Mechanisms of base selection by the Escherichia coli mispaired uracil glycosylase

作者：Liu Pingfang; Theruvathu Jacob A; Darwanto Agus; Lao Victoria Valinluck; Pascal Tod; Goddard William A III; Sowers Lawrence C^*

来源：Journal of Biological Chemistry, 2008, 283(14): 8829-8836.

DOI：10.1074/jbc.M707174200

The repair of the multitude of single-base lesions formed daily in cells of all living organisms is accomplished primarily by the base excision repair pathway that initiates repair through a series of lesion-selective glycosylases. In this article, singleturnover kinetics have been measured on a series of oligonucleotide substrates containing both uracil and purine analogs for the Escherichia coli mispaired uracil glycosylase ( MUG). The relative rates of glycosylase cleavage have been correlated with the free energy of helix formation and with the size and electronic inductive properties of a series of uracil 5-substituents. Data are presented that MUG can exploit the reduced thermodynamic stability of mispairs to distinguish U: A from U: G pairs. Discrimination against the removal of thymine results primarily from the electron-donating property of the thymine 5-methyl substituent, whereas the size of the methyl group relative to a hydrogen atom is a secondary factor. A series of parameters have been obtained that allow prediction of relative MUG cleavage rates that correlate well with observed relative rates that vary over 5 orders of magnitude for the series of base analogs examined. We propose that these parameters may be common among DNA glycosylases; however, specific glycosylases may focus more or less on each of the parameters identified. The presence of a series of glycosylases that focus on different lesion properties, all coexisting within the same cell, would provide a robust and partially redundant repair system necessary for the maintenance of the genome.

• 出版日期2008-4-4