Function of the Yersinia virulence factor YopM
Final Report Abstract
As all currently known effects of Yersinia Yop-effectors act by interacting with and modulating the activity of intracellular host proteins, it seems reasonable to define associating proteins of the host cell in order to understand the molecular mechanism of Yop mediated virulence. The effector YopM is of central importance for the virulence of Yersinia. Deletion of YopM results in a dramatic loss of virulence and a strong increase of the LD50. Despite this importance little is known about the action of this virulence factor. Thus, this project aimed at elucidating the molecular mechanisms that contribute to YopM mediated virulence by identifying and characterizing novel interaction partners. Tandem affinity purification identified RSK1, RSK2, PKN1 and PKN2 as associated proteins. Subsequent experiments from this project revealed that YopM interacts with all members of the RSK and the PKN family of kinases. Furthermore, both RSK and PKN subunits are assembled into one complex with YopM. In agreement with previous reports RSK was shown to be hyperphosphorylated and thereby activated by YopM. It could be shown that RSK hyperphosphorylation results from delayed deactivation by dephosphorylation rather than increased activation of upstream signalling. This effect could also be recapitulated using purified YopM, RSK and phosphatase proteins indicating that delayed dephosphorylation is a direct consequence of the interaction between RSK and YopM presumably by sterically shielding RSK from the action of phosphytases. So far, cellular targets of this over-activation of RSK remain unclear. Furthermore, the effects on PKN subunits are to be defined in the future. The promiscuity of the interaction of YopM with all RSK and all PKN isoforms may point towards an effect independent from the physiological contexts of these two kinases. Functions of RSK and PKN isoforms in the regulation of the immune response are not defined. Interaction with a bacterial effector protein may indicate an important, currently not appreciated role of these molecules during infection of the host organism. Taken together, this project elucidated the molecular events resulting in YopM mediated RSK hyperphosphorylation, a novel mechanism of a bacterial virulence factor. The tandem affinity purification revealed a number of additional potential interaction partners. Verification and characterization of these interactions as well as investigation of the functional consequences are currently ongoing.
Publications
- (2010). Yersinia virulence factor YopM induces sustained RSK activation by interfering with dephosphorylation. PLoS One. 2010 Oct 5;5(10)
Hentschke M, Berneking L, Belmar Campos C, Buck F, Ruckdeschel K, Aepfelbacher M
(See online at https://doi.org/10.1371/journal.pone.0013165)
