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

Background: Helicases play important roles in nucleic acid transactions. Results: Mycobacterial Lhr uses the energy of ATP hydrolysis to drive 3Ј-to-5Ј translocation along single strand DNA and to unwind duplexes en route. Conclusion: Lhr is better at unwinding an RNA:DNA hybrid than a DNA:DNA duplex. Significance: Lhr defines a novel clade of helicases with a signature domain organization.

Genome-wide identification of SF1 and SF2 helicases from archaea

“…The Lhr helicases were first discovered in 1995 as the longest helicase related protein (Lhr); studies showed that Lhr is a non-essential gene in E.coli (Reuven et al, 1995). This helicase remains unstudied until 2013, a recent work from Mycobacterium smegmatis exemplified Lhr as a novel clade of SF2 helicases that was proven by its biochemical specificities and signature domain organization (Reuven et al 1995, Ordonez et al 2013. …”

Mycobacterium tuberculosis DinG Is a Structure-specific Helicase That Unwinds G4 DNA

“…In all of our helicase assays, we found that EcDinG was able to display optimal activity between 10 and 25 nM protein, but MtDinG required Ͼ100 nM protein (substrate/ protein ratio of 1:200). However, it has been shown that mycobacterial enzymes require Ͼ100 nM protein for its optimal activity (32)(33)(34)(35).…”

All motors have to decide is what to do with the DNA that is given them

“…Several of the most commonly used methods of monitoring the translocation of a motor protein are: a) measuring the arrival of the protein at a particular point along the DNA (19)(20)(21)(22)(23)(24); b) detecting the displacement of obstacles from DNA by the translocating motor (25)(26)(27); c) DNA-dependent ATPase activity of the motor (18,22,(27)(28)(29)(30)(31); d) translocation-induced changes in the structure/ topology of the DNA (32,33). While each approach has advantages and disadvantages, addressing the key questions typically involves a combined approach of several of these techniques.…”

“…For example, many motors are believed to form DNA loops during translocation (22)(23)(24)(25)(26). By considering motor efficiency, the distinction between kinetic and physical step-sizes of the translocation mechanism can be elucidated.…”