Monday, December 11, 2006 - 10:35 AM

Molecular switch at the C-terminus of BmorPBP

Wei Xu, wayxu@ucdavis.edu1, Yuko Ishida, yshida@ucdavis.edu1, and Walter S. Leal, wsleal@ucdavis.edu2. (1) University of California - Davis, Entomology, One Shields Avenue, Davis, CA, (2) University of California - Davis, Entomology, One Shields Avenue, Davis, CA

Chemical communication is essential to guide insects’ behaviors. Odorant-detecting sensilla on insect antennae house odorant receptors (Ors), odorant-binding proteins (OBPs) and odorant-degrading enzymes (ODEs). Pheromone-binding proteins (PBPs) are highly accumulated OBPs involved in the transport of pheromones from the outside to the receptors. At the end of the tourway, the pheromone is released by a pH-dependent conformational change of PBP. The C-terminus of Bombyx mori PBP (BmorPBP) is disordered at high pH but forms a á-helix and occupies the binding pocket at the low pH region close to the receptors. We hypothesized that three acidic residues (D132, E137 and E141) at the C-terminus, which are conserved among lepidopteran PBPs, cause this pH-dependent conformational transition. To test this hypothesis, we replaced these three acidic residues in BmorPBP by asparagine and glutamine. After expression and purification of seven mutated BmorPBPs, we analyzed their structures by circular dichroism (CD) and binding activity by a previously described cold binding assay. All mutated BmorPBPs bound bombykol at pH 7 as the native protein. Except for BmorPBPE137Q, all mutated proteins retained binding activity at low pH, indicating that no C-terminus á-helix was formed to compete for the binding site. These results suggest that residues D132 and E141 in BmorPBP contribute to the formation of C-terminus á-helix and the release of ligand at low pH, whereas E137 does not.

Species 1: Lepidoptera Bombycidae Bombyx mori (silkworm)