title: Structure of geranyl diphosphate C-methyltransferase from Streptomyces coelicolor and implications for the mechanism of isoprenoid modification.
abstract: Geranyl diphosphate C-methyltransferase (GPPMT) from Streptomyces coelicolor A3(2) is the first methyltransferase discovered that modifies an acyclic isoprenoid diphosphate, geranyl diphosphate (GPP), to yield a noncanonical acyclic allylic diphosphate product, 2-methylgeranyl diphosphate, which serves as the substrate for a subsequent cyclization reaction catalyzed by a terpenoid cyclase, methylisoborneol synthase. Here, we report the crystal structures of GPPMT in complex with GPP or the substrate analogue geranyl S-thiolodiphosphate (GSPP) along with S-adenosyl-L-homocysteine in the cofactor binding site, resulting from in situ demethylation of S-adenosyl-L-methionine, at 2.05 or 1.82 Å resolution, respectively. These structures suggest that both GPP and GSPP can undergo catalytic methylation in crystalline GPPMT, followed by dissociation of the isoprenoid product. S-Adenosyl-L-homocysteine remains bound in the active site, however, and does not exchange with a fresh molecule of cofactor S-adenosyl-L-methionine. These structures provide important clues about the molecular mechanism of the reaction, especially with regard to the face of the 2,3 double bond of GPP that is methylated as well as the stabilization of the resulting carbocation intermediate through cation-π interactions.
authors.affiliation: Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania, 231 South 34th Street, Philadelphia, Pennsylvania 19104-6323, USA.
authors.forename: Mustafa
authors.initials: M
authors.lastname: Köksal
authors.forename: Wayne K W
authors.initials: WK
authors.lastname: Chou
authors.forename: David E
authors.initials: DE
authors.lastname: Cane
authors.forename: David W
authors.initials: DW
authors.lastname: Christianson
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D018360:Crystallography, X-Ray; D011756:Diphosphates / Q000737:chemistry* / Q000378:metabolism; D004224:Diterpenes / Q000737:chemistry* / Q000378:metabolism; D008745:Methylation; D008780:Methyltransferases / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D012436:S-Adenosylmethionine / Q000378:metabolism; D048372:Streptomyces coelicolor / Q000201:enzymology* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D011756:Diphosphates; D004224:Diterpenes; C511282:geranyl diphosphate; D012436:S-Adenosylmethionine; D008780:Methyltransferases