title: Structural and mechanistic basis of anti-termination of Rho-dependent transcription termination by bacteriophage P4 capsid protein Psu.
abstract: The conserved bacterial transcription terminator, Rho, is a potent target for bactericidal agents. Psu, a bacteriophage P4 capsid protein, is capable of inducing anti-termination to the Rho-dependent transcription termination. Knowledge of structural and mechanistic basis of this anti-termination is required to design peptide-inhibitor(s) of Rho from Psu. Using suppressor genetics, cross-linking, protein foot-printing and FRET analyses, we describe a conserved disordered structure, encompassing 139-153 amino acids of Rho, as the primary docking site for Psu. Also a neighbouring helical structure, comprising 347-354 amino acids, lining its central channel, plays a supportive role in the Rho-Psu complex formation. Based on the crystal structure of Psu, its conformation in the capsid of the P4 phage, and its interacting regions on Rho, we build an energy-minimized structural model of the Rho:Psu complex. In this model, a V-shaped dimer of Psu interacts with the two diagonally opposite subunits of a hexameric Rho, enabling Psu to form a 'lid' on the central channel of the latter. We show that this configuration of Psu makes the central channel of Rho inaccessible, and it causes a mechanical impediment to its translocase activity.
authors.affiliation: Laboratory of Transcription Biology, Center for DNA Fingerprinting and Diagnostics, Tuljaguda complex, 4-1-714 Mozamjahi Road, Nampally, Hyderabad 500 001, India.
authors.forename: Amitabh
authors.initials: A
authors.lastname: Ranjan
authors.forename: Savita
authors.initials: S
authors.lastname: Sharma
authors.forename: Ramanuj
authors.initials: R
authors.lastname: Banerjee
authors.forename: Udayaditya
authors.initials: U
authors.lastname: Sen
authors.forename: Ranjan
authors.initials: R
authors.lastname: Sen
mesh_terms: D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors; D036022:Capsid Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics; D003432:Cross-Linking Reagents; D003545:Cysteine / Q000737:chemistry; D004492:Edetic Acid / Q000031:analogs & derivatives / Q000737:chemistry; D031541:Fluorescence Resonance Energy Transfer; D008958:Models, Molecular; D009154:Mutation; D023302:Protein Footprinting; D012234:Rho Factor / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D061806:Transcription Termination, Genetic
chemical_list: D036022:Capsid Proteins; D003432:Cross-Linking Reagents; D012234:Rho Factor; C074513:polarity suppression factor, bacteriophage P4; C042007:1-(4-bromoacetamidobenzyl)EDTA; D004492:Edetic Acid; D000251:Adenosine Triphosphatases; D003545:Cysteine