Secondary structure of SsoII-like (Cytosine-5)-DNA methyltransferases N-terminal region determined by Circular dichroism spectroscopy

• Published in: Molecular biology (New York) Vol. 44; no. 5; pp. 807 - 816
• Main Authors: Ryazanova, A. Yu, Molochkov, N. V, Abrosimova, L. A, Alexeevsky, A. V, Karyagina, A. S, Protsenko, A. S, Friedhoff, P, Oretskaya, T. S, Kubareva, E. A
• Format: Journal Article
• Language: English
• Published: Dordrecht Dordrecht : SP MAIK Nauka/Interperiodica 01.10.2010; SP MAIK Nauka/Interperiodica; Springer Nature B.V
• Subjects: Binding sites; Biochemistry; Biomedical and Life Sciences; Deoxyribonucleic acid; DNA; Genetics; Human Genetics; Life Sciences; Mutation; Spectrum analysis; Structural-Functional Analysis of Biopolymers and Their Complexes; DNA-protein interactions; transcription factor; protein secondary structure; DNA methyltransferase; deletion mutant; circular dichroism
• ISSN: 0026-8933; 1608-3245
• DOI: 10.1134/S0026893310050183

(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 methyltrans-ferases 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 Δ(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. Δ(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 Δ(72-379)M.Ecl18kI has a strongly pronounced secondary structure and contains 32% α-helices and 20% β-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 α-helices and β-strands are arranged in M.SsoII N-terminal region.