1ydx
From Proteopedia
Crystal structure of Type-I restriction-modification system S subunit from M. genitalium
Structural highlights
FunctionT1SX_MYCGE The M and S subunits together form a methyltransferase (MTase) that methylates two adenine residues in complementary strands of a bipartite DNA recognition sequence. 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 PubMedThe crystal structure of the eubacteria Mycoplasma genitalium ORF MG438 polypeptide, determined by multiple anomalous dispersion and refined at 2.3 A resolution, reveals the organization of S subunits from the Type I restriction and modification system. The structure consists of two globular domains, with about 150 residues each, separated by a pair of 40 residue long antiparallel alpha-helices. The globular domains correspond to the variable target recognition domains (TRDs), as previously defined for S subunits on sequence analysis, while the two helices correspond to the central (CR1) and C-terminal (CR2) conserved regions, respectively. The structure of the MG438 subunit presents an overall cyclic topology with an intramolecular 2-fold axis that superimposes the N and the C-half parts, each half containing a globular domain and a conserved helix. TRDs are found to be structurally related with the small domain of the Type II N6-adenine DNA MTase TaqI. These relationships together with the structural peculiarities of MG438, in particular the presence of the intramolecular quasi-symmetry, allow the proposal of a model for S subunits recognition of their DNA targets in agreement with previous experimental results. In the crystal, two subunits of MG438 related by a crystallographic 2-fold axis present a large contact area mainly involving the symmetric interactions of a cluster of exposed hydrophobic residues. Comparison with the recently reported structure of an S subunit from the archaea Methanococcus jannaschii highlights the structural features preserved despite a sequence identity below 20%, but also reveals important differences in the globular domains and in their disposition with respect to the conserved regions. Crystal structure of a putative type I restriction-modification S subunit from Mycoplasma genitalium.,Calisto BM, Pich OQ, Pinol J, Fita I, Querol E, Carpena X J Mol Biol. 2005 Aug 26;351(4):749-62. PMID:16038930[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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