CRYSTAL STRUCTURE OF
POLYGALACTURONASE FROM
Erwinia carotovora ssp. carotovora
Richard Pickersgill, Drummond Smith, Kathryn Worboys & John Jenkins
Institute of Food Research, Reading Laboratory, Earley
Gate, Whiteknights Road, Reading RG6 6BZ, UK
E-mail: richard.pickersgill@bbsrc.ac.uk
We have solved the structure of the 40kDa endo-polygalacturonase from Erwinia carotovora ssp. carotovora by multiple isomorphous replacement. The structure has been refined to a conventional crystallographic R-factor of 0.198 and R-free of 0.239 at 1.9 A resolution and comprises a 10 turn right-handed parallel (-helix domain with two loop regions forming a ‘tunnel like’ substrate binding cleft (1). Sequence conservation within the polygalacturonases indicates that the active site is between these two loop regions. Comparison of the structure of polygalacturonase with that of rhamnogalacturonase A from Aspergillus aculeatus (2) 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 (3,4) which bind and cleave the same substrate, polygalacturonic acid, is also revealed. The characteristics of the binding cleft of polygalacturonase is distinct from that of the pectin lyases (5,6).