Post-Translational Modifications in Bacteria

Protein post-translational modifications (PTMs) refer to the chemical modifications that occur on proteins after their synthesis through enzymatic or non-enzymatic processes, thereby conferring new structures or functions. Over the past decade, advances in mass spectrometry and multi-omics studies have rapidly expanded the repertoire of bacterial PTMs. Research has shown that these modifications play vital roles in bacterial metabolic regulation, environmental adaptation, persistence, and virulence control, highlighting their significant implications in bacterial physiology and pathogenesis.

Macek, B. et al. Nat Rev Microbiol. 2019.

As research progresses, the types of PTMs identified in bacteria continue to grow, and these modifications have been shown to regulate metabolism, signal transduction, environmental adaptation, and virulence expression. The following are some of the most studied and representative bacterial PTMs.

1. Phosphorylation

Phosphorylation is one of the earliest PTMs discovered in bacteria, mainly occurring on serine, threonine, or tyrosine residues to regulate protein activity and signaling networks. In bacteria, phosphorylation not only acts as an on-off switch in metabolic pathways but also plays a central role in environmental responses. For example, in Escherichia coli, the two-component systems rely on phosphotransfer between histidine kinases and response regulators to rapidly sense and adapt to osmotic stress, nutrient availability, and antibiotic pressure. In Mycobacterium tuberculosis, the serine/threonine kinase family is extensively involved in cell wall synthesis, energy metabolism, and virulence regulation. The reversibility of phosphorylation makes it one of the most flexible regulatory mechanisms in bacteria.

2. Acetylation and Formylation

Protein acetylation is widespread in bacteria, especially ε-amino acetylation of lysine residues. This modification can regulate the activity of metabolic enzymes, alter protein stability, and modulate protein-DNA interactions. For instance, the acetylation network in E. coli involves over 100 metabolic enzymes and directly affects glycolysis, the TCA cycle, and nitrogen metabolism, underscoring its importance in energy and nutrient adaptation. Formylation is typically found at the N-terminal formylmethionine (fMet) of nascent polypeptides, serving as a hallmark of bacterial translation initiation. This modification influences the stability and degradation of new proteins and plays a role in host immune recognition, as mammalian immune systems detect fMet peptides as signals of bacterial infection.

3. Methylation

Protein methylation plays a critical role in bacterial signal transduction and transcriptional regulation. A classic example is the chemotaxis system of E. coli, where methylation of glutamate residues on chemoreceptors modulates sensitivity to chemical gradients, allowing directional movement toward nutrients. Methylation also regulates DNA-binding proteins, affecting transcription factor affinity and specificity. Emerging studies suggest that bacterial protein methylation may be linked to antibiotic resistance and stress responses, pointing to its potential clinical relevance.

4. Pupylation

Pupylation is a unique modification found in actinobacteria such as Mycobacterium, considered a functional analog of ubiquitination in eukaryotes. This process involves the covalent attachment of a small protein Pup (prokaryotic ubiquitin-like protein) to lysine residues of target proteins, tagging them for degradation by proteasome-like complexes. In M. tuberculosis, pupylation is essential for maintaining protein homeostasis by eliminating damaged or unnecessary proteins, thus supporting survival in the host environment. The discovery of pupylation not only revealed a bacterial degradation pathway parallel to ubiquitination but also provided new drug targets for tuberculosis treatment.

5. Lipidation

Lipidation modifications, including palmitoylation and myristoylation, anchor proteins to membranes or enhance protein-membrane interactions. In bacteria, lipidation is critical for secretion systems, membrane protein assembly, and activation of virulence factors. For example, certain pathogenic proteins require lipidation to localize correctly to the bacterial membrane, thereby enhancing infectivity. Although still in its early stages of study, lipidation is increasingly recognized as an important factor in bacterial adaptation to host environments and antibiotic resistance.

6. Glycosylation

Although glycosylation in bacteria has been studied later than in eukaryotes, increasing evidence indicates its importance. For instance, flagellin proteins of Helicobacter pylori are glycosylated to gain structural stability and functionality, which is essential for motility and virulence. Similarly, Pseudomonas aeruginosa relies on glycosylation for maintaining the activity of its virulence factors. These findings highlight that glycosylation, far from being unique to eukaryotes, plays crucial roles in bacterial virulence regulation and host-pathogen interactions.

Bacteria Post-Translational Modifications Research at MtoZ Biolabs

Bacterial PTMs are generally characterized by low abundance and substoichiometric occupancy, with modification levels varying significantly under different environmental conditions. In addition, the distribution of modifying enzymes differs widely across species, leading to diversity and specificity in PTM profiles. These features make bacterial PTMs both central regulators of physiology and challenging targets for detection and functional analysis.