title: Evidence for an electrostatic mechanism of force generation by the bacteriophage T4 DNA packaging motor.
abstract: How viral packaging motors generate enormous forces to translocate DNA into viral capsids remains unknown. Recent structural studies of the bacteriophage T4 packaging motor have led to a proposed mechanism wherein the gp17 motor protein translocates DNA by transitioning between extended and compact states, orchestrated by electrostatic interactions between complimentarily charged residues across the interface between the N- and C-terminal subdomains. Here we show that site-directed alterations in these residues cause force dependent impairments of motor function including lower translocation velocity, lower stall force and higher frequency of pauses and slips. We further show that the measured impairments correlate with computed changes in free-energy differences between the two states. These findings support the proposed structural mechanism and further suggest an energy landscape model of motor activity that couples the free-energy profile of motor conformational states with that of the ATP hydrolysis cycle.
authors.affiliation: 1] Department of Physics, University of California, 9500 Gilman Drive, La Jolla, San Diego, California 92093-0379, USA [2] Department of Chemistry and Biochemistry, University of California, San Diego, California 92093-0379, USA [3].
authors.forename: Amy D
authors.initials: AD
authors.lastname: Migliori
authors.affiliation: 1] Department of Physics, University of California, 9500 Gilman Drive, La Jolla, San Diego, California 92093-0379, USA [2].
authors.forename: Nicholas
authors.initials: N
authors.lastname: Keller
authors.affiliation: Department of Biology, The Catholic University of America, 620 Michigan Avenue NE, Washington, District of Columbia 20064, USA.
authors.forename: Tanfis I
authors.initials: TI
authors.lastname: Alam
authors.affiliation: Department of Biology, The Catholic University of America, 620 Michigan Avenue NE, Washington, District of Columbia 20064, USA.
authors.forename: Marthandan
authors.initials: M
authors.lastname: Mahalingam
authors.affiliation: Department of Biology, The Catholic University of America, 620 Michigan Avenue NE, Washington, District of Columbia 20064, USA.
authors.forename: Venigalla B
authors.initials: VB
authors.lastname: Rao
authors.affiliation: Department of NanoEngineering, University of California, 9500 Gilman Drive, La Jolla, San Diego, California 92093-0448, USA.
authors.forename: Gaurav
authors.initials: G
authors.lastname: Arya
authors.affiliation: Department of Physics, University of California, 9500 Gilman Drive, La Jolla, San Diego, California 92093-0379, USA.
authors.forename: Douglas E
authors.initials: DE
authors.lastname: Smith
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D017122:Bacteriophage T4 / Q000502:physiology*; D001696:Biomechanical Phenomena; D042003:DNA Packaging / Q000502:physiology*; D006868:Hydrolysis; D008954:Models, Biological; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D020409:Molecular Motor Proteins / Q000502:physiology*; D016297:Mutagenesis, Site-Directed; D055672:Static Electricity; D014764:Viral Proteins / Q000737:chemistry / Q000502:physiology*
chemical_list: D020409:Molecular Motor Proteins; D014764:Viral Proteins; C065038:gp17 protein, Enterobacteria phage T4; D000255:Adenosine Triphosphate