title: Structure of the second Single Stranded DNA Binding protein (SSBb) from Mycobacterium smegmatis.
abstract: All mycobacteria with sequenced genomes, except M. leprae, have a second Single Stranded DNA Binding protein (SSBb) in addition to the canonical one (SSBa). This paralogue from M. smegmatis (MsSSBb) has been cloned, expressed and purified. The protein, which is probably involved in stress response, has been crystallized and X-ray analyzed in the first structure elucidation of a mycobacterial SSBb. In spite of the low sequence identity between SSBas and SSBbs in mycobacteria, the tertiary and quaternary structure of the DNA binding domain of MsSSBb is similar to that observed in mycobacterial SSBas. In particular, the quaternary structure is 'clamped' using a C-terminal stretch of the N-domain, which endows the tetrameric molecule with additional stability and its characteristic shape. Comparison involving available, rather limited, structural data on SSBbs from other sources, appears to suggest that SSBbs could exhibit higher structural variability than SSBas do.
authors.affiliation: Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012, Karnataka, India.
authors.forename: Amandeep
authors.initials: A
authors.lastname: Singh
authors.affiliation: Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, Karnataka, India.
authors.forename: Umesh
authors.initials: U
authors.lastname: Varshney
authors.affiliation: Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012, Karnataka, India. Electronic address: mv@mbu.iisc.ernet.in.
authors.forename: M
authors.initials: M
authors.lastname: Vijayan
mesh_terms: D000595:Amino Acid Sequence / Q000235:genetics; D018360:Crystallography, X-Ray; D004277:DNA, Single-Stranded / Q000737:chemistry* / Q000235:genetics; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure; D008958:Models, Molecular; D020102:Mycobacterium smegmatis / Q000737:chemistry* / Q000235:genetics; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid
chemical_list: D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins
keywords: Inter-subunit clamp; OB fold; Paralogous SSB; Variability in quaternary structure