Evidence against Translational Repression by the Carboxyltransferase Component of Escherichia coli Acetyl Coenzyme A Carboxylase

Abstract

In Escherichia coli, synthesis of the malonyl coenzyme A (malonyl-CoA) required for membrane lipid synthesis is catalyzed by acetyl-CoA carboxylase, a large complex composed of four subunits. The subunit proteins are needed in a defined stoichiometry, and it remains unclear how such production is achieved since the proteins are encoded at three different loci. Meades and coworkers (G. Meades, Jr., B. K. Benson, A. Grove, and G. L. Waldrop, Nucleic Acids Res. 38:1217-1227, 2010, doi:http://dx.doi.org/ 10.1093/nar/gkp1079) reported that coordinated production of the AccA and AccD subunits is due to a translational repression mechanism exerted by the proteins themselves. The AccA and AccD subunits form the carboxyltransferase (CT) heterotetramer that catalyzes the second partial reaction of acetyl-CoA carboxylase. Meades et al. reported that CT tetramers bind the central portions of the accA and accD mRNAs and block their translation in vitro. However, long mRNA molecules (500 to 600 bases) were required for CT binding, but such long mRNA molecules devoid of ribosomes seemed unlikely to exist in vivo. This, plus problematical aspects of the data reported by Meades and coworkers, led us to perform in vivo experiments to test CT tetramermediated translational repression of the accA and accD mRNAs. We report that increased levels of CT tetramer have no detectable effect on translation of the CT subunit mRNAs.

Interaction of the Nitrogen Regulatory Protein GlnB (PII) with Biotin Carboxyl Carrier Protein (BCCP) Controls Acetyl-CoA Levels in the Cyanobacterium Synechocystis sp. PCC 6803

“…The enzyme is feedback inhibited by acyl-ACP (Jiang and Cronan, 1994) and the catalytic activity of CT is decreased by its own transcript when acetyl-CoA levels are low. Evidence that the CT component additionally represses the translation of the accA/accD mRNA (Meades et al, 2010) has been challenged lately (Smith and Cronan, 2014). Disturbance of ACC regulation has been shown to impact the acetyl-CoA pool (Davis et al, 2000; Zha et al, 2009).…”

The Bacterial signal transduction protein GlnB regulates the committed step in fatty acid biosynthesis by acting as a dissociable regulatory subunit of acetyl‐CoA carboxylase

“…Conversely, when acetyl‐CoA levels are high, CT dissociates from the mRNA enhancing its enzymatic activity and allowing translation of the CT subunits (Meades et al ., ). However, this hypothesis has been recently challenged by Smith and Cronan (). The E. coli MS‐ACC is also subject to feedback inhibition by acylated forms of the acyl carrier protein (acyl‐ACP) (Davis and Cronan, ).…”

Phospholipid synthesis inside phospholipid membrane vesicles

“…This is because CO 2 dissolved in the reaction solution was being converted to HCO 3 − and used for malonyl-CoA synthesis. In total, the net amount of CO 2 (HCO3 - ) remains constant although it was consumed by AccC 32 , because CO 2 was generated from the FA elongation step by FabB or FabH (Supplementary Fig. 13 ).…”