Crystallization and preliminary X-ray analysis of β-glucan exohydrolase isoenzyme ExoI from barley (Hordeum vulgare)

Crystals of a β-glucan exohydrolase purified from extracts of young barley seedlings have been obtained by vapour diffusion in the presence of ammonium sulfate and polyethylene glycol. The enzyme exhibits broad substrate specificity against (1,3)-, (1,3;1,4)- and (1,3;1,6)-β-glucans, and related oligosaccharides. Crystal dimensions of up to 0.8 × 0.4 × 0.6 mm have been observed. The crystals belong to the tetragonal space group P4₁2₁2 or P4₃2₁2. Cell parameters are a = b = 102.1 and c = 184.5 Å, and there appear to be eight molecules in the asymmetric unit. The crystals diffract to at least 2.2 Å resolution using X-rays from a rotating-anode generator.