Assessing Local Environments in Green Fluorescent Protein using Unnatural Amino Acid 4‐Cyano‐L‐Phenylalanine

Abstract

An increasingly useful method of studying local electrostatic environments within protein molecules is through the incorporation of unnatural amino acids (UAAs) containing distinguishable chemical bonds with specific features in the infrared spectrum (IR) that change based on local environments. Of the existing UAAs, 4-cyano-L-phenylalanine (pCNF) is arguably one of the most useful vibrational reporters due to the fact that it is easily and affordably synthesized, it is well-studied, and its nitrile stretch appears in a biologically quiet region of the IR spectrum. In this study, pCNF has been genetically incorporated individually into three distinct sites of superfolder green fluorescent protein (sfGFP) via the amber codon suppression methodology. According to the wild type crystal structure of sfGFP, each of the selected sites are expected to have a unique solvation environment. Temperature-dependent infrared (IR) spectroscopy was utilized in order to test assess the local solvation environments of each of these sites. By measuring the nitrile stretching frequency as a function of temperature, the degree to which the incorporated pCNF participates in hydrogen bonding was determined. IR data and X-ray crystal structures from these constructs will be presented.