Structural basis of mechanochemical coupling in a hexameric molecular motor.
The P4 protein of bacteriophage phi12 is a hexameric molecular motor closely related to superfamily 4 helicases. P4 converts chemical energy from ATP hydrolysis into mechanical work, to translocate single-stranded RNA into a viral capsid. The molecular basis of mechanochemical coupling, i.e. how small approximately 1 A changes in the ATP-binding site are amplified into nanometer scale motion along the nucleic acid, is not understood at the atomic level. Here we study in atomic detail the mechanochemical coupling using structural and biochemical analyses of P4 mutants. We show that a conserved region, consisting of superfamily 4 helicase motifs H3 and H4 and loop L2, constitutes the moving lever of the motor. The lever tip encompasses an RNA-binding site that moves along the mechanical reaction coordinate. The lever is flanked by gamma-phosphate sensors (Asn-234 and Ser-252) that report the nucleotide state of neighboring subunits and control the lever position. Insertion of an arginine finger (Arg-279) into the neighboring catalytic site is concomitant with lever movement and commences ATP hydrolysis. This ensures cooperative sequential hydrolysis that is tightly coupled to mechanical motion. Given the structural conservation, the mutated residues may play similar roles in other hexameric helicases and related molecular motors.
Institute of Biotechnology and Department of Biological and Environmental Sciences, University of Helsinki, Viikki Biocenter P. O. Box 65, Helsinki FIN-00014, Finland.
Denis E
DE
Kainov
Division of Structural Biology, The Henry Wellcome Building for Genomic Medicine, Oxford University, Roosevelt Drive, Oxford OX3 7BN, United Kingdom.
Erika J
EJ
Mancini
Institute of Biotechnology and Department of Biological and Environmental Sciences, University of Helsinki, Viikki Biocenter P. O. Box 65, Helsinki FIN-00014, Finland.
Jelena
J
Telenius
Institute of Biotechnology and Department of Biological and Environmental Sciences, University of Helsinki, Viikki Biocenter P. O. Box 65, Helsinki FIN-00014, Finland.
Jiří
J
Lísal
Division of Structural Biology, The Henry Wellcome Building for Genomic Medicine, Oxford University, Roosevelt Drive, Oxford OX3 7BN, United Kingdom.
Jonathan M
JM
Grimes
Institute of Biotechnology and Department of Biological and Environmental Sciences, University of Helsinki, Viikki Biocenter P. O. Box 65, Helsinki FIN-00014, Finland.
Dennis H
DH
Bamford
Division of Structural Biology, The Henry Wellcome Building for Genomic Medicine, Oxford University, Roosevelt Drive, Oxford OX3 7BN, United Kingdom. Electronic address: dave@strubi.ox.ac.uk.
David I
DI
Stuart
Institute of Biotechnology and Department of Biological and Environmental Sciences, University of Helsinki, Viikki Biocenter P. O. Box 65, Helsinki FIN-00014, Finland. Electronic address: r.tuma@leeds.ac.uk.
Roman
R
Tuma
D000244:Adenosine Diphosphate / Q000737:chemistry; D000255:Adenosine Triphosphate / Q000737:chemistry; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001435:Bacteriophages / Q000378:metabolism*; D001665:Binding Sites; D002213:Capsid / Q000737:chemistry; D002384:Catalysis; D006868:Hydrolysis; D008954:Models, Biological; D008968:Molecular Conformation; D020409:Molecular Motor Proteins / Q000737:chemistry*; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid; D015678:Viral Structural Proteins / Q000737:chemistry*
D020409:Molecular Motor Proteins; D015678:Viral Structural Proteins; C080832:gp12 protein, Enterobacteria phage T4; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate