Characterization and cloning of a Tenebrio molitor hemolymph protein with sequence similarity to insect odorant-binding proteins

The yellow mealworm beetle, Tenebrio molitor, produces a number of moderate ly abundant low molecular weight hemolymph proteins (similar to 12 kDa) whi ch behave in a similar manner during purification and share antigenic epito pes. The cDNA sequence of the major component (THP12) was determined and th e deduced protein sequence was found to be similar to those of insect odora nt-binding proteins. Southern blot analysis suggests that at least some of the diversity in this family of proteins is encoded at the gene level. Both northern and western blot analysis indicate that THP12 is present in a var iety of developmental stages and both sexes. THP12 was originally classifie d as an antifreeze protein, but the lack of antifreeze activity in the reco mbinant protein, as well as the clear separation of the antifreeze activity from THP12 following HPLC purification, has ruled out this function. The a bundance of THP12, the similarity of THP12 to insect odorant-binding protei ns, and the presence of hydrophobic cavities inside the protein (Rothemund et al., A new class of hexahelical insect proteins revealed as putative car riers of small hydrophobic ligands. Structure, 7 (1999) 1325-1332.) suggest that THP12 may function to carry non-water soluble compounds in the hemoly mph. THP12 is also similar, particularly in structurally important regions, to other insect proteins from non-sensory tissues, suggesting the existenc e of a large family of carrier proteins which may perform diverse functions throughout the insect. (C) 2001 Elsevier Science Ltd. All rights reserved.