Crystallization of xylanase from Erwinia chrysanthemi: influence of heat and polymeric substrate

Xylanase from the bacterial plant pathogen Erwinia chrysanthemi (E.C. 3.2.1.8), expressed in E. coli, has been crystallized for X-ray diffraction analysis both in the presence and the absence of its polymeric substrate 4-O-methyl glucuronoxylan. In all cases it was found that the quality, time of appearance, and reproducibility of both the native and complex crystals were significantly enhanced by heating of the protein to 323 K prior to dispensing the crystallization trials. Crystals of the native protein are ideal for X-ray diffraction analysis, producing Bragg reflections beyond 1.5 A resolution with virtually no degradation with time. The native crystals are in space group P2(1), with a = 39.33, b = 49.46, c = 90.85 A and beta = 101.58 degrees. Other polymorphs have also been obtained and their cell parameters determined. Crystallization of the enzyme in the presence of polymeric substrate yields two distinctly different crystals at different concentrations of the xylan. These are thought to be complexes of the protein with stable products of the enzymatic reaction. A similar result had been obtained previously with pancreatic alpha-amylase and its substrate glycogen.