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

The pectate lyases, PelC and PelE, have an unusual folding motif, known as a parallel β‐helix, in which the polypeptide chain is coiled into a larger helix composed of three parallel β‐sheets connected by loops having variable lengths and conformations. Since the regular secondary structure consists almost entirely of parallel β‐sheets these proteins provide a unique opportunity to study the effect of parallel β‐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 β‐helical components of the spectra, and compare these results with previous CD studies of parallel β‐sheet structure. The shape and intensity of the parallel β‐sheet spectrum is distinctive and may be useful in identifying other proteins that contain the parallel β‐helical folding motif. © 1995 Wiley‐Liss, Inc.