4la5
From Proteopedia
Crystal structure of 2-methylisoborneol synthase from Streptomyces coelicolor A3(2)
Structural highlights
FunctionMIBS_STRCO Catalyzes the cyclization of 2-methylgeranyl diphosphate (2-MeGPP) to 2-methylisoborneol (2-MIB), which likely involves the intermediacy of 2-methyllinalyl diphosphate. Is also able to catalyze the cyclization of geranyl diphosphate (GPP), albeit with much lower efficiency, leading to the formation of a complex mixture of cyclic monoterpenes, consisting of alpha-pinene (6%), beta-pinene (23%), limonene (32%), gamma-terpinene (29%), and delta-terpinene (10%). Publication Abstract from PubMedThe crystal structure of 2-methylisoborneol synthase (MIBS) from Streptomyces coelicolor A3(2) has been determined in its unliganded state and in complex with two Mg2+ ions and 2-fluoroneryl diphosphate at 1.85 and 2.00 A resolution, respectively. Under normal circumstances, MIBS catalyzes the cyclization of the naturally occurring, noncanonical 11-carbon isoprenoid substrate, 2-methylgeranyl diphosphate, which first undergoes an ionization-isomerization-ionization sequence through the tertiary diphosphate intermediate 2-methyllinalyl diphosphate to enable subsequent cyclization chemistry. MIBS does not exhibit catalytic activity with 2-fluorogeranyl diphosphate, and we recently reported the crystal structure of MIBS complexed with this unreactive substrate analogue [ Koksal, M., Chou, W. K. W., Cane, D. E., Christianson, D. W. (2012) Biochemistry 51 , 3011-3020 ]. However, cocrystallization of MIBS with the fluorinated analogue of the tertiary allylic diphosphate intermediate, 2-fluorolinalyl diphosphate, reveals unexpected reactivity for the intermediate analogue and yields the crystal structure of the complex with the primary allylic diphosphate, 2-fluoroneryl diphosphate. Comparison with the structure of the unliganded enzyme reveals that the crystalline enzyme active site remains partially open, presumably due to the binding of only two Mg2+ ions. Assays in solution indicate that MIBS catalyzes the generation of (1R)-(+)-camphor from the substrate 2-fluorolinalyl diphosphate, suggesting that both 2-fluorolinalyl diphosphate and 2-methyllinalyl diphosphate follow the identical cyclization mechanism leading to 2-substituted isoborneol products; however, the initially generated 2-fluoroisoborneol cyclization product is unstable and undergoes elimination of hydrogen fluoride to yield (1R)-(+)-camphor. Unexpected Reactivity of 2-Fluorolinalyl Diphosphate in the Active Site of Crystalline 2-Methylisoborneol Synthase.,Koksal M, Chou WK, Cane DE, Christianson DW Biochemistry. 2013 Jul 22. PMID:23844678[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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