CRYSTAL-STRUCTURE OF POLYGALACTURONASE FROM ERWINIA-CAROTOVORA SSP. CAROTOVORA

The crystal structure of the 40-kDa endo-polygalacturonase from Erwini a carotovora ssp, carotovora was solved by multiple isomorphous replac ement and refined at 1.9 Angstrom to a conventional crystallographic R -factor of .198 and R-free of 0.239, This is the first structure of a polygalacturonase and comprises a 10 turn right-handed parallel beta-h elix 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 o f the structure of polygalacturonase with that of rhamnogalacturonase A from Aspergillus aculeatus enables two conserved aspartates, presume d to be catalytic residues, to be identified. An adjacent histidine, i n accord with biochemical results, is also seen. A similarity in overa ll electrostatic properties of the substrate-binding clefts of polygal acturonase and pectate lyase, which bind and cleave the same substrate , polygalacturonic acid, is also revealed.