DNA-stimulated ATPase activity on the lon (CapR) protein

Area of Science:

• Molecular Biology
• Biochemistry
• Microbiology

Background:

• The CapR protein, encoded by the lon (capR) locus in Escherichia coli, is known as an ATP hydrolysis-dependent protease and a non-specific nucleic acid-binding protein.
• Previous research has established its roles in protein degradation and DNA binding.

Purpose of the Study:

• To investigate a potential novel enzymatic activity of the CapR protein.
• To characterize the DNA-stimulated ATPase activity of CapR and its relationship to its known functions.

Main Methods:

• In vitro assays were used to measure ATP hydrolysis by the CapR protein.
• The effects of DNA (supercoiled, relaxed, double-stranded, single-stranded), RNA, divalent cations, and pH on ATPase activity were assessed.
• The impact of a mutationally altered CapR protein (CapR9) on ATPase activity was examined.

Main Results:

• The CapR protein exhibits DNA-stimulated adenosine triphosphatase (ATPase) activity, distinct from its protease-associated ATPase activity.
• This ATPase activity occurs independently of proteolytic substrates, requires divalent cations, and has a pH optimum of 8.0.
• Supercoiled DNA maximally stimulated ATP hydrolysis, while other DNA forms were less effective, and RNA was inactive. The CapR9 protein inhibited this activity, suggesting an oligomeric nature of CapR in the presence of DNA.

Conclusions:

• The CapR protein possesses a novel, DNA-dependent ATPase activity that is regulated by nucleic acids.
• This finding suggests that nucleic acids may play a regulatory role in the overall functions of the lon (capR) gene product.