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Vol 44(2010) N 5 p. 807-816; A.Y. Ryazanova1, N.V. Molochkov2, L.A. Abrosimova1, A.V. Alexeevsky1,3, A.S. Karyagina1,4, A.S. Protsenko5, P. Friedhoff6, T.S. Oretskaya1, Е.А.Кубарева1* Secondary Structure of SsoII-like (Cytosine-5)-DNA MethyltransferasesN-Terminal Region Determined by Circular Dichroism Spectroscopy 1Faculty of Bioengineering and Bioinformatics, Chemistry Department, and A.N. Belozersky Institute of Physico-Chemical Biology, M.V. Lomonosov Moscow State University, Moscow, 119991, Russia2Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences, Moscow region Pushchino, 142290, Russia 3Scientific Research Institute for System Studies, Russian Academy of Sciences, Moscow, 117218, Russia 4N.F. Gamaleya Institute of Epidemiology and Microbiology, Russian Academy of Medical Sciences, Moscow, 123098, Russia 5G.K. Skryabin Institute of Biochemistry and Physiology of Microorganisms, Russian Academy of Sciences, Moscow region Pushchino, 142290, Russia 6Institut für Biochemie, Justus-Liebig-Universität, D-35392, Giessen, Germany *kubareva@belozersky.msu.ru Received - 2010-01-28; Accepted - 2010-03-16 (Cytosine-5)-DNA methyltransferase SsoII (M.SsoII) has a long N-terminal region (1-71 residues) preceding the sequence with conservative motifs, which are characteristic for all DNA methyltransferases of such kind. The presence of this region provides M.SsoII capability to act as a transcription regulator in SsoII restriction-modification system. To perform its regulatory function, M.SsoII binds specifically to a 15-mer inverted repeat in the promoter region of SsoII restriction-modification system genes. In the present work, properties of the protein (72-379)M.Ecl18kI are studied, which is a deletion mutant of the SsoII-like DNA-methyltransferase M.Ecl18kI and is homologous to M.SsoII N-terminal region. (72-379)M.Ecl18kI capability to bind specifically a DNA duplex containing the regulatory site is demonstrated. However, such a binding takes place only in the presence of high protein excess relative to DNA, which could indicate an altered structure in the deletion mutant in comparison with the full-length M.SsoII. Circular dichroism spectroscopy demonstrated that (72-379)M.Ecl18kI has a strongly pronounced secondary structure and contains 32% -helices and 20% -strands. Amino acid sequences alignment of M.SsoII N-terminal region and transcription factors of known spatial structure is made. An assumption is made how -helices and -strands are arranged in M.SsoII N-terminal region. DNA methyltransferase, transcription factor, deletion mutant, DNA-protein interactions, protein secondary structure, circular dichroism |
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