A COOH-terminal domain regulates the activity of Leishmania proton pumps LDH1A and LDH1B

Leishmania donovani requires actively transporting proton efflux pumps to survive the acidic environment of macrophage phagolysosomal vacuoles and to maintain an electrogenic H(+) gradient for nutrient uptake. The L. donovani genome contains a differentially expressed pair of genes, LDH1A and LDH1B, with homology to yeast H(+)-ATPases that are 98% identical in sequence with amino acid differences concentrated at the COOH-terminus (15 of last 37 differ), a region implicated in regulation of yeast and plant proton pumps. Functional complementation of a Saccharomyces cerevisiae strain deficient in endogenous H(+)-ATPase activity, support of yeast growth at low pH, and ability to acidify media demonstrate that LDH1A and LDH1B encode proton pumps. LDH1A and LDH1B encode a COOH-terminal autoinhibitory domain as COOH-truncated peptides support increased rates of growth in yeast, enhanced media acidification, increased enzyme activity (V(max)) and decreased K(m). This regulatory domain mediates differing function properties; LDH1A, but not LDH1B, supports yeast growth at pH 3 and LDH1A shows a greater ability to acidify media. Deletion of the last eight amino acids from LDH1B permits growth at pH 3 and increases media acidification, swapping of the COOH-tails between LDH1A and LDH1B results in LDH1A (with LDH1B tail) unable to support yeast growth at pH 3 and LDH1B (with LDH1A tail) now able to support growth at pH 3. Replacement of the COOH-terminal eight amino acids of LDH1B with those from LDH1A also confers the ability to support growth at pH 3. The complementation system for the Leishmania proton pumps in yeast described here provides a means to dissect the functional properties of the two isoforms, a convenient supply of protein for structural analysis and a model amenable to screening proton pump inhibitors for potential anti-leishmanial therapeutics.