4.2.2.B7 | wild-type and mutant H531A, in complex with alginate trisaccharide, to 2.1 A and 2.99 A resolution, respectively. Residues H311 and Y365 act as the catalytic base and acid, respectively. A short alpha-helix in the central alpha/alpha-barrel domain and a conformational change at the interface between the central and C-terminal domains are essential for the exolytic mode of action |