Structural Insights into Protein-Ligand Interactions of Small Leucine Rich Repeat Proteoglycans with a Large Number of Binding Partners: An Overview

Small leucine rich repeat proteoglycans (SLRPs) exist in the extracellular matrix. SLRPs contain tandem arrays of LRRs flanked by cysteine clusters at the both N- and C-termini. The extreme N- and/or C-termini contain low complexity sequences, glycosaminoglycan (GAG) chain and/or sulfated tyrosine residues in some members of SLRPs. The LRR solenoid structure may be divided into four parts consisting of a concave surface, an ascending surface, a convex surface, and a descending surface. SLRPs share many biological functions including collagen fibrillogenesis, signaling, innate immunity, and inflammation through the binding of various ligands. We undertake a comprehensive literature search of publications in order to make a list of ligands of SLRPs. We describe and discuss the interacting sites of SLRPs to binding partners. The protein-ligand interactions occur on not only the concave surface but also the ascending surface and the N- or C-terminal capping regions. In addition, the extreme N- and/or C-terminal regions with the GAG chains or sulfated tyrosine residues participate in ligand-interactions.