Crystal structure of the promutagen O4-methylthymidine: importance of the anti conformation of the O(4) methoxy group and possible mispairing of O4-methylthymidine with guanine.

Published

Journal Article

O4-Methylthymidine (O4medT) is a promutagen. To correlate its biological properties to changes in the electronic, geometric, and conformational properties of the pyrimidine base resulting from the keto to enol shift arising from methylation, an X-ray study of O4medT was undertaken. The crystal data are a = 4.950 (2) A, b = 12.648 (1) A, c = 19.305 (2) A, space group P2(1)2(1)2(1), Z = 4, and R = 0.042. The D-deoxyribofuranosyl ring is puckered in the uncommon 1T2 twist conformation with the phase angle of pseudorotation P = 133.8 (5)degrees. The amplitude of puckering tau m = 31.4 (3)degrees shows that the ring is considerably flattened. The base is in the anti conformation [chi CN = 40.6 (4)degrees], and the exocyclic C(4')-C(5') bond (psi) is gauche+ [46.2 (5)degrees]. Methylation produces cytosine-like conjugation for the thymine base. The methoxy group takes the syn-periplanar conformation. Two types of mispairings with guanine are possible, and both require the anti conformation for the O(4) methoxy group. Semiempirical energy calculations have been carried out and reveal that the anti conformation can be energetically assumed in the double helix by widening the exocyclic angles C(5)-C(4)-O(4) and C(4)-C(5)-C(7) and the angle C(4)-O(4)-C(8) at the methoxy group. Such coordinated expansion relieves unfavorable interactions between the C(7) and C(8) methyl groups.

Full Text

Duke Authors

Cited Authors

  • Brennan, RG; Pyzalska, D; Blonski, WJ; Hruska, FE; Sundaralingam, M

Published Date

  • March 11, 1986

Published In

Volume / Issue

  • 25 / 5

Start / End Page

  • 1181 - 1185

PubMed ID

  • 3964665

Pubmed Central ID

  • 3964665

International Standard Serial Number (ISSN)

  • 0006-2960

Digital Object Identifier (DOI)

  • 10.1021/bi00353a036

Language

  • eng

Conference Location

  • United States