FUNCTIONAL IMPLICATIONS OF STRUCTURE-BASED SEQUENCE ALIGNMENT OF PROTEINS IN THE EXTRACELLULAR PECTATE LYASE SUPERFAMILY

Pectate lyases are plant Virulence factors that degrade the pectate co mponent of the plant cell wall. The enzymes share considerable sequenc e homology with plant pollen and style proteins, suggesting a shared s tructural topology and possibly functional relationships as well. The three-dimensional structures of two Erwinia chrysanthemi pectate lyase s, C and E, have been superimposed and the structurally conserved amin o acids have been identified. There are 232 amino acids that superimpo se with a root-mean-square deviation of 3 Angstrom or less. These amin o acids have been used to correct the primary sequence alignment deriv ed from evolution-based techniques. Subsequently, multiple alignment t echniques have allowed the realignment of other extracellular pectate lyases as well as all sequence homologs, including pectin lyases and t he plant pollen and style proteins. The new multiple sequence alignmen t reveals amino acids likely to participate in the parallel beta helix motif, those involved in binding Ca2+, and those invariant amino acid s with potential catalytic properties. The latter amino acids cluster in two well-separated regions on the pectate lyase structures, suggest ing two distinct enzymatic functions for extracellular pectate lyases and their sequence homologs.