Facilitation of dissociation reaction of nucleotides bound to Mycobacterium tuberculosis DnaA.

Acidic phospholipids have been shown to promote dissociation of bound nucleotides from Mycobacterium tuberculosis DnaA (DnaA(TB)) purified under denaturing conditions [Yamamoto et al., (2002) Modulation of Mycobacterium tuberculosis DnaA protein-adenine-nucleotide interactions by acidic phospholipids. Biochem. J., 363, 305-311]. In the present study, we show that a majority of DnaA(TB) in non-overproducing cells of M. tuberculosis is membrane associated. Estimation of phospholipid phosphorus following chloroform: methanol extraction of soluble DnaA(TB) purified under native conditions (nDnaA(TB)) confirmed the association with phospholipids. nDnaA(TB) exhibited weak ATPase activity, and rapidly exchanged ATP for bound ADP in the absence of any added phospholipids. We suggest that the outcome of intra-cellular DnaA(TB)-nucleotide interactions, hence DnaA(TB) activity, is influenced by phospholipids.