Investigation of solvent accessibility of the fluorotyrosyl residues of M13 coat protein in deoxycholate micelles and phospholipid vesicles.

We have utilized a nonperturbing nuclear magnetic resonance technique, specifically measuring sensitivity of the chemical shift of fluorotyrosyl residues to change in solvent from H2O to D2O, to demonstrate that the tyrosyl residues of fluorotyrosyl M13 coat protein in phospholipid vesicles are not accessible to solvent i.e., are buried in the hydrophobic portion of the bilayer. The two fluorotyrosyl residues of the protein did show partial exposure to solvent (42% and 65% with respect to aqueous m-fluorotyrosine) when the protein was incorporated into deoxycholate micelles, pointing to differences in conformation of micellar protein with respect to vesicle-associated protein. M13 coat protein in phospholipid vesicles was not sensitive to lactoperoxidase-catalyzed iodination, supporting the NMR results. Coat protein in deoxycholate micelles showed release of fluorotyrosyl residues upon Pronase digestion, but only after an observed change in environment. The observed changes suggest that proteolytic digestion studies of membrane proteins should be interpreted with the possibility of artifacts related to conformational changes in mind. M13 coat protein in phospholipid vesicles did not demonstrate release of fluorotyrosine by Pronase, again pointing to differences between protein in micelles and in vesicles and corroborating the NMR result.