Novel cuticular proteins revealed by the honey bee genome

With the completion of the honey bee genome project, a transition is now occurring from the acquisition of gene sequence to understanding the role and context of gene products within the genome. Here we annotated and characterised a cluster of three genes in a GC-rich 11 kb genomic region on the linkage group 4 encoding highly hydrophobic polypeptides (named apidermins; APD 1-3) containing both sequence motifs characteristic of cuticular proteins and distinctly novel features. Five amino acids, Ala, Gly, Leu, Pro and Val, account for 74-86% of their respective sequences with Ala being the most abundant residue (at least 30% of each peptide). A conserved tetra-peptide AAPA/V is found in all three proteins, but none has the 'R and R' signature implicated in chitin binding. Two proteins, APD-1 and APD-2, contain an arginine-rich motif RERR in short non-hydrophobic stretches near the N-terminal of mature proteins and in both proteins tryptophan is the C-terminal residue. All three genes are spliced and highly expressed in a defined spatio-temporal pattern. apd-1 is expressed in the exoskeletal epidermis, but only during a restricted period of a few days of late pupal and early adult life when the cuticle becomes dark. APD2 appears to be a protein of "internal" cuticles and is expressed in the tracheas, oesophagus and stomach, and also in the embryo. The expression of apd-3 partly overlaps with both apd-1 and apd-3, but apd-3 also is uniquely associated with non-pigmented cuticles such as the eye cover and external cuticle of white pupae. This study expands the collection of genes encoding cuticular proteins by three novel and well characterised members.