Protein folding mechanisms

Introduction One of the greatest challenges in modern structural biology is to understand how a newly formed polypeptide sequence finds its correct and unique fold. Real progress has been made towards establishing a fundamental and universal mechanism by which protein folding takes place, and such advances have come from the combination of experimental and theoretical techniques. In our laboratory we are studying the folding of three all α-helical proteins. The four-helix bacterial immunity proteins Im7 and Im9 have been the focus of our studies for 8 years. These proteins are structural homologues with high sequence identity, however they fold with mechanisms of different complexity. Im7 has been shown to fold via a compact, helical, on-pathway intermediate, while under the same conditions Im9 folds directly from the unfolded to the native state. We have shown the folding landscape of these closely homologous proteins to be finely balanced, such that small changes in sequence, or minor alterations in the folding conditions, can switch the kinetic mechanism of folding from twoto three-state. More recently we have extended our studies to include the ultra-fast folding three-helix bundle B domain of staphylococcal protein A (BdpA). We are using an array of biophysical methods to explore the folding landscapes of these three proteins, including laser temperature jump, ultra-rapid mixing, stopped flow and NMR.