Abstract
Alginate lyases depolymerize alginate, a heteropolysaccharide consisting of alpha-L-guluronate and beta-D-mannuronate, through a beta-elimination reaction. The alginate lyases A1-II (25 kDa) and A1-II' (25 kDa) from Sphingomonas sp. A1, which belong to polysaccharide lyase family PL-7, exhibit 68% homology in primary structure but have different substrate specificities. To determine clearly the structural basis for substrate recognition in the depolymerization mechanism by alginate lyases, both proteins were crystallized at 293 K using the vapour-diffusion method. A crystal of A1-II belonged to space group P2(1) and diffracted to 2.2 A resolution, with unit-cell parameters a = 51.3, b = 30.1, c = 101.6 A, beta = 100.2 degrees, while a crystal of A1-II' belonged to space group P2(1)2(1)2(1) and diffracted to 1.0 A resolution, with unit-cell parameters a = 34.6, b = 68.5, c = 80.3 A.