Purification, structural characterization, cloning and immunocytochemical localization of chemoreception proteins from Schistocerca gregaria

Soluble low-molecular-mass protein isoforms were purified from chemosensory organs (antennae, tarsi and labrum) of the desert locust Schistocerca greg aria. Five genes encoding proteins of this group were amplified by PCR from cDNAs of tarsi end sequenced. Their expression products are polypeptide ch ains of 109 amino acids shelling 40-50% sequence identity with putative olf actory proteins from Drosophila melanogaster and Cactoblastis cactorum. Dir ect structural investigation on isoforms purified from chemosensory organs revealed the presence in the expression products of two of the genes cloned . Two additional protein isoforms a ere detected and their molecular struct ure exhaustively characterized. MS analysis of all isoforms demonstrated th at the four cysteine residues conserved in the polypeptide chain were invol ved in disulfide bridges (Cys29-Cys38 and Cys57-Cys60) and indicated the ab sence of any additional post-translational modifications. Immunocytochemist ry experiments, performed with rabbit antiserum raised against the protein isoform mixture, showed selective labelling of the outer lymph in contact s ensilla of tarsi, maxillary palps and antennae. Other types of sensilla wer e not labelled, nor were the cuticle and dendrites of the sensory cells. No binding of radioactively labelled glucose or bicarbonate was detected, in disagreement with the hypothesis that this class of proteins is involved in the CO2-sensing cascade. Our experimental data suggest that the proteins d escribed here could be involved in contact chemoreception in Orthoptera.