2024-03-29T09:18:11Z
https://niigata-u.repo.nii.ac.jp/oai
oai:niigata-u.repo.nii.ac.jp:00001560
2022-12-15T03:34:14Z
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Site-directed mutagenesis experiments on the putative deprotonation site of squalene-hopene cyclase from Alicyclobacillus acidocaldarius.
Sato, Tsutomu
4300
Kouda, Masanori
4301
Hoshino, Tsutomu
4302
squalene
terpene cyclase
triterpene
To provide insight into the catalytic mechanism for the final deprotonation reaction of squalene-hopene cyclase (SHC) from Alicyclobacillus acidocaldarius, mutagenesis experiments were conducted for the following ten residues: Thr41, Glu45, Glu93, Arg127, Trp133, Gln262, Pro263, Tyr267, Phe434 and Phe437. An X-ray analysis of SHC has revealed that two types of water molecules ("front water" and "back waters") were involved around the deprotonation site. The results of these mutagenesis experiments allow us to propose the functions of these residues. The two residues of Gln262 and Pro263 probably work to keep away the isopropyl group of the hopanyl cation intermediate from the "front water molecule," that is, to place the "front water" in a favorable position, leading to the minimal production of by-products, i.e., hopanol and hop-21(22)-ene. The five residues of Thr41, Glu45, Glu93, Arg127 and Trp133, by which the hydrogen-bonded network incorporating the "back waters" is constructed, increase the polarization of the "front water" to facilitate proton elimination from the isopropyl moiety of the hopanyl cation, leading to the normal product, hop-22(29)-ene. The three aromatic residues of Tyr267, Phe434 and Phe437 are likely to play an important role in guiding squalene from the enzyme surface to the reaction cavity (substrate channeling) by the strong affinity of their aromatic residues to the squalene substrate.
journal article
Japan Society for Bioscience, Biotechnology, and Agrochemistry
2004
application/pdf
Bioscience, Biotechnology, and Biochemistry
3
68
728
738
AA10824164
0916-8451
https://niigata-u.repo.nii.ac.jp/record/1560/files/07_0014.pdf
eng
http://doi.org/10.1271/bbb.68.728