Genome-Wide Analysis of the Odorant-Binding Protein Gene Family in Drosophila melanogaster

Abstract

Olfaction is of considerable importance to many insects in behaviors critical for survival and reproduction, including location of food sources, selection of mates, recognition of colony con-specifics, and determination of oviposition sites. An ubiquitous, but poorly understood, component of the insect's olfactory system is a group of odorant-binding proteins (OBPs) that are present at high concentrations in the aqueous lymph surrounding the dendrites of olfactory receptor neurons. OBPs are believed to shuttle odorants from the environment to the underlying odorant receptors, for which they could potentially serve as odorant presenters. Here we show that the Drosophila genome carries 51 potential OBP genes, a number comparable to that of its odorant-receptor genes. We find that the majority (73%) of these OBP-like genes occur in clusters of as many as nine genes, in contrast to what has been observed for the Drosophila odorant-receptor genes. Two of the presumptive OBP gene clusters each carries an odorant-receptor gene. We also report an intriguing subfamily of 12 putative OBPs that share a unique C-terminal structure with three conserved cysteines and a conserved proline. Members of this subfamily have not previously been described for any insect. We have performed phylogenetic analyses of the OBP-related proteins in Drosophila as well as other insects, and we discuss the duplication and divergence of the genes for this large family.

Olfactory regulation of mosquito–host interactions

“…In addition, there are 16 atypical AgOBP genes encoding considerably larger proteins of 35 kDa, which have an extended C-terminal region with several other conserved cysteine residues. Lastly, 12 distinct AgOBP genes corresponding to the Plus-C subfamily (Hekmat-Scafe et al, 2002) have been cataloged from the An. gambiae genome (Xu et al, 2003).…”

Molecular evolution of the major chemosensory gene families in insects

“…In D. melanogaster, diverse OBPs are synthesised in the same supporting cells and then secreted to a Insect chemosensory gene family evolution A Sánchez-Gracia et al restricted group of specialised sensilla. Moreover, the same OBPs can be expressed in several types of olfactory hairs and even in non-sensory tissues (Galindo and Smith, 2001;Shanbhag et al, 2001;Hekmat-Scafe et al, 2002). In contrast, olfactory and gustatory receptors are expressed in a much more precise pattern, with each sensory neuron deterministically expressing only a few specific chemoreceptor genes (generally not more than two).…”

“…The chromosomal clustering of OBP genes, first observed in D. melanogaster (Galindo and Smith, 2001;Hekmat-Scafe et al, 2002;Vogt et al, 2002) occurs in all 12 Drosophila genomes (Vieira et al, 2007) (Figure 3). In Drosophila, 69% of OBP genes are arranged in 10 clusters of 2-6 genes; this organisation is significantly more conserved across the genus than expected by chance (Vieira and Rozas, unpublished results).…”

“…The Classic OBPs have been further divided into other subgroups, including the Minus-C group (usually with only four cysteines) and the Dimer OBPs (large OBP proteins formed by two consecutive Minus-C OBP domains) (Hekmat-Scafe et al, 2002). In contrast, Drosophila CSPs form a single conserved class of binding proteins with only four members in Drosophila.…”

Crystal and Solution Studies of the “Plus-C” Odorant-binding Protein 48 from Anopheles gambiae

“…The Plus-C OBPs were first reported in Drosophila and Anopheles (9,17) and recently to the pea aphid Acyrthosiphon pisum (Hemiptera) (18) indicating that protein evolution occurred before the divergence of diptera from other species; therefore, these proteins may also be present in other insect orders. The Anopheles gambiae Plus-C OBPs are distinguished from the other classes by their longer sequences and the presence of 12 cysteines in conserved positions, six of which correspond closely to the conserved cysteines residues of the classic OBPs (8,19).…”