title: Portal-large terminase interactions of the bacteriophage T4 DNA packaging machine implicate a molecular lever mechanism for coupling ATPase to DNA translocation.
abstract: DNA packaging by double-stranded DNA bacteriophages and herpesviruses is driven by a powerful molecular machine assembled at the portal vertex of the empty prohead. The phage T4 packaging machine consists of three components: dodecameric portal (gp20), pentameric large terminase motor (gp17), and 11- or 12-meric small terminase (gp16). These components dynamically interact and orchestrate a complex series of reactions to produce a DNA-filled head containing one viral genome per head. Here, we analyzed the interactions between the portal and motor proteins using a direct binding assay, mutagenesis, and structural analyses. Our results show that a portal binding site is located in the ATP hydrolysis-controlling subdomain II of gp17. Mutations at key residues of this site lead to temperature-sensitive or null phenotypes. A conserved helix-turn-helix (HLH) that is part of this site interacts with the portal. A recombinant HLH peptide competes with gp17 for portal binding and blocks DNA translocation. The helices apparently provide specificity to capture the cognate prohead, whereas the loop residues communicate the portal interaction to the ATPase center. These observations lead to a hypothesis in which a unique HLH-portal interaction in the symmetrically mismatched complex acts as a lever to position the arginine finger and trigger ATP hydrolysis. Transiently connecting the critical parts of the motor; subdomain I (ATP binding), subdomain II (controlling ATP hydrolysis), and C-domain (DNA movement), the portal-motor interactions might ensure tight coupling between ATP hydrolysis and DNA translocation.
authors.affiliation: Department of Biology, The Catholic University of America, Washington, DC, USA.
authors.forename: Shylaja
authors.initials: S
authors.lastname: Hegde
authors.forename: Victor
authors.initials: V
authors.lastname: Padilla-Sanchez
authors.forename: Bonnie
authors.initials: B
authors.lastname: Draper
authors.forename: Venigalla B
authors.initials: VB
authors.lastname: Rao
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000595:Amino Acid Sequence; D017122:Bacteriophage T4 / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D001665:Binding Sites; D001692:Biological Transport; D036022:Capsid Proteins / Q000378:metabolism*; D042003:DNA Packaging; D004279:DNA, Viral / Q000378:metabolism*; D010450:Endopeptidases / Q000378:metabolism; D023061:Gene Order; D018257:Helix-Loop-Helix Motifs; D006868:Hydrolysis; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D054730:Protein Interaction Domains and Motifs; D016415:Sequence Alignment; D014758:Viral Core Proteins / Q000378:metabolism; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D036022:Capsid Proteins; D004279:DNA, Viral; D014758:Viral Core Proteins; D014764:Viral Proteins; C065038:gp17 protein, Enterobacteria phage T4; C119911:portal protein, Bacteriophage T4; C061379:gp20 protein, bacteriophage T4; D010450:Endopeptidases; C075881:prohead protease, bacteriophage T4; D000251:Adenosine Triphosphatases