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- Title
Roles of the hydroxy group of tyrosine in crystal structures of Sulfurisphaera tokodaiiO<sup>6</sup>‐methylguanine‐DNA methyltransferase.
- Authors
Kikuchi, Makiko; Yamauchi, Takahiro; Iizuka, Yasuhito; Tsunoda, Masaru
- Abstract
O6‐Methylguanine‐DNA methyltransferase (MGMT) removes cytotoxic O6‐alkyl adducts on the guanine base and protects the cell from genomic damage induced by alkylating agents. Although there are reports of computational studies on the activity of the enzyme with mutations at tyrosine residues, no studies concerning the crystal structure of its mutants have been found. In this study, the function of Tyr91 was investigated in detail by comparing the crystal structures of mutants and their complexes with substrate analogs. In this study, tyrosine, a conserved amino acid near the active‐site loop in the C‐terminal domain of Sulfurisphaera tokodaii MGMT (StoMGMT), was mutated to phenylalanine to produce a Y91F mutant, and the cysteine which is responsible for receiving the methyl group in the active site was mutated to a serine to produce a C120S mutant. A Y91F/C120S double‐mutant StoMGMT was also created. The function of tyrosine is discussed based on the crystal structure of Y91F mutant StoMGMT. The crystal structures of StoMGMT were determined at resolutions of 1.13–2.60 Å. They showed no structural changes except in the mutated part. No electron density for deoxyguanosine or methyl groups was observed in the structure of Y91F mutant crystals immersed in O6‐methyl‐2′‐deoxyguanosine, nor was the group oxidized in wild‐type StoMGMT. Therefore, the hydroxy group of Tyr91 may prevent the oxidant from entering the active site. This suggests that tyrosine, which is highly conserved at the N‐terminus of the helix–turn–helix motif across species, protects the active site of MGMTs, which are deactivated after repairing only one alkyl adduct. Overall, the results may provide a basis for understanding the molecular mechanisms by which high levels of conserved amino acids play a role in ensuring the integrity of suicide enzymes, in addition to promoting their activity.
- Subjects
CRYSTAL structure; O6-Methylguanine-DNA Methyltransferase; HELIX-loop-helix motifs; PHENYLALANINE; ALKYLATING agents; METHYLGUANINE; TYROSINE
- Publication
Acta Crystallographica: Section F, Structural Biology Communications, 2021, Vol 77, Issue 12, p444
- ISSN
2053-230X
- Publication type
Article
- DOI
10.1107/S2053230X21011055