Crystal structure of polygalacturonase from Erwinia caratovora ssp. carotovora

Abstract

The crystal structure of the 40-kDa endo-polygalacturonase from Erwinia carotovora ssp. carotovora was solved by multiple isomorphous replacement and refined at 1.9 Å to a conventional crystallographic R-factor of 0.198 and R(free) of 0.239. This is the first structure of a polygalacturonase and comprises a 10 turn right-handed parallel β-helix domain with two loop regions forming a 'tunnel like' substrate-binding cleft. Sequence conservation indicates that the active site of polygalacturonase is between these two loop regions, and comparison of the structure of polygalacturonase with that of rhamnogalacturonase A from Aspergillus aculeatus enables two conserved aspartates, presumed to be catalytic residues, to be identified. An adjacent histidine, in accord with biochemical results, is also seen. A similarity in overall electrostatic properties of the substrate-binding clefts of polygalacturonase and pectate lyase, which bind and cleave the same substrate, polygalacturonic acid, is also revealed.