the accession number for the protein as found in the NCBI Protein database. Numbers below the domains indicate the last residue of that domain. Abbreviations are as follows: NTD = N-terminal Domain, CTD = C-terminal Domain, V = Trimerization Domain, C = C-terminal domain and anchor to cell membrane, N = N-terminal Domain and anchor to cell membrane, CLR = Collagen-like Region.

FIGURE 3

Incorporation of Scl2 proteins into hydrogels as alternative materials to animal-derived collagen matrices. (A) Scl2 protein hydrogel network with varied crosslinking modalities for enhanced gel stability. (B) Hybrid Scl2 hydrogels with the Scl2 protein anchored into a synthetic hydrogel network via a functionalization linker and the different parameters used to modulate hydrogel properties. (C) Different physcial forms of hybrid Scl2 hydrogels used in biomedical applications.

FIGURE 4

Biomedical applications of Scl2-containing biomaterials with targeted integrin interactions. (A) PEG-Scl2 hydrogel coatings of cardiovascular devices to enhance thromboresistance; (B) PEG-Scl2 hydrogel that revealed integrin-mediated hMSC osteogenic differentiation via the MAPK signal pathway (C) Different types of dressings containing Scl2 proteins to enhance chronic wound healing; (D) PEG-Scl2 protein hydrogel with binding sites for chondroitin sulfate and hyaluronic acid to improve cartilage repair.