Department of Biochemistry, Indian Institute of Science, Bangalore, India.
FEBS J. 2010 Apr;277(7):1666-83. doi: 10.1111/j.1742-4658.2010.07593.x. Epub 2010 Feb 17.
Genomic sequences of Helicobacter pylori strains 26695, J99, HPAGI and G27 have revealed an abundance of restriction and modification genes. hp0050, which encodes an N(6) adenine DNA methyltransferase, was cloned, overexpressed and purified to near homogeneity. It recognizes the sequence 5'-GRRG-3' (where R is A or G) and, most intriguingly, methylates both adenines when R is A (5'-GAAG-3'). Kinetic analysis suggests a nonprocessive (repeated-hit) mechanism of methylation in which HP0050 methyltransferase methylates one adenine at a time in the sequence 5'-GAAG-3'. This is the first report of an N(6) adenine DNA methyltransferase that methylates two adjacent residues on the same strand. Interestingly, HP0050 homologs from two clinical strains of H. pylori (PG227 and 128) methylate only 5'-GAGG-3' compared with 5'-GRRG-3' in strain 26695. HP0050 methyltransferase is highly conserved as it is present in more than 90% of H. pylori strains. Inactivation of hp0050 in strain PG227 resulted in poor growth, suggesting its role in the biology of H. pylori. Collectively, these findings provide impetus for exploring the role(s) of this conserved DNA methyltransferase in the cellular processes of H. pylori.
幽门螺旋杆菌 26695 株、J99 株、HPAGI 株和 G27 株的基因组序列揭示了大量的限制和修饰基因。克隆、过表达和纯化了编码 N(6)腺嘌呤 DNA 甲基转移酶的 hp0050，使其接近均一。它识别序列 5'-GRRG-3'（其中 R 是 A 或 G），最有趣的是，当 R 是 A 时，它甲基化两个腺嘌呤（5'-GAAG-3'）。动力学分析表明，HP0050 甲基转移酶的甲基化是一种非连续（重复打击）的机制，其中一次在序列 5'-GAAG-3'中甲基化一个腺嘌呤。这是第一个报道的甲基化同一链上两个相邻残基的 N(6)腺嘌呤 DNA 甲基转移酶。有趣的是，来自两种临床幽门螺旋杆菌株（PG227 和 128）的 HP0050 同源物仅甲基化 5'-GAGG-3'，而 26695 株则甲基化 5'-GRRG-3'。HP0050 甲基转移酶高度保守，因为它存在于超过 90%的幽门螺旋杆菌株中。在 PG227 株中失活 hp0050 导致生长不良，表明其在幽门螺旋杆菌生物学中的作用。总之，这些发现为探索这种保守的 DNA 甲基转移酶在幽门螺旋杆菌细胞过程中的作用提供了动力。
