title: Crystal structure of T7 gene 4 ring helicase indicates a mechanism for sequential hydrolysis of nucleotides.
abstract: We have determined the crystal structure of an active, hexameric fragment of the gene 4 helicase from bacteriophage T7. The structure reveals how subunit contacts stabilize the hexamer. Deviation from expected six-fold symmetry of the hexamer indicates that the structure is of an intermediate on the catalytic pathway. The structural consequences of the asymmetry suggest a "binding change" mechanism to explain how cooperative binding and hydrolysis of nucleotides are coupled to conformational changes in the ring that most likely accompany duplex unwinding. The structure of a complex with a nonhydrolyzable ATP analog provides additional evidence for this hypothesis, with only four of the six possible nucleotide binding sites being occupied in this conformation of the hexamer. This model suggests a mechanism for DNA translocation.
authors.affiliation: Sir William Dunn School of Pathology, University of Oxford, United Kingdom.
authors.forename: M R
authors.initials: MR
authors.lastname: Singleton
authors.forename: M R
authors.initials: MR
authors.lastname: Sawaya
authors.forename: T
authors.initials: T
authors.lastname: Ellenberger
authors.forename: D B
authors.initials: DB
authors.lastname: Wigley
mesh_terms: D017123:Bacteriophage T7; D004265:DNA Helicases / Q000737:chemistry*; D006868:Hydrolysis; D009711:Nucleotides / Q000737:chemistry; D011487:Protein Conformation
chemical_list: D009711:Nucleotides; D004265:DNA Helicases