'''Crystal structure of Type-I restriction-modification system S subunit from M. genitalium'''
===Crystal structure of Type-I restriction-modification system S subunit from M. genitalium===
==Overview==
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The 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.
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==About this Structure==
==About this Structure==
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[[Category: Quijada, O.]]
[[Category: Quijada, O.]]
[[Category: Type-i hsd]]
[[Category: Type-i hsd]]
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Revision as of 13:13, 27 July 2008
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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
