Structure and function of the complex formed by the tuberculosis virulence factors CFP-10 and ESAT-6

The secreted Mycobacterium tuberculosis complex proteins CFP-10 and ESAT-6 have recently been shown to play an essential role in tuberculosis pathogenesis. We have determined the solution structure of the tight, 1:1 complex formed by CFP-10 and ESAT-6, and employed fluorescence microscopy to demonstrate specific binding of the complex to the surface of macrophage and monocyte cells. A striking feature of the complex is the long flexible arm formed by the C-terminus of CFP-10, which was found to be essential for binding to the surface of cells. The surface features of the CFP-10.ESAT-6 complex, together with observed binding to specific host cells, strongly suggest a key signalling role for the complex, in which binding to cell surface receptors leads to modulation of host cell behaviour to the advantage of the pathogen.