Structural highlights
Function
[T1S1_METJA] The M and S subunits together form a methyltransferase (MTase) that methylates two adenine residues in complementary strands of a bipartite DNA recognition sequence. In the presence of the R subunit the complex can also act as an endonuclease, binding to the same target sequence but cutting the DNA some distance from this site. Whether the DNA is cut or modified depends on the methylation state of the target sequence. When the target site is unmodified, the DNA is cut. When the target site is hemimethylated, the complex acts as a maintenance MTase modifying the DNA so that both strands become methylated. Subunit S dictates DNA sequences specificity (By similarity).
Evolutionary Conservation
Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf.
Publication Abstract from PubMed
Type I restriction-modification enzymes are differentiated from type II and type III enzymes by their recognition of two specific dsDNA sequences separated by a given spacer and cleaving DNA randomly away from the recognition sites. They are oligomeric proteins formed by three subunits: a specificity subunit, a methylation subunit, and a restriction subunit. We solved the crystal structure of a specificity subunit from Methanococcus jannaschii at 2.4-A resolution. Two highly conserved regions (CRs) in the middle and at the C terminus form a coiled-coil of long antiparallel alpha-helices. Two target recognition domains form globular structures with almost identical topologies and two separate DNA binding clefts with a modeled DNA helix axis positioned across the CR helices. The structure suggests that the coiled-coil CRs act as a molecular ruler for the separation between two recognized DNA sequences. Furthermore, the relative orientation of the two DNA binding clefts suggests kinking of bound dsDNA and exposing of target adenines from the recognized DNA sequences.
Crystal structure of DNA sequence specificity subunit of a type I restriction-modification enzyme and its functional implications.,Kim JS, DeGiovanni A, Jancarik J, Adams PD, Yokota H, Kim R, Kim SH Proc Natl Acad Sci U S A. 2005 Mar 1;102(9):3248-53. Epub 2005 Feb 22. PMID:15728358[1]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Kim JS, DeGiovanni A, Jancarik J, Adams PD, Yokota H, Kim R, Kim SH. Crystal structure of DNA sequence specificity subunit of a type I restriction-modification enzyme and its functional implications. Proc Natl Acad Sci U S A. 2005 Mar 1;102(9):3248-53. Epub 2005 Feb 22. PMID:15728358
