Solution NMR studies of colicin E1 C-terminal thermolytic peptide. Structural comparison with colicin A and the effects of pH changes

The aqueous solution structure of the C-terminal thermolytic peptide of colicin E1 has been investigated using both one- and two-dimensional NMR techniques. The NMR data are consistent with a fold for the peptide very similar to that reported for the colicin A C-terminal peptide in the crystalline state, although some differences have been noted. The one-dimensional NMR spectrum of the peptide has been used to follow changes in both the structure and dynamics of the peptide on changing pH. The in vitro functionally competent form of the peptide (present in solution only below pH 6) does not differ in structure significantly from the higher pH form. However, small local conformational changes are observed together with an increase in mobility in some of the more hydrophilic regions. This suggests that the effect of lower pH is to change the ease with which the major conformational changes during insertion into a membrane can occur.