STRUCTURE OF A METHIONINE-RICH SEGMENT OF ESCHERICHIA-COLI FFH PROTEIN

The methionine-rich segments of the Ffh protein of Escherichia coli an d its eukaryotic counterpart SRP54 are thought to bind signal sequence s of secretory proteins. The structure of a chemically synthesized 25- residue-long peptide corresponding to one of the proposed methionine-r ich amphiphilic helices of Ffh was determined in water and in aqueous trifluroethanol (TFE) solution using CD and NMR. An appreciable alpha- helix conformation exists even in water and this peptide assumes a sta ble alpha-helix along most of its length in aqueous TFE solution, It i s clear that this segment of Ffh protein has a very strong propensity to form alpha-helical structure.