Insect pheromones Insulin

One of the hallmarks of OBPs is the six cysteine (six half cystines) residues, but this criterion alone is not sufficient to classify a certain protein as olfactory protein. It is important to demonstrate that an OBP is expressed only (or predominantly) in olfactory tissues. Evidence for their ability to bind odorants is also desirable, but not sine qua non. One of these criteria alone would not be enough to define a given protein as an OBP. For example, bovine serum albumin (BSA) binds to insect pheromones (Leal, unpublished data) and yet it is not an OBP because it does not occur in olfactory tissues in the first place. Conversely, a protein specific to antennae is not necessarily an OBP. There are other proteins that may be expressed in antennae but not in control tissues. Non-OBPs specific to insect antennae have been previously detected (Ishida and Leal, unpublished data). Also, a g lu tath i o n e -. S -1 ra n s I e ra s e has been reported to be expressed specifically in antennae of M. sexta (Rogers et al., 1999). Likewise, the six-cysteine criterion should not be misleadingly used. Insulin and bovine pancreatic trypsin inhibitor, for example, have six cysteines in three disulfide bridges and yet they are not odorant-binding proteins. Also, mammalian and insect defensins have six well-conserved cysteine residues. 

Sequence homology has been noted previously (17) between the N-terminus of Hez-PBAN and insulin-like growth factor II, and the C-terminus with the insect peptide leucopyrokinin (Table II) isolated from cockroach heads. The striking similarity of the first 16 residues of the melanization and reddish colorization hormone (MRCH) of B. mori (18) and Bom-PBAN has led to the suggestion by Kitamura ti 1. (17) that they are identical (Table II), thus implying a dual role for this hormone in the larvae (melanization and reddish colorization) and adult moth (pheromone biosynthesis). 

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