Protein Folding Triggered by Electron Transfer

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9630465 Winkler The basic requirement for experimental investigations of protein-folding kinetics is some means of triggering the folding (or unfolding) process. In this research program, a new triggering method that permits measurements in the nanosecond-to-millisecond time range will be employed. Electron-transfer (ET) chemistry can trigger folding reactions in many proteins, and there are many well established techniques for rapidly injecting electrons into proteins on timescales as short as a few nanoseconds. Specifically, laser-initiated ET will be used to trigger the folding of three high-potential heme proteins; cytochrome c, cytochrome b562 and cytochrome f. The complex process of protein folding involves dynamics that span more than twelve orders of magnitude in time (picoseconds to minutes). The power of ET-initiated protein folding is that it lays open this entire time regime for direct examination; when coupled with the techniques of protein engineering, it will permit evaluation of the importance of individual amino acids in each step of the folding process. %%% Proteins are heteropolymers (polypeptides) built from the twenty naturally occurring amino acids, often in combination with one or more cofactors. The three-dimensional structure - the fold - of a protein that defines its biological activity is determined by the sequence of amino acids in the polypeptide chain. The ultimate objective in proteinfolding research then, is the ability to predict the three dimensional structure of a protein solely on the basis of its amino-acid sequence. An essential key to the problem is understanding the series of chemical events that transforms a randomly configured polypeptide into a fully folded protein. There are many methods available for studying protein-folding kinetics but, for the most part, they are limited to measurement timescales longer than one millisecond. There is compelling evidence, however, that in many proteins a substantial degre e of secondary and tertiary protein structure can develop on faster timescales. Therefore, new experimental methods are required to observe the earliest events in protein folding. ***