The Phosphoproteome of the Minimal Bacterium Mycoplasma pneumoniae

Abstract

Mycoplasma pneumoniae belongs to the Mollicutes, the group of organisms with the smallest genomes that are capable of host-independent life. These bacteria show little regulation in gene expression, suggesting an important role for the control of protein activities. We have studied protein phosphorylation in M. pneumoniae to identify phosphorylated proteins. Two-dimensional gel electrophoresis and mass spectrometry allowed the detection of 63 phosphorylated proteins, many of them enzymes of central carbon metabolism and proteins related to host cell adhesion. We identified 16 phosphorylation sites, among them 8 serine and 8 threonine residues, respectively. A phosphoproteome analysis with mutants affected in the two annotated protein kinase genes or in the single known protein phosphatase gene suggested that only one protein (HPr) is phosphorylated by the HPr kinase, HPrK, whereas four adhesion-related or surface proteins were targets of the protein kinase C, PrkC. A comparison with the phosphoproteomes of other bacteria revealed that protein phosphorylation is evolutionarily only poorly conserved. Only one single protein with an identified phosphorylation site, a phosphosugar mutase (ManB in M. pneumoniae), is phosphorylated on a conserved serine residue in all studied organisms from archaea and bacteria to man. We demonstrate that this protein undergoes autophosphorylation. This explains the strong conservation of this phosphorylation event. For most other proteins, even if they are phosphorylated in different species, the actual phosphorylation sites are different. This suggests that protein phosphorylation is a form of adaptation of the bacteria to the specific needs of their particular ecological niche. Molecular & Cellular Proteomics 9:1228 -1242, 2010.Bacteria of the group called Mollicutes are unique among all living organisms because of their small genome that nevertheless allows them to grow independently from any host cell.The two most intensively studied representatives of the Mollicutes are Mycoplasma genitalium and Mycoplasma pneumoniae with genome sizes of 580 and 816 kb, respectively. The approximately 475 protein-coding and 43 RNA-coding genes of M. genitalium define the lower limit of the genetic equipment that permits independent life. The small genomes of the Mollicutes reflect their adaptation to rarely changing ecosystems, such as lung epithelia for M. pneumoniae (1). Furthermore, M. pneumoniae has only limited metabolic capabilities: this bacterium can utilize only a few carbon sources (glucose, fructose, and glycerol) (2), and its only way to produce ATP is by substrate level phosphorylation in glycolysis. The citric acid cycle, respiration, and most anabolic reactions are not carried out by M. pneumoniae (3).M. pneumoniae is a human pathogen that causes usually mild infections such as atypical pneumonia; however, the infections may be severe in children and elderly people. In addition, M. pneumoniae is involved in extrapulmonary complications, such as erythema multiforme and pediatric en...

The Bacterial Phosphoenolpyruvate:Carbohydrate Phosphotransferase System: Regulation by Protein Phosphorylation and Phosphorylation-Dependent Protein-Protein Interactions

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A serine/threonine phosphatase encoded by MG_207 of Mycoplasma genitalium is critical for its virulence

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