title: Cysteine 111 affects coupling of single-stranded DNA binding to ATP hydrolysis in the herpes simplex virus type-1 origin-binding protein.
abstract: Herpes simplex virus type-1 origin-binding protein (UL9 protein) initiates viral replication by unwinding the origins. It possesses sequence-specific DNA-binding activity, single-stranded DNA-binding activity, DNA helicase activity, and ATPase activity that is strongly stimulated by single-stranded DNA. We have examined the role of cysteines in its action as a DNA helicase. The DNA helicase and DNA-dependent ATPase activities of UL9 protein were stimulated by reducing agent and specifically inactivated by the sulfhydryl-specific reagent N-ethylmaleimide. To identify the cysteine responsible for this phenomenon, a conserved cysteine in the vicinity of the ATP-binding site (cysteine 111) was mutagenized to alanine. UL9C111A protein exhibits defects in its DNA helicase and DNA-dependent ATPase activities and was unable to support origin-specific DNA replication in vivo. A kinetic analysis indicates that these defects are due to the inability of single-stranded DNA to induce high affinity ATP binding in UL9C111A protein. The DNA-dependent ATPase activity of UL9C111A protein is resistant to N-ethylmaleimide, while its DNA helicase activity remains sensitive. Accordingly, sensitivity of UL9 protein to N-ethylmaleimide is due to at least two cysteines. Cysteine 111 is involved in coupling single-stranded DNA binding to ATP-binding and subsequent hydrolysis, while a second cysteine is involved in coupling ATP hydrolysis to DNA unwinding.
authors.affiliation: Department of Biochemistry, University of Miami School of Medicine, Miami, Florida 33101-6129, USA.
authors.forename: D A
authors.initials: DA
authors.lastname: Sampson
authors.forename: M E
authors.initials: ME
authors.lastname: Arana
authors.forename: P E
authors.initials: PE
authors.lastname: Boehmer
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000409:Alanine / Q000737:chemistry / Q000235:genetics; D000595:Amino Acid Sequence; D003545:Cysteine / Q000378:metabolism*; D004265:DNA Helicases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004261:DNA Replication; D004277:DNA, Single-Stranded / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004229:Dithiothreitol / Q000494:pharmacology; D005033:Ethylmaleimide / Q000494:pharmacology; D006868:Hydrolysis; D007700:Kinetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D017386:Sequence Homology, Amino Acid; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; D014764:Viral Proteins; C064565:UL9 protein, Human herpesvirus 1; D000255:Adenosine Triphosphate; D004265:DNA Helicases; D003545:Cysteine; D005033:Ethylmaleimide; D000409:Alanine; D004229:Dithiothreitol