PURIFICATION AND CHARACTERIZATION OF A NOVEL CHEMOREPELLENT RECEPTOR FROM TETRAHYMENA-THERMOPHILA

Chemosensory transduction and adaptation are important aspects of sign al transduction mechanisms in many cell types, ranging from prokaryote s to differentiated tissues such as neurons. The eukaryotic ciliated p rotozoan, Tetrahymena thermophila, is capable of responding to both ch emoattractants (O'Neill et al., 1985; Leick, 1992; Kohidai, Karsa & Cs aba, 1994, 1995) and chemorepellents (Francis & Hennessey, 1995; Kuruv illa, Kim & Hennessey, 1997). An example of a nontoxic, depolarizing c hemorepellent in Tetrahymena is extracellular lysozyme (Francis & Henn essey, 1995; Hennessey, Kim & Satir, 1995). Lysozyme is an effective c hemorepellent at micromolar concentrations, binds to a single class of externally facing membrane receptors and prolonged exposure (10 min) produces specific chemosensory adaptation (Kuruvilla et al., 1997). We now show that this lysozyme response is initiated by a depolarizing c hemoreceptor potential in Tetrahymena and we have purified the membran e lysozyme receptor by affinity chromatography of solubilized Tetrahym ena membrane proteins. The solubilized, purified protein is 42 kD and it exhibits saturable, high affinity lysozyme binding. Polyclonal anti bodies raised against this 42 kD receptor block the in vivo lysozyme c hemoresponse. This is not only the first time that a chemoreceptor pot ential has been recorded from Tetrahymena but also the first time that a chemorepellent receptor has been purified from any unicellular euka ryote.