The Three-Dimensional Structure of Pectate Lyase E, a Plant Virulence Factor from Erwinia chrysanthemi

The three-dimensional structure of pectate lyase E (PelE) has been determined by crystallographic techniques at a resolution of 2.2 A. The model includes all 355 amino acids but no solvent, and refines to a crystallographic refinement factor of 20.6%. The polypeptide backbone folds into a large right-handed cylinder, termed a parallel [beta] helix. Loops of various sizes and conformations protrude from the central helix and probably confer function. A putative Ca2+-binding site as well as two cationic sites have been deduced from the location of heavy atom derivatives. Comparison of the PelE and recently determined pectate lyase C (PelC) structures has led to identification of a putative polygalacturonate-binding region in PelE. Structural differences relevant to differences in the enzymatic mechanism and maceration properties of PelE and PelC have been identified. The comparative analysis also reveals a large degree of structural conservation of surface loops in one region as well as an apparent aromatic specificity pocket in the amino-terminal branch. Also discussed is the sequence and possible functional relationship of the pectate lyases with pollen and style plant proteins.