Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/17/2008
Publication Date: 4/30/2008
Citation: Fetterer, R.H., Miska, K.B., Jenkins, M.C., Barfield, R.C., Lillehoj, H.S. 2008. Identification and characterization of a serpin from Emeria acervulina. Journal of Parasitology. 94(6)1269-1274.
Interpretive Summary: Poultry coccidiosis is the result of several different species of a protozoan intestinal parasite which causes considerable annual losses to the poultry industry. The primary control for the disease is through application of medications in the feed as birds are raised in confinement housing. The controls by medications are becoming less effective because of increased resistance to the drugs and less desirable due to concerns about drugs possibly remaining in the meat and within the environment. New control methods are needed. The current research is part of an ongoing effort to characterize genes and proteins that are critical in the development of these intracellular parasites that may contribute to new controls. For the first time a gene coding for a serpin, a protease inhibitor which is a member of a large super-family of proteins that are involved in many important regulatory functions, was characterized in the coccidian parasite Eimeria acervulina. The serpin gene and expressed protein has a function suggesting it is an active inhibitor of parasites proteases. The serpin was distributed in all stages of the parasite studied. Microscopic examination suggests the serpin is distributed in unique granules within the parasite. The parasite serpin, when expressed in bacteria, was without activity against model protease. The results indicate that serpins may play a key role in the biology of the parasite.
Technical Abstract: Serpins are serine protease inhibitors that are widely distributed in metazoans but have not been previously characterized in Eimeria. A serpin from Eimeria acervulina was cloned, expressed and partially characterized. Random screening of an E. acervulina sporozoite cDNA library identified a single clone (D14) whose coding region shared high similarity to consensus structure of single domain serpins. Clone D14 contained an entire open reading frame (ORF) consisting of 1,245 nts that encode a peptide 413 amino acids in length with a predicted molecular weight of 45.5 kDa and containing a signal peptide 28 residues in length. Analysis of the structure predicts that the E. acervulina serpin should be an active inhibitor. However, the recombinant serpin (rbSp) was without inhibitory activity against common serine proteases. By Western blot analysis, polyclonal antiserum to the rbSp recognized a major 53 kDa protein band in unsporulated oocysts and in oocysts sporulated up to 24 hr (fully sporulated). The anti-rbSp detected bands of 52 kDa and 44 kDa in sporozoites (SZ) and merozoites (MZ) respectively. Analysis of MZ secretion products revealed a single protein of 43 kDa which may correspond to secreted serpin. By immuno-staining the serpin was located in granules distributed throughout both the SZ and MZ but granules appeared to be concentrated in the parasite’s anterior. The results demonstrate that E. acervulina contains a serpin gene and expresses a protein with properties similar to active serine protease inhibitor. Although the function of the E. acervulina serpin remains unknown the results further suggest that serpin is secreted by the parasite where it may be involved in cell invasion and other basic developmental processes.