Histomonas meleagridis possesses three alpha-actinins immunogenic to its hosts

Histomonas meleagridis is a protozoan parasite known to cause histomonosis (syn. typhlohepatitis) in poultry. Due to the economic losses which the disease entails, there is an urgency to understanding its pathogenesis. In the present investigation, three partial cDNA sequences encoding heterogenic alpha-actinins previously identified for H. meleagridis were completed and characterized. These three H. meleagridis alpha-actinin isoforms were named alpha-actinin1, alpha-actinin2, and alpha-actinin3. Through mRNA analysis, it was possible to estimate their expected complete coding lengths to ca. 1.9kb, 3.5kb, and 3kb, respectively. Protein structure predictions of completed cDNA sequences revealed that the three H. meleagridis alpha-actinins contain two N-terminal calponin homology (CH) domains that bind actin, a central rod domain of varying lengths, and only one C-terminal EF-Hand. The well conserved N- and C-termini of the H. meleagridis alpha-actinins show amino acid identities between 54% and 82.5% to those of the related trichomonad Trichomonas vaginalis. Additionally, all three alpha-actinins were shown to immune-react with turkey antiserum, while only the immune reaction of alpha-actinin2 and alpha-actinin3 was visible using chicken serum. This demonstrates the antigenic potential of alpha-actinins in host animals. The identification of alpha-actinins with varying rod domain lengths within one organism is a relatively new concept, described as yet only for Entamoeba histolytica.