PNNL

Abstract

The mechanisms of interface biochemistry are often obscured through ensemble averaging of complex networks of proteins that exhibit varying degrees of structural heterogeneity. Here, we used infrared vibrational scattering-scanning near-field optical microscopy (IR s-SNOM), which provides nanometer spatially resolved chemical spectroscopy, to image protein-protein interactions and conformational heterogeneity of (i) a two-dimensional lipid-like peptoid membrane, and (ii) a three-dimensional catalase tetramer crystal. In the peptoid membrane sample which consists of stacked ~ 4 nm high peptoid monolayers, spatio-spectral linewidth analyses reveal heterogeneity of the vibrational dynamics due to protein-protein or protein-substrate interactions. In s-SNOM imaging of catalase crystals, our results revealed complex secondary structures that vary over nanometer length scales. Broadening of vibrational resonances as observed from the catalase crystals, indicates a higher degree of heterogeneity as compared to the synthetic peptoid membranes. Our results thus demonstrate the utility of IR nanoscopy for the investigation of structural heterogeneity within biological systems with high spatio-spectral resolution and sensitivity.