Regulatory mechanism of olfactory reception in olfactory cells

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In this study, we isolated a novel 26 kDa Ca-binding protein named p26olf from frog olfactory epithelium after several chromatographycal steps including phenyl Sepharose, DEAE Sepharose and Mono Q chromatography in addition to gel filtration. The isolated protein was digested with lysyl endopeptidase to obtain proteolytic fragments of p26olf. Based on the amino acid sequence of the fragments analyzed by a protein sequencer, we synthesized a DNA probe and did PCR using cDNA library of the frog olfactory epithelium. We obtained a cDNA clone consisting of 806 bp. Deduced amino acid sequence of this cDNA contained all of the amino acid sequences identified in the peptide fragments. For this reason, we concluded that this cDNA encodes p26olf. It was found that p26olf consists of 217 amino acids with a calculated molecular mass of 24,493 kDa. Homology search analysis showed that the amino acid sequence of the N-terminal half of p26olf exhibits 34.1 % identity to that of bovine S-100beta and the C-terminal half 32.3 % identity to that of bovine S-100 alpha. Since S-100 proteins are functional as form of dimer, p26olf may function similarly as S-100 proteins but in the form of monomer. Northern blot analysis showed that p26olf is expressed in the frog olfactory epithelium as well as in other tissues like lung and spleen. Immunoreactivity of an antibody raised against a p26olf peptide was found in the cilia layr of the olfactory epithelium.Taken together, these results suggest that p26olf is a dimeric form of S-100 protein and is involved in olfactory transduction or adaptation.