• PNAS (Open Acess Article): unambiguous experimental evidence for the role of pheromone-degrading enzymes in the fast inactivation of pheromones.

Introduction

For an insect, the environment contains a myriad of chemical compounds, most of them are physiologically irrelevant (noise) whereas others may be essential because they carry information (semiochemicals) about mate-finding (sex pheromone), food source (kairomones), oviposition site (oviposition attractants), and many other features of the environment. Insects can communicate very well by sending and receiving chemical signals (see chemical communication). While flying en route to a pheromone or other chemical source, insects encounter intermittent signals with stimulus present in broken bursts some tens of milliseconds in duration occurring with intervals of some hundreds of milliseconds (Murlis, 1997). This has led to the development of a remarkable selective, sensitive, and dynamic olfactory system (Kaissling, 2001) (ANIMATION requires Flash).

From the perspective of molecular recognition, there is another complication. Information-carrying small hydrophobic ligands must reach the olfactory receptors (ORs) (Clyne et al., 1999; Vosshall et al., 1999) in order to be transduced into neuronal activities (spikes). However, these ORs are located on islands (the dendrites) in the sensillar lymph and many odorants cannot "swim" (they are water insoluble). Thus, the olfactory processing starts with odorant-binding proteins (OBPs) (Kaissling, 2001) ferrying the ligands to their receptors (ANIMATION requires Flash). Since their discovery (Vogt and Riddiford, 1981), various functions have been suggested for these proteins. OBPs are postulated to solubilize semiochemicals, protect the ligands from degradation, and to participate in fast inactivation of chemical signals. Clearly, most of the ligands need to be solubilized. Recently, it has been demonstrated that the raison d'etre of these proteins is more than to solubilize ligands. In Drosophila melanogaster, an OBP named LUSH is essential for the recognition of a water-soluble semiochemical (ethanol) (Kim and Smith, 2001). On the basis of their binding abilities, OBPs have been considered to play a significant part in the remarkable selectivity of the insect olfactory system, but the literature is also dichotomous (Campanacci et al., 2001) with data suggesting that some OBPs are specific, whereas others may be more "sloppy". The recent identification of OBPs from a primitive termite species, Zootermopsis nevadensis nevadensis (Isoptera) (Ishida et al., 2002) suggests that the PBP-gene family is distributed throughout the Neopteran orders.

We have been studying olfaction in the silkworm moth, Bombyx mori. Male moths are attracted to the female-produced sex pheromone, bombykol. Structural biology studies with the pheromone-binding protein from the silkworm moth indicate that the binding pocket forms a general hydrophobic surface for binding (Sandler et al., 2000) (BOMBYKOL-B rotating ). The ligands (pheromones and other semiochemicals) are released from the PBP-pheromone complexes upon interaction with negatively-charged membrane surfaces, which leads to conformational changes (Leal, 2000; Damberger et al., 2000; Wojtasek and Leal, 1999) Interestingly, a C-terminal sequence which is an extended (unstructured) conformation in the pheromone-PBP complex (Sandler et al, 2000) and in the unligated BmPBP (Lee et al., 2002) rearranges to form a regular -helix that occupies the pheromone-binding pocket (Horst et al., 2001a,b) (BOMBYKOL-A vibrating requires Quicktime), thus "ejecting" the pheromone to the receptor (ANIMATION requires Flash).

