Finding the smoking gun: protein tyrosine phosphatases as tools and targets of unicellular microorganisms and viruses

Protein tyrosine phosphatases (PTPs) are increasingly recognized as important effectors of host-pathogen interactions. Since Guan and Dixon reported in 1990 that phosphatase YopH serves as an essential virulence determinant of Yersinia, the field shifted significantly forward, and dozens of PTPs were identified in various microorganisms and even in viruses. The discovery of extensive tyrosine signaling networks in non-metazoan organisms refuted the moth-eaten paradigm claiming that these organisms rely exclusively on phosphoserine/phosphothreonine signaling. Similarly to humans, phosphotyrosine signaling is thought to comprise a small fraction of total protein phosphorylation, but plays a disproportionately important role in cell-cycle control, differentiation, and invasiveness. Here we summarize the state-of-art knowledge on PTPs of important non-metazoan pathogens (Listeria monocytogenes, Staphylococcus aureus, Porphyromonas gingivalis, Caulobacter crescentus, Yersinia, Synechocystis, Leishmania, Plasmodium falciparum, Entamoeba histolytica, etc.), and focus also at the microbial proteins affecting directly or indirectly the PTPs of the host (Mycobacterium tuberculosis MTSA-10, Bacillus anthracis anthrax toxin, streptococcal β protein, Helicobacter pylori CagA and VacA, Leishmania GP63 and EF-1α, Plasmodium hemozoin, etc.). This is the first review summarizing the knowledge on biological activity and pharmacological inhibition of non-metazoan PTPs, with the emphasis of those important in host-pathogen interactions. Targeting of numerous non-metazoan PTPs is simplified by the fact that they act either as ectophosphatases or are secreted outside of the pathogen. Interfering with tyrosine phosphorylation represents a powerful pharmacologic approach, and even though the PTP inhibitors are difficult to develop, lifting the fog of phosphatase inhibition is of the great market potential and further clinical impact.