Insights into the control of membrane lipid homeostasis in FapR-containing Gram-positive bacteria

NAKAMATSU, LEANDRO; ALBANESI, DANIELA; SCHUJMAN, GUSTAVO E.; MACHINANDIARENA, FEDERICO; DE MENDOZA, DIEGO

Online

Congreso; SAMIGE-SAIB 2020 (Modalidad Virtual); 2020

Asociación Civil de Microbiología General -Sociedad Argentina de Investigación Bioquímica y Biología Molecular

A key aspect in membrane biogenesis is the coordination of fatty acid to phospholipid synthesis rates. In bacteria, fatty acids (FA) are produced by a type II synthase (FASII) consisting of a repeated cycle of reactions. In FASII, all fatty acyl intermediates are covalently linked to the acyl carrier protein (ACP) and shuttled from one enzyme to another. Malonyl-CoA, which is synthetized by the enzyme acetyl-CoA carboxylase (ACC), is an essential lipid intermediate in FA biosynthesis in all living cells. When the acyl-ACPs reach the proper length, they become substrates for the enzymes involved in phospholipid synthesis, in most cases PlsX, PlsY and PlsC. Previously, we proposed that PlsX is a key regulatory point that synchronizes the FASII with phospholipid synthesis in the Gram-positive model Bacillus subtilis. However, understanding the basis of such coordination mechanism remained a challenge in Gram-positive bacteria. Here, we show that the inhibition of fatty acid and phospholipid synthesis caused by PlsX depletion leads to the accumulation of long-chain acyl-ACPs, the end products of FASII. Hydrolysis of the acyl-ACP pool by heterologous expression of a cytosolic thioesterase relieves the inhibition of fatty acid synthesis, indicating that acyl-ACPs are feedback inhibitors of this metabolic route. Unexpectedly, inactivation of PlsX triggers a large increase of malonyl-CoA leading to induction of the fap regulon. This finding discards the hypothesis, proposed for B. subtilis and extended to other Gram-positive bacteria, that acyl-ACPs are feedback inhibitors of the acetyl- CoA carboxylase. Finally, the continuous production of malonyl-CoA during phospholipid synthesis inhibition leads to the coordinated overexpression of the acyl-ACP consuming PlsX and PlsC enzymes and most of the genes involved in FA synthesis, providing an additional mechanism for fine-tuning the coupling between phospholipid and fatty acid production in bacteria with FapR regulation.