References

• Campanacci, V., Krieger, J., Bette, S., Sturgis, J.N., Lartigue, A., Cambillau, C., Breer, H. and Tegoni, M. (2001). Revisiting the specificity of Mamestra brassicae and Antheraea polyphemus pheromone-binding proteins with a fluorescence binding assay. J. Biol. Chem., 276, 20078-20084.
• Clyne, P.J., Warr, C.G., Freeman, M.R., Lessing, D., Kim, J. and Carlson, J.R. (1999). A novel family of divergent seven-transmembrane proteins: Candidate odorant receptors in Drosophila. Neuron, 22, 327-338.
• Damberger, F., Nikonova, L., Horst, R., Peng, G.H., Leal, W.S. and Wuthrich, K. (2000). NMR characterization of a pH-dependent equilibrium between two folded solution conformations of the pheromone-binding protein from Bombyx mori. Protein Science, 9, 1038-1041.
• Horst, R., Damberger, F., Peng, G., Nikonova, L. Leal, W. S. and Wüthrich, K (2001a). NMR assignment of the A form of the pheromone-binding protein of Bombyx mori.” J. Biomol. NMR, 19, 79-80.
• Horst, R., Damberger, F., Luginbuhl, P., Guntert, P., Peng, G., Nikonova, L., Leal, W.S. and Wuthrich, K. (2001b). NMR structure reveals intramolecular regulation mechanism for pheromone binding and release. Proc. Natl. Acad. Sci. USA, 98, 14374-14379.
• Ishida, Y., Chiang, V. P., Haverty, M. I. and Leal, W. S. (2002). Odorant-binding proteins from a primitive termite. J. Chem. Ecol., 28, 1887-1893.
• Kaissling, K.-E. (2001). Olfactory perireceptor and receptor events in moths: A kinetic model. Chem. Senses, 26, 125-150.
• Kim, M.-S. and Smith, D.P. (2001). The invertebrate odorant-binding protein LUSH is required for normal olfactory behavior in Drosophila. Chem. Senses, 26, 195-199.
• Leal, W.S. (2000). Duality monomer-dimer of the pheromone-binding protein from Bombyx mori. Biochem. Biophys. Res. Commun., 268, 521-529.
• Murlis, J. (1997). Odor plumes and the signal they provide. (R. T. Cardé and A. K. Minks, eds.), Insect Pheromone Research: New Directions, (New York: Chapmann & Hall), pp. 221-247.
• Sandler, B.H., Nikonova, L., Leal, W.S. and Clardy, J. (2000). Sexual attraction in the silkworm moth: structure of the pheromone-binding protein-bombykol complex. Chem. Biol., 7, 143-151.
• Vogt, R.G. and Riddiford, L.M. (1981). Pheromone binding and inactivation by moth antennae. Nature, 293, 161-163.
• Vosshall, L.B., Amrein, H., Morozov, P.S., Rzhetsky, A. and Axel, R. (1999). A spatial map of olfactory receptor expression in the Drosophila antenna. Cell, 96, 725-736.
• Wojtasek, H. and Leal, W.S. (1999). Conformational change in the pheromone-binding protein from Bombyx mori induced by pH and by interaction with membranes. J. Biol. Chem., 274, 30950-30956.

Members

Walter S. Leal
(Principal Investigator)

Yuko Ishida
(PostDoc)
Zainulabeuddin (Zain) Syed
(PostDoc)
Armenak (Armen) Margaryan
(Senior Research Scientist)
Tania Morgan
(Graduate Student)
Wei Xu
(Graduate Student)
Ana Lia Parra
(Graduate Student)
Stephanie DeBorde Dickey
(Research Assistant)
Chris Pagan
(Undergraduate Student)
Allison Manko
(Undergraduate Student)

Former Members
Melissa L. Erickson (PGR)
Jennifer Tsuruda (PGR)
Brooke Pannell (Student)
Melissa Hardstone (Student)
Catherine Richardson (Student)
Göde Schüler (PostDoc)
Ning Li (GradStudent)
Vicky Chiang (Student)
Chunpei Wang (Student)
Carol Chen (Student)
Helen Wong (Student)
Chris Bahr (PostDoc)
John Garden
(Senior Research Associate)
Angela Chen (PGR)
Justin Bonetto
(Undergraduate Student)
Shinichi Tebayashi
(Visiting Scientist)

Address

Walter S. Leal
Maeda-Duffey Lab
UC Davis / Entomology see map

Phone: +1-530-752-7755
FAX: +1-530-754-8682
wsleal@ucdavis.edu