HOW CHARGED RESIDUES INFLUENCE THE THERMAL STABILITY OF COLLAGEN: A STUDY WITH NATURAL AND NON-NATURAL AMINO ACIDS

Abstract

Triple-helical collagens are key structural proteins in mammals. Their ubiquity and diverse functions drive our interest into understanding their behavior at a fundamental level. This thesis describes a reductionist approach using novel collagen-related peptides (CRPs), into which one or more electrical charges have been imparted at known positions. One series of CRPs includes fluorescent pyrene tags at their N-termini, directly adjacent to the charged residues lysine (Lys, K) and glutamic acid (Glu, E). When in close contact, the fluorophores form excimers that emit low-energy light. Monitoring of the excimer intensity shows that nucleation of collagen peptides is critically dependent on the charge location. Another series of CRPs features pH-independent (permanent) positive charge close to the peptide backbone, via a synthetic proline derivative called “Map.” When in close contact, repulsion between Map residues overwhelms the natural tendencies of the peptides to fold. CD and fluorescence investigations into the thermodynamic and kinetic behaviors of these CRPs have been supplemented with computational analyses, to shed light on the deleterious role of charge in trimer formation.