Structural analysis of coniferyl alcohol 9-O-methyltransferase from Linum nodiflorum reveals a novel active-site environment.

Coniferyl alcohol 9-O-methyltransferase from Linum nodiflorum (Linaceae) catalyzes the unusual methylation of the side-chain hydroxyl group of coniferyl alcohol. The protein was heterologously expressed in Escherichia coli as a hexahistidine derivative and purified for crystallization. Diffracting crystals were obtained of the pure protein and of its selenomethionine derivative, as well as of complexes with coniferyl alcohol and with S-adenosyl-L-homocysteine together with coniferyl alcohol 9-O-methyl ether (PDB entries 4ems, 4e70 and 4evi, respectively). The X-ray structures show that the phenylpropanoid binding mode differs from other phenylpropanoid O-methyltransferases such as caffeic acid O-methyltransferase. Moreover, the active site lacks the usually conserved and catalytic histidine residue and thus implies a different reaction mode for methylation. Site-directed mutagenesis was carried out to identify critical amino acids. The binding order of coniferyl alcohol and S-adenosyl-L-methionine was investigated by isothermal titration calorimetry experiments.

Bidentate Zinc chelators for alpha-carbonic anhydrases that produce a trigonal bipyramidal coordination geometry.

A series of new zinc binding groups (ZBGs) has been evaluated kinetically on 13 carbonic anhydrase (CA) isoforms. The fragments show affinity for all isoforms with IC(50) values in the range of 2-11 microM. The crystal structure of hCA II in complex with one such fragment reveals a bidentate binding mode with a trigonal-bipyramidal coordination geometry at the Zn(2+) center. The fragment also interacts with Thr199 and Thr200 through hydrogen bonding and participates in a water network. Further development of this ZBG should increase the binding affinity leading to a structurally distinct and promising class of CA inhibitors.