An Essential DnaB Helicase of Bacillus anthracis : Identification, Characterization, and Mechanism of Action

Abstract

ABSTRACT We have described a novel essential replicative DNA helicase from Bacillus anthracis , the identification of its gene, and the elucidation of its enzymatic characteristics. Anthrax DnaB helicase (DnaB BA ) is a 453-amino-acid, 50-kDa polypeptide with ATPase and DNA helicase activities. DnaB BA displayed distinct enzymatic and kinetic properties. DnaB BA has low single-stranded DNA (ssDNA)-dependent ATPase activity but possesses a strong 5′→3′ DNA helicase activity. The stimulation of ATPase activity appeared to be a function of the length of the ssDNA template rather than of ssDNA binding alone. The highest specific activity was observed with M13mp19 ssDNA. The results presented here indicated that the ATPase activity of DnaB BA was coupled to its migration on an ssDNA template rather than to DNA binding alone. It did not require nucleotide to bind ssDNA. DnaB BA demonstrated a strong DNA helicase activity that required ATP or dATP. Therefore, DnaB BA has an attenuated ATPase activity and a highly active DNA helicase activity. Based on the ratio of DNA helicase and ATPase activities, DnaB BA is highly efficient in DNA unwinding and its coupling to ATP consumption.