Prokaryotes synthesize fatty acids via the type II fatty acid synthesis (FAS) pathway, where acyl carrier protein (ACP) plays a central role by sequestering the growing acyl chain in its internal hydrophobic cavity. As chain length increases, the cavity expands, a process observed in NMR and crystal structure studies. While plastid FAS in plants and Plasmodium falciparum has been well-characterized, mitochondrial FAS remains largely unexplored.
Here, the researchers present NMR studies of mitochondrial acyl-ACP intermediates in Leishmania major (LmACP). The findings reveal that LmACP undergoes minimal conformational changes upon acylation, with structural perturbations limited to helices II and III. CastP analysis of apo-LmACP (PDB 5ZWT) indicates a smaller cavity compared to Escherichia coli ACP (PDB 1T8K), aligning with the observed small chemical shift perturbations. Additionally, C8-LmACP hydrolyzes faster than E. coli ACP, further supporting the presence of a uniquely small cavity.
Structural comparisons highlight distinct differences in helix I and loop I, including residue substitutions: hydrophobic residues in mitochondrial ACPs are replaced with hydrophilic ones in bacterial/plastid ACPs. Notably, mutating Leu 34 (essential for LmACP folding) to Ala—its bacterial counterpart—leads to a complete loss of structure.
Overall, the study reveals unique structural and functional features of LmACP, distinct from prokaryotic and plastid ACPs. Given the high sequence identity, these characteristics may be conserved across mitochondrial ACPs.
Reference:
Dhembla, C., Kumar, A., Arya, R., Kundu, S., & Sundd, M. (2023). Mitochondrial Acyl Carrier Protein of Leishmania major Displays Features Distinct from the Canonical Type II ACP. Biochemistry, 62(23), 3347–3359. https://doi.org/10.1021/acs.biochem.3c00455