| Description | Secretion of virulence factors in Gram-negative bacteria involves transportation of the protein across two membranes to reach the cell exterior [ ]. There have been four secretion systems described in animal enteropathogens, such as Salmonella and Yersinia, with further sequence similarities in plant pathogens like Ralstonia and Erwinia [].The type III secretion system is of great interest, as it is used to transport virulence factors from the pathogen directly into the host cell and is only triggered when the bacterium comes into close contact with the host. The protein subunits of the system are very similar to those of bacterial flagellar biosynthesis [ ]. However, while the latter forms a ring structure to allow secretion of flagellin and is an integral part of the flagellum itself, type III subunits in the outer membrane translocate secreted proteins through a channel-like structure.Exotoxins secreted by the type III system do not possess a secretion signal, and are considered unique for this reason [ ]. Salmonella/Yersinia spp. secrete a protein, SptP, with tyrosine phosphatase activity [, ]. SptP exerts its function by acting as a GTPase-activating protein, and counteracts the effects of SopE []. This is similar to the Yersinia exotoxin YopH, which degrades host cell signal transduction [].X-ray crystal structures of the Yersinia tyrosine phosphatase (PTPase) in complex with tungstate and nitrate have been solved to 2.4A resolution [ ]. The fold belongs to the α-β class. The crystal structure reveals that the nucleophilic cysteine (Cys 403) is positioned at the centre of a distinctive phosphate-binding loop. This loop is at the hub of several hydrogen-bond arrays that not only stabilise a bound oxyanion, but may activate Cys 403 as a reactive thiolate. Binding of tungstate triggers a conformational change that traps the oxyanion and swings Asp 356, an important catalytic residue that resides in a flexible loop, by ~6A into the active site []. | Name | Type III secreted modular tyrosine phosphatase, SptP/YopH |
| Short Name | Tyr_Pase_SptP/YopH | Type | Family |
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