title: Mutational analysis of the adeno-associated virus type 2 Rep68 protein helicase motifs.
abstract: The adeno-associated virus type 2 (AAV) Rep78 and Rep68 proteins are required for viral replication. These proteins are encoded by unspliced and spliced transcripts, respectively, from the p5 promoter of AAV and therefore have overlapping amino acid sequences. The Rep78 and Rep68 proteins share a variety of activities including endonuclease, helicase, and ATPase activities and the ability to bind AAV hairpin DNA. The part of the amino acid sequence which is identical in Rep78 and Rep68 contains consensus helicase motifs that are conserved among the parvovirus replication proteins. In the present study, we mutated highly conserved amino acids within these helicase motifs. The mutant proteins were synthesized as maltose binding protein-Rep68 fusions in Escherichia coli cells and affinity purified on amylose resin. The fusion proteins were assayed in vitro, and their activities were directly compared to those of the fusion protein MBP-Rep68 delta, which contains most of the amino acid sequences common to Rep78 and Rep68 and was demonstrated previously to have all of the in vitro activities of wild-type Rep78 and Rep68. Our analysis showed that almost all mutations in the putative helicase motifs severely reduced or abolished helicase activity in vitro. Most mutants also had ATPase activity less than one-eighth of the wild-type levels and lacked endonuclease activity.
authors.affiliation: Laboratory of Molecular and Cellular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892, USA.
authors.forename: S L
authors.initials: SL
authors.lastname: Walker
authors.forename: R S
authors.initials: RS
authors.lastname: Wonderling
authors.forename: R A
authors.initials: RA
authors.lastname: Owens
mesh_terms: D018528:ATP-Binding Cassette Transporters; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000595:Amino Acid Sequence; D002352:Carrier Proteins / Q000235:genetics; D004265:DNA Helicases / Q000235:genetics / Q000378:metabolism*; D004252:DNA Mutational Analysis; D004279:DNA, Viral / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D000229:Dependovirus / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D004720:Endonucleases / Q000378:metabolism; D029968:Escherichia coli Proteins; D015870:Gene Expression; D058619:Maltose-Binding Proteins; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins; D016297:Mutagenesis, Site-Directed; D009711:Nucleotides / Q000494:pharmacology; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014764:Viral Proteins / Q000235:genetics* / Q000378:metabolism*
chemical_list: D018528:ATP-Binding Cassette Transporters; D002352:Carrier Proteins; D004279:DNA, Viral; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D058619:Maltose-Binding Proteins; D009004:Monosaccharide Transport Proteins; D009711:Nucleotides; D011993:Recombinant Fusion Proteins; D014764:Viral Proteins; C461599:maltose transport system, E coli; C068734:rep proteins, Adeno-associated virus 2; D004720:Endonucleases; D000251:Adenosine Triphosphatases; D004265:DNA Helicases