Functional analysis of Gln-237 mutants of HhaI methyltransferase

Nucleic Acids Res. 1995 Feb 25;23(4):620-7. doi: 10.1093/nar/23.4.620.

Abstract

When the HhaI (cytosine-5) methyltransferase (M.HhaI) binds DNA it causes the target cytosine to be flipped 180 degrees out of the helix. The space becomes occupied by two amino acids, Ser-87 and Gln-237, which enter the helix from opposite sides and form a hydrogen bond to each other. Gln-237 may be involved in specific sequence recognition since it forms three hydrogen bonds to the orphan guanosine, which is the partner of the target cytosine. We have prepared all 19 mutants of Gln-237 and tested their biochemical properties. We find that mutations of this residue greatly affect the stability of the M.HhaI-DNA complex without affecting the enzyme's specificity for the target sequence. Surprisingly, all mutants retain detectable levels of enzymatic activity.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Base Sequence
  • Cytosine / chemistry
  • DNA, Bacterial / chemistry
  • DNA, Bacterial / metabolism*
  • DNA-Cytosine Methylases / chemistry
  • DNA-Cytosine Methylases / genetics
  • DNA-Cytosine Methylases / metabolism*
  • Glycine / chemistry
  • Guanosine / chemistry
  • Hydrogen Bonding
  • Models, Molecular*
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Nucleic Acid Conformation*
  • Protein Binding
  • Protein Conformation*
  • Serine / chemistry
  • Substrate Specificity

Substances

  • DNA, Bacterial
  • Guanosine
  • Serine
  • Cytosine
  • DNA modification methylase HhaI
  • DNA-Cytosine Methylases
  • Glycine