DNA sequence determination and biochemical analysis of the immunogenic protein P36, the lactate dehydrogenase (LDH) of Mycoplasma hyopneumoniae.

The DNA sequence of the gene encoding the early and specific immunogenic protein P36 of Mycoplasma hyopneumoniae has been determined. Comparison of the DNA sequence and the deduced amino acid sequence of P36 with known genes and proteins in data banks indicated that P36 is a L-lactate dehydrogenase (LDH) (EC 1.1.1.27). Biochemical analysis of protein P36 expressed from the cloned gene in Escherichia coli confirmed that P36 has L-lactate dehydrogenase activity. Protein P36 of M. hyopneumoniae therefore is termed LDH and its gene ldh. M. hyopneumoniae LDH was shown to contain the typical domains of LDH of other bacterial species. Immunologically however, we have shown that polyclonal antibodies against M. hyopneumoniae LDH do not cross-react with related LDH and show high specificity for M. hyopneumoniae. The ldh gene is preceded by several typical -10 sequences found in promoters of prokaryotes, but lacks the -35 sequence. Sequences rich in A+T, however, precede the -10 boxes, suggesting that factors involved in transcription initiation and their regulation may be different in M. hyopneumoniae compared to other bacterial species, but the putative ribosome binding site seems to be conserved.