Jocelin Rizo (Mexico City / MX), Carmen Vargas-Lagunas (Mexico City / MX), Jeovanis Gil Valdés (Lund / SE), Ramiro Alonso-Bastida (Mexico City / MX), Angel Gabriel Martínez-Batallar (Mexico City / MX), Magdalena Hernández Ortíz (Mexico City / MX), Sandra Contreras-Martínez (Mexico City / MX), Alma Ruth Reyes González (Mexico City / MX), Noé Arroyo (Mexico City / MX), Sergio Manuel Encarnación-Guevara (Mexico City / MX)
Rhizobium is a type of bacteria found in the rhizosphere that can fix atmospheric nitrogen in association with leguminous plants. Different species have been identified in this genus capable of accumulating poly-beta-hydroxybutyrate (PHB), which is stored in symbiosis and free life.
The process of PHB accumulation typically starts with the condensation of two molecules of acetyl-CoA to form acetoacetyl-CoA. Subsequent reduction and polymerization reactions lead to the production of PHB. This compound serves as a reserve material for carbon and/or electron storage when the bacteria face suboptimal growth conditions. However, the exact role of PHB in the bacteria's metabolism is not fully understood.
Lysine acetylation is a protein modification that plays a crucial role in various cellular processes, such as central metabolism, transcriptional regulation, chemotaxis, and pathogen virulence. It can alter protein functions by affecting DNA binding, enzymatic activity, protein interactions, stability, and localization. In prokaryotes like Rhizobium etli, lysine acetylation occurs both non-enzymatically and through the action of lysine acetyltransferases.
In R. etli, a mutant lacking PHB-synthase (phaC-), and unable to accumulate PHB, shows decreased growth when cultured in a minimal medium with glucose or pyruvate as the sole carbon source. This mutant also exhibits a high excretion of organic acids and an excess of accumulated reducing power. This suggests that PHB synthesis is necessary for R. etli to utilize glycolytic carbon sources for growth. In the absence of PHB synthesis, the accumulation of acetyl-CoA can lead to the chemical acetylation of proteins, which regulates their activity.
This proteomic study using LC-MS/MS is being conducted with R. etli strains of varying PHB accumulation capacities, including the PHB synthase gene mutant, to investigate the regulation of non-enzymatic protein acetylation by PHB synthesis in R. etli. The study aims to determine the target proteins, the stoichiometry of post-translational modifications, and their implications in cellular metabolism under free-living and symbiotic conditions with the legume Phaseolus vulgaris (beans) in the presence or absence of PHB synthesis.
By integrating lysine acetylation stoichiometric analysis with quantitative proteomics, the study has identified and quantified nearly 2000 proteins. Our initial analysis highlighted proteins that participated in carbon metabolism. The results will be shown and discussed.
The research aims to reveal how metabolic processes are affected by the stoichiometry of acetylation under different conditions, providing insights into the regulation of PHB accumulation and its impact on protein acetylation.