NEW DOMAIN MOTIF - THE STRUCTURE OF PECTATE LYASE-C, A SECRETED PLANTVIRULENCE FACTOR

Pectate lyases are secreted by pathogens and initiate soft-rot disease s in plants by cleaving polygalacturonate, a major component of the pl ant cell wall. The three-dimensional structure of pectate lyase C from Erwinia chrysanthemi has been solved and refined to a resolution of 2 .2 angstroms. The enzyme folds into a unique motif of parallel beta st rands coiled into a large helix. Within the core, the amino acids form linear stacks and include a novel asparagine ladder. The sequence sim ilarities that pectate lyases share with pectin lyases, pollen and sty le proteins, and tubulins suggest that the parallel beta helix motif m ay occur in a broad spectrum of proteins.