The pectate lyase (Bsp165PelA) from Bacillus sp. N16-5 has great potential in industrial applications because it shows high specific activity under extremely alkaline conditions. Besides, activity measurement of Bsp165PelA does not require addition of calcium, in a way different from the other pectate lyases. Here we report crystal structures of Bsp165PelA in apo-form and in complex with trigalacturonate. The parallel beta-helix, active site residues and substrate binding cleft are similar to those in the other pectate lyases from Polysaccharide Lyase family 1. However, some of the highly conserved Ca2+ binding residues and secondary structures are altered in Bsp165PelA, making it difficult to coordinate with Ca2+ as in the other pectate lyases. We found Bsp165PelA forms some direct enzyme-substrate interactions instead of using Ca2+ ions bridging in the extremely alkaline environment. (C) 2012 Elsevier Inc. All rights reserved.