TWENTY-FOURTH ANNUAL EASTERN FISH HEALTH WORKSHOP Royal Pavilion Resort, Atlantic Beach, NC MARCH 9-11, 1999 New Physical Studies of i-Antigen Structure in Ichthyophthirius multifiliis Karin D.E. Everett1, X. Wang1, T.C. Clark3, Y. Lin3, R.C. Orlando2, and H.W. Dickerson1 1Department of Medical Microbiology, College of Veterinary Medicine, University of Georgia, Athens, GA 30602; 2Complex Carbohydrate Research Center, University of Georgia, Athens, GA 30602; 3Department of Microbiology and Immunology, NYSCVM Cornell University, Ithaca, NY 14853 The ciliate, Ichthyophthirius multifiliis parasitizes fresh water fish throughout the world. It expresses a surface i-antigen protein that is recognized by antibodies in the sera and mucus of immune fish. The genes encoding i-antigen have been sequenced in the G1 and G5 serovars of I. multifiliis and the deduced protein sequences are only 22% identical, Nonetheless, these i-antigens retain a distinctive and conserved structural motif: [C-X3-CP]-X19-[C-X2-C]-X20-[C-X2-CP]. Five tandem repeats of this motif are present in the G1 peotein and six tandem repeats are present in the G5 protein. Cysteine repeats are commonly present in iron-binding proteins, zinc-binding proteins, some proteins having the "beta-propeller" structural motif, and the Tetrahymena i-antigen. The regularity of the I. multifiliis repeats is reminiscent of EGF repeats found in EGF-TM7 leukocyte cell-surface proteins and of tandem, disulfide linked SCRs in the decay-accelerating factor that is expressed on cell surfaces exposed to serum complement. The structure of the I. multifiliis protein is being explored using mass spectrometry techniques including MALDI, LC-MS, and LC-MS-MS. MALDI analysis of the G5 antigen has identified a molecular ion of 44,387.4 Daltons. This is the equivalent of the proteolytic removal of 35 AA from the deduced 467-AA protein. The goal of further characterization will be to identify the disulfide crosslinks, covalent modification, posttranslational processing of the G5 i-antigen, and antigenic epitopes. This characterization should lead to the design of an effective vaccine against I. multifiliis. Return to 24th Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page