title: Mycobacterium smegmatis Lhr Is a DNA-dependent ATPase and a 3'-to-5' DNA translocase and helicase that prefers to unwind 3'-tailed RNA:DNA hybrids.
abstract: We are interested in the distinctive roster of helicases of Mycobacterium, a genus of the phylum Actinobacteria that includes the human pathogen Mycobacterium tuberculosis and its avirulent relative Mycobacterium smegmatis. Here, we identify and characterize M. smegmatis Lhr as the exemplar of a novel clade of superfamily II helicases, by virtue of its biochemical specificities and signature domain organization. Lhr is a 1507-amino acid monomeric nucleic acid-dependent ATPase that uses the energy of ATP hydrolysis to drive unidirectional 3'-to-5' translocation along single strand DNA and to unwind duplexes en route. The ATPase is more active in the presence of calcium than magnesium. ATP hydrolysis is triggered by either single strand DNA or single strand RNA, yet the apparent affinity for a DNA activator is 11-fold higher than for an RNA strand of identical size and nucleobase sequence. Lhr is 8-fold better at unwinding an RNA:DNA hybrid than it is at displacing a DNA:DNA duplex of identical nucleobase sequence. The truncated derivative Lhr-(1-856) is an autonomous ATPase, 3'-to-5' translocase, and RNA:DNA helicase. Lhr-(1-856) is 100-fold better RNA:DNA helicase than DNA:DNA helicase. Lhr homologs are found in bacteria representing eight different phyla, being especially prevalent in Actinobacteria (including M. tuberculosis) and Proteobacteria (including Escherichia coli).
authors.affiliation: Molecular Biology Program, Sloan-Kettering Institute, New York, New York 10065.
authors.forename: Heather
authors.initials: H
authors.lastname: Ordonez
authors.affiliation: Molecular Biology Program, Sloan-Kettering Institute, New York, New York 10065. Electronic address: shuman@ski.mskcc.org.
authors.forename: Stewart
authors.initials: S
authors.lastname: Shuman
mesh_terms: D039903:Actinobacteria / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000737:chemistry; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004247:DNA / Q000737:chemistry; D004265:DNA Helicases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004260:DNA Repair; D004277:DNA, Single-Stranded / Q000737:chemistry; D005990:Glycerol / Q000737:chemistry; D006868:Hydrolysis; D008969:Molecular Sequence Data; D020102:Mycobacterium smegmatis / Q000201:enzymology* / Q000235:genetics; D054730:Protein Interaction Domains and Motifs; D012313:RNA / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D019809:Streptavidin / Q000737:chemistry
chemical_list: D001426:Bacterial Proteins; D004277:DNA, Single-Stranded; D012313:RNA; D000255:Adenosine Triphosphate; D004247:DNA; D019809:Streptavidin; D000251:Adenosine Triphosphatases; D004265:DNA Helicases; D005990:Glycerol
keywords: DNA Helicase; DNA Repair; Enzyme Kinetics; Mycobacteria; Protein Domains
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