Cloning and Nucleotide Sequence of a Full-length cDNA Encoding Ascaris suum Malic Enzyme

The nucleotide sequence of a full-length cDNA encoding NAD+-malic enzyme from the parasitic nematode Ascaris suum was determined. The entire sequence of 2269 bases comprises a 5′-leader, a single open reading frame of 1851 bases, and the complete 3′-noncoding region of 340 bases. The first 12 amino acids of the translated sequence are hydrophobic, typical of mitochondrial translocation signals, and do not appear in the purified mature protein. The mature protein contains 605 amino acids and has a molecular mass of 68,478 Da. The amino acid sequences of tryptic peptides from the purified protein and also the N-terminal sequence show excellent correspondence with the translated nucleotide sequence. Comparison of the amino acid sequence of the ascarid protein with the human and rat liver NAD+-malic enzymes reveals highly conserved regions interrupted with long stretches of lesser homologous sequences. Structural motifs such as the putative nucleotide binding domains and also the malate binding site are clearly identified by alignment of the three protein sequences.