Filarial paramyosin: cDNA sequences from Dirofilaria immitis and Onchocerca volvulus

The nucleotide sequence of a cDNA copy of the Dirofilaria immitis paramyosin gene was determined. The sequence was 2545 nucleotides in length, consisting of a single open reading frame of 848 amino acids capable of encoding a protein with a calculated molecular weight of 98,000. The cDNA clone was not complete, but probably includes over 97% of the coding region of the gene. We have previously observed that the cloned D. immitis paramyosin is recognized by sera from humans infected with Onchocerca volvulus. To determine the extent of homology at the protein level, we screened a cDNA library of O. volvulus with an antiserum made against D. immitis paramyosin. Ten recombinant clones were partially sequenced, comprising a total of 1186 nucleotides or 389 amino acids. The amino acid sequence of D. immitis paramyosin was 99% identical to the O. volvulus paramyosin. We also compared the amino acid sequence to other cloned paramyosins, and noted that 92% of the amino acids were identical to those of Caenorhabditis elegans, and 34% identical to those of Schistosoma mansoni. Comparison of the paramyosin sequence between different species revealed a hierarchy of similarities: (1) a 7-amino-acid repeat with apolar residues in the a and d position as the most conserved, followed by (2) the amino acid sequence and (3) the DNA sequence.