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Structural characterization of a modification subunit of a putative type I restriction enzyme from Vibrio vulnificus

Suk-Youl Park1, Hyun-Ju Lee, Jung-Mi Song

  • 1Department of Chemistry, Chonnam National University, Gwangju 500-757, Republic of Korea.

Acta Crystallographica. Section D, Biological Crystallography
|October 24, 2012
PubMed

Insights

Researchers elucidated the crystal structure of a Vibrio vulnificus methyltransferase (vvHsdM) subunit. This structure reveals conserved motifs crucial for binding S-adenosyl-L-methionine (SAM) and methylating DNA.

Area of Science:

  • Biochemistry
  • Structural Biology
  • Enzymology

Background:

  • Type I restriction enzymes are multifunctional proteins essential for DNA modification.
  • Active methyltransferases (MTases) comprise methylation (HsdM) and specificity (HsdS) subunits.
  • Understanding HsdM structure is key to deciphering DNA methylation mechanisms.

Purpose of the Study:

  • To determine the crystal structure of the putative HsdM subunit from Vibrio vulnificus YJ016 (vvHsdM).
  • To identify conserved residues and motifs involved in cofactor binding and substrate recognition.
  • To provide insights into the mechanism of DNA methylation by HsdM subunits.

Main Methods:

  • X-ray crystallography was used to elucidate the 3D structure of vvHsdM at 1.80 Å resolution.
  • Bioinformatic comparisons were made with other known HsdM and N6 DNA MTase structures.
  • Analysis of conserved motifs and residue interactions within the cofactor-binding site.

Main Results:

  • The crystal structure of vvHsdM revealed an α/β-fold with a C-terminal cofactor-binding site for S-adenosyl-L-methionine (SAM).
  • Conserved residues, including GxGG and (N/D)PP(F/Y) motifs, were identified and implicated in SAM binding.
  • Structural comparisons suggest that conserved aromatic residues (Phe199, Phe312) may interact with the adenine ring of DNA, positioning it for methylation by a conserved Asn residue (Asn309).

Conclusions:

  • The elucidated vvHsdM structure provides a detailed molecular basis for SAM binding and methyltransferase activity.
  • Conserved structural features are critical for the precise positioning of the DNA target base and the methyl donor.
  • This study enhances our understanding of the catalytic mechanism of type I restriction enzyme methyltransferase subunits.

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