THE REFINED 3-DIMENSIONAL STRUCTURE OF PECTATE LYASE-C FROM ERWINIA-CHRYSANTHEMI AT 2.2-ANGSTROM RESOLUTION - IMPLICATIONS FOR AN ENZYMATICMECHANISM

The crystal structure of pectate lyase C (EC 4.2.2.2) from the enterob acterium Erwinia chrysanthemi (PelC) has been refined by molecular dyn amics techniques to a resolution of 2.2 Angstrom to an R factor of 17. 97%. The final model consists of 352 of the total 353 amino acids and 114 solvent molecules. The root-mean-square deviation from ideality is 0.009 Angstrom for bond lengths and 1.768 degrees for bond angles. Th e structure of PelC bound to the lanthanide ion lutetium, used as a ca lcium analog, has also been refined. Lutetium inhibits the enzymatic a ctivity of the protein, and in the PelC-lutetium structure, the ion bi nds in the putative calcium-binding site. Five side-chain atoms form l igands to the lutetium ion. An analysis of the atomic-level model of t he two protein structures reveals possible implications for the enzyma tic mechanism of the enzyme.