We have solved the structure of the Bacillus subtilis pectate lyase (B
sPel) in complex with calcium, The structure consists of a parallel be
ta-helix domain and a loop region. The alpha(L)-bounded beta-strand se
en in BsPel is a new element of protein structure and its frequent occ
urrence suggests it is an important characteristic of the parallel bet
a-helix, A pronounced cleft is formed between the loops and the parall
el beta-helix domain and we propose that this is the active site deft.
Calcium, essential for the activity of the enzyme, binds at the botto
m of this cleft and an arginine residue dose to the calcium, which is
conserved across all pectin and pectate lyases, may be involved in cat
alysis.