Rv3868 (EccA1), an essential component of the Mycobacterium tuberculosis ESX-1 secretion system, is thermostable

Rv3868 (EccA1) is an essential CbxX/CfqX-family ATPase of the Mycobacterium tuberculosis ESX-1 secretion system. Previously, we demonstrated that Rv3868 is composed of two domains; a regulatory N-terminal domain (NT-Rv3868) and an ATP binding C-terminal domain (CT-Rv3868). In the present report, chemical denaturation studies show that electrostatic interactions stabilize the Rv3868. Interestingly, Rv3868 has notable heat stability and retains about 50% of ATPase activity even at 60°C. The C-terminal domain was found to be important for the heat stability as demonstrated by both enzymatic activity assays and thermal denaturation experiments. Furthermore a structure-sequence analysis based on the content of charged and aliphatic amino acids rationalizes the higher propensity of Rv3868 for thermophilic characteristics.