The Role of Post-Translational Modifications in Bacterial Responses to Methylglyoxal

Project Summary and Abstract
Methylglyoxal (MGO) is a highly reactive, toxic molecule that is produced non-enzymatically during central
metabolism by virtually all cells. Some microorganisms, including enteric bacteria such as Escherichia coli, also
enzymatically produce MGO during metabolic shifts in order to mitigate phosphorylated sugar toxicity. Although
its production serves to protect E. coli, MGO also directly damages cells, in part through targeted modification
(glycation) of proteins. In Eukaryotes, glycation has been shown to modulate the enzymatic activity of certain
proteins, which in some cases increases cellular protection from MGO-induced stress. Whether glycation serves
a similar function in bacteria is not known. It has been shown, however, that E. coli protects itself from MGO via
detoxification to lactate, a process that also activates a potassium (K+)/proton (H+) antiporter, leading to
cytoplasmic acidification. In addition to these known mechanisms, my preliminary data suggest a role for the
Nitrogen-Related Phosphotransferase System (PTSNtr) in protection from MGO exposure. The PTSNtr protein
PtsN regulates activity of several K+ transporters in a phosphorylation-dependent manner. My preliminary results
show that deleting ptsN confers a survival advantage during MGO exposure, while knocking out PtsO, the protein
that phosphorylates PtsN, decreases survival. However, the pathway and underlying mechanism for this
behavior are not known. I hypothesize that post-translational modifications (phosphorylation of the PTSNtr
and protein glycation) mediate novel mechanisms of MGO protection in E. coli. Aim 1 will delineate the
mechanism underlying the MGO survival advantage of a ΔptsN mutant and determine the contribution of PtsN
phosphorylation to this phenotype, revealing a new role for this conserved phosphotransferase system. Aim 2
will characterize protein glycation targets and changes in protein expression in response to MGO. This will
provide, for the first time, a global view of proteins glycated by MGO in bacteria, the effects of glycation on
protection from MGO stress, and the bacterial regulatory response following exposure to MGO. Completion of
this project will elucidate a new role of posttranslational modification – both phosphorylation of PtsN and glycation
of select proteins – in E. coli survival during MGO stress. It may also reveal novel protective pathways that can
be modulated to combat bacterial infection and inflammation and modulate the host microbiome.

Grant Number: 5F31GM154412-02
NIH Institute/Center: NIH
Principal Investigator: Sara Alexander