Secondary Structure and Nanomechanical Properties of Proteins

Jonathan Nickels (Oak Ridge National Laboratory)

Protein materials have adapted to meet a huge array of structural needs, from the elasticity of a blood vessel to the rigidity of spider silk. Part of this structural and functional diversity is encoded in the secondary structure of the proteins that make up these materials. I will present an overview of recent work that has been done to investigate the nanomechanical properties of proteins in connection to their secondary structures. A combination of complementary neutron and light scattering measurements have been performed which focused on low frequency collective vibrational dynamics of nine proteins and amino acid mixtures. Of particular interest is the spectral feature known as the boson peak (BP); common to all disordered materials. Our results reveal a systematic trend in local rigidity with secondary structural motifs: disordered proteins appear softer than a-helical proteins; which are softer than β-sheet proteins. I will also present experimental evidence of a connection between secondary structure and the BP from coherent neutron scattering measurements performed on the protein GFP. These measurements confirm a signature of secondary structure in this dynamical feature, but this connection is less than might be expected from the widely accepted analogy of proteins and glassy polymers. Having said this, direct, experimental observations of in phase collective motions from neutron scattering are advancing our understanding of the connections between structure and nanomechanical properties in proteins. This result not only confirms our initial interpretation, connecting the BP feature to secondary structure, but it points the way to next generation of neutron scattering measurements utilizing deuteration schemes for more than the simple suppression of incoherent scattering.

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