ABSTRACT
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.
Subject(s)
Antigens, Bacterial/chemistry , Bacterial Proteins/chemistry , Signal Transduction/physiology , Virulence Factors/chemistry , Amino Acid Sequence , Animals , Antigens, Bacterial/metabolism , Antigens, Bacterial/physiology , Bacterial Proteins/metabolism , Bacterial Proteins/physiology , COS Cells , Cell Lineage , Cell Membrane/metabolism , Cells, Cultured , Chlorocebus aethiops , Humans , Mice , Molecular Sequence Data , Monocytes/metabolism , NIH 3T3 Cells , Nuclear Magnetic Resonance, Biomolecular , Protein Binding , Protein Structure, Tertiary , Structure-Activity Relationship , U937 Cells , Virulence Factors/physiologyABSTRACT
The K homology module, one of the most common RNA-binding motifs, is present in multiple copies in both prokaryotic and eukaryotic regulatory proteins. Increasing evidence suggests that self-aggregation of KH modules has a functional role. We have used a combination of techniques to characterize the behavior in solution of the third KH domain of Nova-1, a paradigmatic KH protein. The possibility of working on the isolated module allowed us to observe specifically the homodimerization and RNA-binding properties of KH domains. We provide conclusive evidence that self-association of Nova-1 KH3 occurs in solution even in the absence of RNA. Homodimerization involves a specific protein/protein interface. We also studied the dynamical behavior of Nova-1 KH3 in isolation and in complex with RNA. These data provide a model for the mechanism of KH/RNA recognition and suggest functional implications of dimerization in KH complexes. We discuss our findings in the context of the whole KH family and suggest a generalized mode of interaction.
