HUMAN CARDIAC TROPONIN-I - PRECISE IDENTIFICATION OF ANTIGENIC EPITOPES AND PREDICTION OF SECONDARY STRUCTURE

The presence of human cardiac troponin I (hcTnI) in serum is considere d to be a highly specific biochemical marker of acute myocardial infar ction. To better understand the antigenic properties of hcTnI, a set o f 68 overlapping peptides covering the complete amino acid sequence of hcTnI was prepared and used in epitope mapping experiments. All 16 an ti-hcTnI monoclonal antibodies tested were found to recognize a peptid e epitope, indicating that recognition by anti-hcTnI monoclonal antibo dies was not dependent on the tertiary structure of the protein. Furth ermore, the peptide reactivity with anti-hcTnI polyclonal antibodies i ndicated that most of the sequence of the protein was antigenic; in pa rticular, the N- and C-terminal extremities were found to be the stron gest antigenic regions. By using accurate secondary structure predicti on methods, hcTnI was found to be an all-alpha type protein, with five regions predicted as helices. Matching the results of the epitope ana lysis with the structural prediction led us to the view that hcTnI is not a globular protein but probably adopts an extended conformation, a llowing a large part of the amino acid sequence of this molecule to be recognized by the immune system. This improved knowledge of the antig enic and structural properties of hcTnI may help in developing new ant ibodies and immunoassays for use in diagnosing myocardial infarction.