Mutations in the HKD motif of Trypanosoma brucei cardiolipin synthase inhibit cardiolipin synthesis and parasite growth

Phospholipases D (PLDs) are ubiquitous enzymes of the PLD superfamily that catalyze phosphodiester bond cleavage and transphosphatidylation reactions. They are characterized by the presence of two conserved HXK(X) 4 D(X) 6 G(X) 2 N or HKD motifs. While these motifs are essential for catalysis in diverse PLD family members, their functional significance in the bacterial-type cardiolipin synthase of the protozoan parasite Trypanosoma brucei (TbCls) has not yet been investigated. TbCls is essential for parasite survival in culture and contains two conserved HKD motifs in its amino acid sequence. Here we take advantage of a previously constructed cell line in which the endogenous alleles of TbCls were replaced with an inducible ectopic copy of the enzyme, to introduce point mutations in the HKD motifs of TbCls. We found that the HKD motif and its surrounding amino acids are essential for the de-novo synthesis of cardiolipin and for growth of the parasite.