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Tsunoda T, Abuelizz HA, Samadi A, Wong CP, Awakawa T, Brumsted CJ, Abe I, Mahmud T. Catalytic Mechanism of Nonglycosidic C-N Bond Formation by the Pseudoglycosyltransferase Enzyme VldE. ACS Catal 2023; 13:13369-13382. [PMID: 38130475 PMCID: PMC10732325 DOI: 10.1021/acscatal.3c02404] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2023]
Abstract
The pseudoglycosyltransferase (PsGT) enzyme VldE is a homologue of the retaining glycosyltransferase (GT) trehalose 6-phosphate synthase (OtsA) that catalyzes a coupling reaction between two pseudo-sugar units, GDP-valienol and validamine 7-phosphate, to give a product with α,α-N-pseudo-glycosidic linkage. Despite its biological importance and unique catalytic function, the molecular bases for its substrate specificity and reaction mechanism are still obscure. Here, we report a comparative mechanistic study of VldE and OtsA using various engineered chimeric proteins and point mutants of the enzymes, X-ray crystallography, docking studies, and kinetic isotope effects. We found that the distinct substrate specificities between VldE and OtsA are most likely due to topological differences within the hot spot amino acid regions of their N-terminal domains. We also found that the Asp158 and His182 residues, which are in the active site, play a significant role in the PsGT function of VldE. They do not seem to be directly involved in the catalysis but may be important for substrate recognition or contribute to the overall architecture of the active site pocket. Moreover, results of the kinetic isotope effect experiments suggest that VldE catalyzes a C-N bond formation between GDP-valienol and validamine 7-phosphate via an SNi-like mechanism. The study provides new insights into the substrate specificity and catalytic mechanism of a member of the growing family of PsGT enzymes, which may be used as a basis for developing new PsGTs from GTs.
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Affiliation(s)
- Takeshi Tsunoda
- Department of Pharmaceutical Sciences, Oregon State University, Corvallis, OR 97331-3507, U.S.A
| | - Hatem A. Abuelizz
- Department of Pharmaceutical Sciences, Oregon State University, Corvallis, OR 97331-3507, U.S.A
- Department of Pharmaceutical Chemistry, College of Pharmacy, King Saud University, Riyadh 11451, Saudi Arabia
| | - Arash Samadi
- Department of Pharmaceutical Sciences, Oregon State University, Corvallis, OR 97331-3507, U.S.A
| | - Chin Piow Wong
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Takayoshi Awakawa
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Corey J. Brumsted
- Department of Pharmaceutical Sciences, Oregon State University, Corvallis, OR 97331-3507, U.S.A
| | - Ikuro Abe
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Taifo Mahmud
- Department of Pharmaceutical Sciences, Oregon State University, Corvallis, OR 97331-3507, U.S.A
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