Proteolysis during long-term glucose starvation in Staphylococcus aureus COL

A combination of pulse-chase experiments and 2-D PAGE revealed that protein degradation appears to play a crucial role for the cell physiology of Staphylococcus aureus COL during extended periods of glucose starvation. The synthesis rate of virtually all cytosolic and radioactively labeled proteins from growing cells seemed dramatically reduced in the first 3.5 h of glucose starvation. The stability of proteins synthesized in growing cells was monitored by a pulse-chase approach on a proteome wide scale. Especially, enzymes involved in nucleic acid and amino acid biosyntheses, energy metabolism and biosynthesis of cofactors were found rather rapidly degraded within the onset of the stationary phase, whereas the majority of glycolytic and tricarboxylic acid cycle enzymes remained more stable. Furthermore, single enzymes of biosynthetic pathways were differentially degraded. A metabolite analysis revealed that glucose completely depleted from the medium in the transient phase, and amino acids such as alanine and glycine were taken up by the cells in the stationary phase. We suggest that vegetative proteins no longer required in non-growing cells and thus no longer protected by integration into functional complexes were degraded. Proteolysis of putative non-substrate-bound or "unemployed" proteins appears to be a characteristic feature of S. aureus in order to access nutrients as an important survival strategy under starvation conditions.