MRJP9, an ancient protein of the honeybee MRJP family with non-nutritional function
Stefan Albert and Jaroslav Klaudiny
Major royal jelly proteins (MRJPs) form a subfamily within a larger Yellow/MRJP family of proteins. Whereas multiple Yellow-like proteins have been found in all insect genomes including honeybee, MRJPs seem to be restricted to honeybees. Eight MRJP proteins, termed MRJP1-8, have been characterized so far. We found that proteomic analyses of bee hypopharyngeal glands and venom sac identified proteolytic fragments of a protein, which might be a novel member of the MRJP family. Using this information and availability of honeybee genome, we cloned the corresponding cDNA and confirmed by sequencing that it encodes an uncharacterized MRJP9 protein. Interestingly, a cDNA coding for a relative of MRJP9 was found in paper wasp EST library. By phylogenetic analyses we show that MRJP9 is an ancient member of the MRJP family, which diverged prior to occurrence of nutritionally valuable nitrogen-rich repeat regions in MRJPs. Identification of MRJP9 in several bee organs, its comparatively low expression levels there, together with the existence of a MRJP-like protein in wasp indicate that it performs function(s) different from larval nutrition. A novel hypothesis on possible role of MRJP9 found in bee venom as a possible immunosensitizing factor contributing to allergy against royal jelly is discussed.