Energetics of Ionizable Groups Buried in Proteins

Johns Hopkins University, Baltimore MD

Investigators

Abstract

Lattman MCB 9982967 The objectives of this research are to carry out structural, calorimetric, and stability studies on mutants of staphylococcal nuclease and other proteins in which ionizable sidechains have been buried deep in the protein's hydrophobic core. Earlier measurements have suggested that polarity in the core is much higher than had been previously believed. This project will probe the role of water molecules and other factors as a physical basis for this high polarity and seek to discover whether the observations in nuclease can be generalized to other proteins. In the mutant V66E, studied in collaboration with the laboratory of Bertrand Garcia-Moreno, the X-ray crystal structure shows four water molecules in the structure, connecting the glutamate sidechain with the protein surface. This observation suggests that buried water molecules, ordered or disordered, may play a role in providing the observed polarity. Most biological function comes about through one protein molecule binding to another, or through a small molecule binding to a protein. For example, muscle develops force when actin interacts with myosin, and steroid hormones (non-protein) exert their influence by binding to steroid hormone receptors (proteins). Efforts to create new catalysts (for transforming petroleum products for example) also depend on quantitative understanding of how one molecule binds to another. One of the most important forces involved in stabilizing these interactions is the electrostatic force. This project on implanting charges within proteins should lead to a better understanding of the electrostatic force and so should help improve these methodologies.