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Monoclonal antibodies were raised against a recombinant ribosomal P2β protein of Trypanosoma cruzi. One of these reacted with the C terminus of this protein (peptide R13, EEEDDDMGFGLFD) and epitope mapping confirmed that this epitope was the same as the one defined by the serum of immunized mice, and similar to the previously described chronic Chagas' heart disease (cChHD) anti‐P epitope. Western blotting showed that the monoclonal antibody recognized the parasite ribosomal P proteins, as well as the human ribosomal P proteins. Electron microscopy showed that it stained different structures in parasite and human cells. Interestingly, surface plasmon resonance measurements indicated that the affinity for the parasite ribosomal P protein epitope (R13) was five times higher than for its human counterpart (peptide H13, EESDDDMGFGLFD). Since the human epitope contained an acidic region (EESDD) similar to the AESDE peptide recognized by cChHD patients in the second extra‐cellular loop of the human β1‐adrenergic receptor, the biological activity of the antibody was assessed on neonatal rat cardiomyocytes in culture. The monoclonal antibody had an agonist‐like effect. These results, together with the fact that the monoclonal reacted in Western blots with the different isoforms of the heart β1‐adrenergic receptor, confirm the possible pathogenic role of antibodies against the parasite ribosomal P protein based on their cross‐reaction with the human β1‐adrenergic receptor.

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A brain adenylyl cyclase was shown to contain an epitope closely related to that specified by a conserved sequence containing a nucleotide-binding consensus sequence GXXXXGKS and located in the catalytic sites of bacterial, calmodulin-dependent adenylyl cyclases [Goyard, S., Orlando, C., Sabatier, J.-M., Labruyere, E., d'Alayer, J., Fontan, G., van Rietschoten, J., Mock, M., Danchin, A., Ullmann, A., & Monneron, A. (1989) Biochemistry 28, 1964-1967]. A monoclonal antibody, mab 164, produced against a peptide corresponding to this conserved sequence specifically inhibited the Bordetella pertussis adenylyl cyclase. It also specifically inhibited rat and rabbit brain synaptosomal adenylyl cyclases. The extent of inhibition depended upon the type of enzyme purification, reaching 90% for the calmodulin-sensitive species of enzyme and 20-35% for the forskolin-agarose-retained species. The extent of inhibition in a given fraction also depended upon the effector present. mab 164 reacted on Western blots of forskolin-agarose-retained fractions with a 175-kDa component and did not recognize the Gs alpha stimulatory subunit. Consequently, the 175-kDa protein was considered as a good candidate for an adenylyl cyclase catalyst. The adenylyl cyclase activity contained in forskolin-agarose-retained fractions was further purified on calmodulin-Sepharose. On Western blots of such fractions, mab 164 reacted with a 140-kDa protein, a component that appeared to derive from the 175-kDa protein enriched in the previous step. The kcat of this 140-kDa presumptive adenylyl cyclase was estimated to be of the order of 600 s-1.(ABSTRACT TRUNCATED AT 250 WORDS)