A nucleotide insertion between two adjacent methyltransferases in Helicobacter pylori results in a bifunctional DNA methyltransferase.
Helicobacter pylori has a dynamic R-M (restriction-modification) system. It is capable of acquiring new R-M systems from the environment in the form of DNA released from other bacteria or other H. pylori strains. Random mutations in R-M genes can result in non-functional R-M systems or R-M systems with new properties. hpyAVIAM and hpyAVIBM are two solitary DNA MTase (methyltransferase) genes adjacent to each other and lacking a cognate restriction enzyme gene in H. pylori strain 26695. Interestingly, in an Indian strain D27, hpyAVIAM-hpyAVIBM encodes a single bifunctional polypeptide due to insertion of a nucleotide just before the stop codon of hpyAVIBM and, when a similar mutation was made in hpyAVIAM-hpyAVIBM from strain 26695, a functional MTase with an N-terminal C⁵-cytosine MTase domain and a C-terminal N⁶-adenine MTase domain was constructed. Mutations in the AdoMet (S-adenosylmethionine)-binding motif or in the catalytic motif of M.HpyAVIA or M.HpyAVIB selectively abrogated the C⁵-cytosine or N⁶-adenine methylation activity of M.HpyAVIA-M.HpyAVIB fusion protein. The present study highlights the ability of H. pylori to evolve genes with unique functions and thus generate variability. For organisms such as H. pylori, which have a small genome, these adaptations could be important for their survival in the hostile host environment.
Department of Biochemistry, Indian Institute of Science, Bangalore, India. rithesh@biochem.iisc.ernet.in
Ritesh
R
Kumar
Desirazu N
DN
Rao
D001665:Binding Sites / Q000235:genetics; D005075:Biological Evolution; D015254:DNA Modification Methylases / Q000235:genetics*; D004262:DNA Restriction Enzymes; D014644:Genetic Variation; D016680:Genome, Bacterial; D016480:Helicobacter pylori / Q000201:enzymology* / Q000235:genetics*; D016254:Mutagenesis, Insertional; D012436:S-Adenosylmethionine / Q000378:metabolism
D012436:S-Adenosylmethionine; D015254:DNA Modification Methylases; D004262:DNA Restriction Enzymes