Geosmin biosynthesis in Streptomyces avermitilis. Molecular cloning, expression, and mechanistic study of the germacradienol/geosmin synthase.
Geosmin (1) is responsible for the characteristic odor of moist soil. The Gram-positive soil bacterium Streptomyces avermitilis produces geosmin (1) as well as its precursor germacradienol (3). The S. avermitilis gene SAV2163 (geoA) is extremely similar to the S. coelicolor A3(2) SCO6073 gene that encodes a germacradienol/geosmin synthase. S. avermitilis mutants with a deleted geoA were unable to produce either germacradienol (3) or geosmin (1). Biosynthesis of both compounds was restored by introducing an intact geoA gene into the mutants. Incubation of recombinant GeoA, encoded by the SAV2163 gene of S. avermitilis, with farnesyl diphosphate (2) in the presence of Mg2+ gave a mixture of (4S,7R)-germacra-1(10)E,5E-diene-11-ol (3) (66%), (7S)-germacrene D (4) (24%), geosmin (1) (8%), and a hydrocarbon, tentatively assigned the structure of octalin 5 (2%). Incubation of this germacradienol/geosmin synthase with [1,1-(2)H2] FPP (2a) gave geosmin-d1 (1a), as predicted. When recombinant GeoA from either S. avermitilis or S. coelicolor A3(2) was incubated with nerolidyl diphosphate (8), only the acyclic elimination products beta3-farnesene (10), (Z)-alpha-farnesene (11), and (E)-alpha-farnesene (12) were formed, thereby ruling out nerolidyl diphosphate as an intermediate in the conversion of farnesyl diphosphate to geosmin, germacradienol, and germacrene D.
Cane
David E
DE
Department of Chemistry, Brown University, Box H, Providence, Rhode Island 02912-9108, USA. David_Cane@brown.edu
He
Xiaofei
X
Kobayashi
Seiji
S
Omura
Satoshi
S
Ikeda
Haruo
H
D003001:Cloning, Molecular; D015964:Gene Expression Regulation, Bacterial; D009284:Naphthols / Q000378:metabolism*; D011106:Polyisoprenyl Phosphates / Q000737:chemistry / Q000378:metabolism; D012717:Sesquiterpenes; D012987:Soil; D013302:Streptomyces / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism
D009284:Naphthols; D011106:Polyisoprenyl Phosphates; D012717:Sesquiterpenes; D012987:Soil; C515287:germacradienol; C004808:farnesyl pyrophosphate; C001278:geosmin