CONFORMATIONAL CHANGES DURING REVERSIBLE DEPOLYMERIZATION OF PROTEIN COAT FROM BACTERIOPHAGE FR

By measuring the circular dichroism, changes occurring in the secondary structure of the protein subunit of the icosahedral bacteriophage fr during reversible depolymerization of the protein coat with acetic acid were investigated. The measurements were performed in the peptide bond absorption range from 190 to 240 mμ. The results demonstrate that reversible depolymerization is coupled with a reversible denaturation, occurring in several stages. The native conformation of the protein subunit is replaced by a more helical one when the protein coat is split with 11 M acetic acid. Removing the acetic acid by dialysis against water results in a breakdown of the newly-formed structure and the formation of a random coil. At an acetic acid concentration below 0.3 M, the peptide chain begins to refold into the native conformation; this refolding only is dependent on the pH (pK 2.8) and probably is induced by the ionization of the C-terminal carboxyl group. © 1969.