FIGURE 1.

Fatty acid (FA) metabolism and acyl-CoA synthetase (ACS) in Giardia intestinalis. (A) Highly streamlined FA metabolism in G. intestinalis based on the genome sequences. This parasite relies on exogenous FA due to the incapability of synthesizing FA de novo. FA are transported into parasite cell by undefined transporters or other mechanisms. FA are activated by ACS immediately or from the FA pool to form FA-CoA thioesters that may be elongated via the ER-associated elongation system (ELO) table before entering subsequent synthetic pathways. The ACS activity may be inhibited by triacsin C. (B) ACS catalyzes a two-step reaction to form FA-CoA thioesters from FA and CoA; (C) Multiple alignments of the five GiACS proteins at the AMP-binding domain conserved in acyl-activating enzymes and ACS signature motif. Residues conserved in all GiACSs are shaded, while those important to the catalytic function and interacting substrates are boxed and marked with asterisks, respectively. Also, see Supplementary Figure S1 for a multiple alignment of the five full-length GiACS protein sequences with annotation of predicted active sites.