Structure of Bombyx mori Chemosensory Protein 1 in Solution

S. Jansen¹, J. Chmelík², L. Žídek², P. Padrta², P. Novák², J.-F. Picimbon¹, C. Löfstedt¹ and V. Sklenář²

¹ Lund University, Department of Ecology, SE-22362 Lund, Sweden

² Masaryk University, Faculty of Science, National Centre for Biomolecular Research,

Kotlářská 2, CZ-61137 Brno, Czech Republic

xchmelik@chemi.muni.cz

In insects, two different soluble protein groups have been identified in the antennal lymph. The first group comprises the Odorant Binding Proteins (OBPs). These proteins are approximately 150 residues long and contain six highly conserved cysteines forming three disulfide bridges. They are implied in the binding of pheromones and odorant molecules. The second group is formed by Chemosensory Proteins (CSPs). CSPs are smaller proteins of around 110 amino acids that contain only four cysteines linked by two disulfide bridges, at different positions than those from OBPs. Their signature motif is CX₆CX₁₈CX₂C.

The first proposed role of CSPs was based on their tissue localization. They are mainly expressed in chemosensory sensillae in antennae, legs, proboscis and other chemosensory organs and they have been attributed a role in carrying chemosensory or gustatory molecules. However, no binding to taste or odor molecules has yet been demonstrated. On the other hand, binding to pheromone compounds and fatty acids has been shown in Mamestra brassicae and in Apis mellifera. Moreover, they have a role in solubilizing cuticular hydrocarbons in ants. Thus, the role of CSPs can be extended to carrier proteins for hydrophobic ligands.

Here we report the determination of the structure of Bombyx mori CSP1 (BmorCSP1) by NMR. BmorCSP1 is expressed mainly in antennae and legs and was cloned from antennal cDNA. The overall fold of BmorCSP1 is globular and comprises six α-helices. These helices span residues 10-14, 17-27, 35-49, 57-72, 75-85, and 92-100. The hydrophobic edges of the helices are formed mostly by leucine and isoleucine residues and therefore well suited to constitute a binding site for hydrophobic ligands.