Circular dichroism of the parallel beta helical proteins pectate lyase C and E

The pectate lyases, PelC and PelE, have an unusual folding motif, known as a parallel beta-helix, in which the polypeptide chain is coiled into a larger helix composed of three parallel beta-sheets connected by loops having variable lengths and conformations. Since the regular secondary structure consists almost entirely of parallel beta-sheets these proteins provide a unique opportunity to study the effect of parallel beta-helical structure on circular dichroism (CD). We report here the CD spectra of PelC and PelE in the presence and absence of Ca2+, derive the parallel beta-helical components of the spectra, and compare these results with previous CD studies of parallel beta-sheet structure. The shape and intensity of the parallel beta-sheet spectrum is distinctive and may be useful in identifying other proteins that contain the parallel beta-helical folding motif.