Molecular Insights for the Role of Key Residues of Calreticulin in its Binding Activities

Abstract

Calreticulin (CRT) is localized to and has functions in multiple cellular compartments, including cell surface, endoplasmic reticulum, and extracellular matrix (FASEB J. 24: 665- 683, 2010). Mutagenesis studies have identified several residues on a concave β-sheet surface of CRT critical for CRT binding to carbohydrate and other proteins/peptides (J. Biol. Chem. 285: 38612-20, 2010). How the mutations of these key residues in CRT affect the conformation and dynamical motion of CRT, further influencing CRT binding activities remain unknown. In this study, we investigated the effect of several key point mutations on the conformational and dynamical motion changes of CRT via atomistic molecular dynamics simulations. The CRT structure is obtained based on the crystal structure of the globular lectin domain and partial P-domain of CRT, and the NMR structure of P-domain (flexible arm domain). Results from this study show that the mutations of the key residues of CRT result in the changes in the protein's local backbone flexibility and some of the point mutations cause significant changes of the relatively position and orientation between the CRT lectin and P-domains. Within the β-strands in CRT's lection domain, mutant-induced secondary structural changes, including the changes in the residues of β-strand occupancy, number of H-bonds and hydrophobic contacts, are observed. The mutations of the key residues on the concave β-sheet surface of CRT also result in the changes of the solvent accessible surface area, side-chain relative positions and dynamical correlated motions, which could directly affect CRT binding activities. Results from this study provided molecular insight into the effect of the mutations of key residues of CRT on CRT conformational and dynamical motion changes, further influencing CRT binding to carbohydrates and other proteins to signal the important cellular activities.