Biochemical, molecular, and phylogenetic analysis of pyruvate carboxylase in the yellow fever mosquito, Aedes aegypti.

Pyruvate carboxylase (PC, pyruvate: carbon dioxide ligase [ADP-forming], EC 6.4.1.1) was purified from the yellow fever mosquito, Aedes aegypti. The purified PC showed two polypeptides of similar M(r) (133 and 128 k). The N-terminal sequences of both polypeptides were shown to be very similar, if not identical. A polyclonal antiserum against the 133 kDa polypeptide cross-reacted strongly with the 128 kDa polypeptide. PC was found in all tissues examined. Using a semi-quantitative Western blot assay, PC was shown to be concentrated in the indirect flight muscles and fat body preparations. The ratios of the 133 to 128 kDa polypeptides were shown to differ in various tissues and an Aedes albopictus cell line. The indirect flight muscle was the only tissue in which the 128 kDa polypeptide was more abundant, while both the midgut and the cell line showed almost exclusively the 133 kDa polypeptide. Both peptides were present in varying amounts in brain, malpighian tubule, ovary and fat body preparation. The two isoforms of PC could play different roles in the flight muscle and other tissues. Clones covering a complete cDNA of PC of A. aegypti were obtained using a directional approach. The 3952 bp nucleotide sequence, including a 3585 bp coding region, was determined from these cDNA clones. The deduced 1195 amino acid sequence has a calculated M(r) of 132,200. A putative mitochondrial targeting sequence was determined by comparing the deduced amino acid sequence to the N-terminal sequences of the mature protein. The presence of a mitochondrial targeting sequence indicates that the mosquito PC encoded by the cloned cDNA may be localized in the mitochondria. After the targeting sequence, three functional domains were identified in the following order; biotin carboxylase (BC), carboxyltransferase (CT) and biotin carboxyl carrier protein (BCCP). The mosquito PC showed very high similarity to PCs from other sources (55.1-75.2% identity). Genomic Southern analysis indicated that there could be two similar PC genes or a single PC gene with allelic polymorphism in the A. aegypti genome. The evolutionary relationship of PCs among different organisms was consistent with the accepted evolutionary relationship of their host organisms. The evolution of the domain structures of the biotin-dependent carboxylases including PC was also investigated. This analysis indicates that biotin-dependent carboxylases evolved from a common origin. The analysis also provides evidence for early gene duplication events that shaped the family of biotin-dependent carboxylases. Clear evidence for the coevolution of BC and BCCP domains is presented, although they are associated with very different CT domains and the relative position of the three functional domains varies between members of the biotin-dependent carboxylases.