title: Antagonistic effects Na+ and Mg2+ on the structure, function, and stability of mycobacteriophage L1 repressor.
abstract: Temperate mycobacteriophage L1 encodes an unusual repressor (CI) for regulating its lytic-lysogenic switching and, in contrast to the repressors of most temperate phages, it binds to multiple asymmetric operator DNAs. Here, ions like Na(+), Cl(-), and acetate(-) ions were demonstrated to facilitate the optimal binding of CI to cognate operator DNA, whereas K(+), Li(+), NH4(+), Mg(2+), carbonate(2-), and citrate(3-) ions significantly affected its operator binding activity. Of these ions, Mg(2+) unfolded CI most severely at room temperature and, compared to Mg(2+), Na(+) provided improved thermal stability to CI. Furthermore, the intrinsic tryptophan fluorescence of CI was changed notably upon replacing Na(+) with Mg(2+) and these opposing effects of Mg(2+) and Na(+) were also noticed in their actions on the C-terminal fragment (CTD) of CI. Taken together, Na(+) appeared to be more appropriate than Mg(2+) for maintaining the biologically active conformation of CI needed for its optimal binding to operator DNA.
authors.affiliation: Department of Biochemistry, Bose Institute, P1/12-CIT Scheme VII M, Kolkata 700 054, India.
authors.forename: Amitava
authors.initials: A
authors.lastname: Bandhu
authors.forename: Tridib
authors.initials: T
authors.lastname: Ganguly
authors.forename: Palas K
authors.initials: PK
authors.lastname: Chanda
authors.forename: Malabika
authors.initials: M
authors.lastname: Das
authors.forename: Biswanath
authors.initials: B
authors.lastname: Jana
authors.forename: Gopal
authors.initials: G
authors.lastname: Chakrabarti
authors.forename: Subrata
authors.initials: S
authors.lastname: Sau
mesh_terms: D000085:Acetates / Q000378:metabolism; D002254:Carbonates / Q000378:metabolism; D002951:Citrates / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism*; D009160:Mycobacteriophages / Q000235:genetics / Q000378:metabolism*; D011487:Protein Conformation; D012097:Repressor Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D014764:Viral Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D000085:Acetates; D002254:Carbonates; D002951:Citrates; D012097:Repressor Proteins; D014764:Viral Proteins; D012964:Sodium; D008274:Magnesium