Coiled coil chemoreceptors: importance of symmetric interactions between helices for function

DIEGO A. MASSAZZA,; SILVINA A. IZZO; CLAUDIA A. STUDDERT

Puerto Madryn

Congreso; XLVI Reunión Anual Sociedad Argentina de Investigación Bioquímuca y Biología Molecular (SAIB); 2010

Bacterial transmembrane chemoreceptors (MCPs for methyl-accepting chemotaxis protein) transmit extracellular signals to an associated kinase in order to govern the chemotactic behavior of the cell. The highly conserved cytoplasmic domain of MCPs consists in a long alpha-helical hairpin that forms, in the dimer, a four-helix coiled coil bundle. A comparison between MCP sequences from many microorganisms allowed their classification into families based in the presence of symmetric insertions/deletions of seven aminoacids in their cytoplasmic domains. In order to test the importance of proper interaction between the two antiparallel helices within the monomer, we introduced a heptad deletion in the N-helix, the C-helix or both, in symmetric arrangement, of the serine-sensing MCP of E. coli, Tsr. We then tested the effect of these deletions on function and in vivo organization. We observed that the asymmetric constructions lost their function, while the symmetric one retained parcial function and maintained the organization of wild type Tsr. Moreover, point mutations in this latter construction restored full chemotactic abilities. These results suggest the need to preserve symmetric interactions between the antiparallel helices in the monomer, consistent with the observed evolutionary pattern of MCPs. Such interactions might also be relevant in other coiled coil signaling proteins