In this study we consider a finite concentration of oligoglycines and longer oligomers of glycine as a model of the behavior of collapse in intrinsically disordered proteins. The solubility of oligoglycine in water decreases experimentally as its length increases. We consider the solubility limit of Gly<sub>5</sub>. Previous simulation work by our group shows that the solvation free energy of oligoglycine decreases as its length increases from 2 to 5 residues, indicating that solvation becomes more favorable. We find that as the peptide length increases, intermolecular interactions between oligoglycines are favored over interactions between oligoglycine and water, leading to their aggregation i.e. local concentration effects play a significant role in driving oligoglycines to aggregate. This aggregation manifests as a liquid-liquid, second order phase transition. We simulate the behavior of over six hundred short (five residues) oligoglycines in water at varying concentrations in order to understand the structural and thermodynamic changes that occur during aggregation of these short peptides. Thermodynamic signatures of this aggregation of short oligoglycines is remarkably similar to the thermodynamics of folding or collapse of longer oligoglycines in water. We compare the thermodynamics of aggregation of short oligoglycines with the collapse of longer oligoglycines in water in order to understand the thermodynamics of collapse of the longer peptide.

Protein aggregation, collapse, and disorder: Model systems

249th National Meeting (2015)

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