The structure of Bacillus subtilis pectate lyase in complex with calcium

We have solved the structure of the Bacillus subtilis pectate lyase (BsPel) in complex with calcium. The structure consists of a parallel β-helix domain and a loop region. The αL-bounded β-strand seen in BsPel is a new element of protein structure and its frequent occurrence suggests it is an important characteristic of the parallel β-helix. A pronounced cleft is formed between the loops and the parallel β-helix domain and we propose that this is the active site cleft. Calcium, essential for the activity of the enzyme, binds at the bottom of this cleft and an arginine residue close to the calcium, which is conserved across all pectin and pectate lyases, may be involved in catalysis.