A 24 kDa parasitism-specific protein from the Caribbean fruit fly, Anastrepha suspensa: cDNA and deduced amino acid...

A 24 kDa parasitism-specific protein (PSP24) was previously reported from the hemolymph of the Caribbean fruit fly, Anastrepha suspensa (Diptera: Tephritidae) after parasitization by the wasp Diachasmimorpha longicaudata (Hymenoptera: Braconidae). This study was designed to sequence the open reading frame of PSP24 and to determine whether it is encoded by the wasp, fruit fly host or by the entomopoxvirus D1EPV which is normally injected into the host with the wasp's egg. Utilizing an existing partial amino acid sequence of PSP24, we obtained two cDNAs by reverse transcription-polymerase chain reaction, from the host hemolymph 48 h post parasitization. The smaller cDNA has an open reading frame (ORF) that encodes 85 amino acids (aa) with a molecular mass of 9711.33 Da and the larger encodes 203 aa with a molecular mass of 23,076 Da. Both cDNAs share a common N-terminus with a signal peptide predictive of secreted proteins, a characteristic that agrees with the observed nature of PSP24. The mature proteins have 39 and 157 aa with deduced molecular masses of 4286.86 Da and 17,651 Da, respectively. Western blots of host hemolymph probed with the anti-PSP24 serum reveal proteins of 0.10 and 0.24 kD, respectively. The discrepancy between the deduced and the observed molecular masses may be explained by their predicted O-linked glycosylation. The amino acid sequences are not homologous with any protein in the available databases. Southern blot hybridization experiments revealed that the proteins are encoded by both the host and the parasite. Furthermore, injection of D1EPV into healthy fruit fly puparia induces the two proteins. Thus, in surprising contrast to an earlier hypothesis that D1EPV encodes PSP24, these results clearly demonstrate that the PSP24 proteins are encoded by wasp and fruit fly but not D1EPV genes. However, their expression is D1EPV induced.