title: The Q motif of a viral packaging motor governs its force generation and communicates ATP recognition to DNA interaction.
abstract: A key step in the assembly of many viruses is the packaging of DNA into preformed procapsids by an ATP-powered molecular motor. To shed light on the motor mechanism we used single-molecule optical tweezers measurements to study the effect of mutations in the large terminase subunit in bacteriophage lambda on packaging motor dynamics. A mutation, K84A, in the putative ATPase domain driving DNA translocation was found to decrease motor velocity by approximately 40% but did not change the force dependence or decrease processivity substantially. These findings support the hypothesis that a deviant "Walker A-like" phosphate-binding motif lies adjacent to residue 84. Another mutation, Y46F, was also found to decrease motor velocity by approximately 40% but also increase slipping during DNA translocation by >10-fold. These findings support the hypothesis that viral DNA packaging motors contain an adenine-binding motif that regulates ATP hydrolysis and substrate affinity analogous to the "Q motif" recently identified in DEAD-box RNA helicases. We also find impaired force generation for the Y46F mutant, which shows that the Q motif plays an important role in determining the power and efficiency of the packaging motor.
authors.affiliation: Department of Physics, University of California at San Diego, La Jolla, CA 92093, USA.
authors.forename: James M
authors.initials: JM
authors.lastname: Tsay
authors.forename: Jean
authors.initials: J
authors.lastname: Sippy
authors.forename: Michael
authors.initials: M
authors.lastname: Feiss
authors.forename: Douglas E
authors.initials: DE
authors.lastname: Smith
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism*; D000465:Algorithms; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D010582:Bacteriophage lambda / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D001665:Binding Sites; D053487:DEAD-box RNA Helicases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004279:DNA, Viral / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004706:Endodeoxyribonucleases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D019065:Virus Assembly
chemical_list: D004279:DNA, Viral; D014764:Viral Proteins; D000255:Adenosine Triphosphate; D004706:Endodeoxyribonucleases; C030894:terminase; D000251:Adenosine Triphosphatases; D053487:DEAD-box RNA Helicases
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