Conformational and aggregational properties of the gene 9 minor coat protein of bacteriophage M13 in membrane-mimicking systems

The membrane-bound state of the gene 9 minor coat protein of bacteriophage M13 was studied in various membrane-mimicking systems, including organic so lvents, detergent micelles, and phospholipid bilayers. For this purpose we determined the conformational and aggregational properties of the chemicall y synthesized protein by CD, FTIR, and HPSEC. The protein appears to be in a monomeric or small oligomeric alpha-helical state in TFE but adopts a mix ture of alpha-helical and random structure after subsequent incorporation i nto SDS or DOPG. When solubilized by sodium cholate, however, the protein u ndergoes a transition in time into large aggregates, which contain mainly b eta-sheet conformation. The rate of this beta-polymerization process was de creased at lower temperature and higher concentrations of sodium cholate. T his aggregation was reversed only upon addition of high concentrations of t he strong detergent SDS. By reconstitution of the cholate-solubilized prote in into DOPG, it was found that the state of the protein, whether initially alpha-helical monomeric/oligomeric or beta-sheet aggregate, did not change . On the basis of our results, we propose that the principal conformational state of membrane-bound gene 9 protein in vive is alpha-helical.