A specific protein-protein interaction accounts for the in vivo substrate selectivity of Ptp3 towards the Fus3 MAP kinase

Abstract

The mitogen-activated protein kinases (MAPKs) play critical roles in many signal transduction processes. Several MAPKs have been found in Saccharomyces cerevisiae, including Fus3 in the mating pathway and Hog1 in the osmotic-stress response pathway. Cells lacking Fus3 or Hog1 activity are deficient in mating or adaptation to osmotic shock, respectively. However, constitutive activation of either Fus3 or Hog1 is lethal. Therefore, yeast cells have to tightly regulate both the activation and inactivation of Fus3 and Hog1 MAPKs, which are controlled mainly by phosphorylation and dephosphorylation. Previous studies have shown that Fus3 activity is negatively regulated by protein tyrosine phosphatase Ptp3. In contrast, the Hog1 MAPK is mainly dephosphorylated by Ptp2 even though the two phosphatases share a high degree of sequence similarity. To understand the mechanisms of MAPK regulation, we examined the molecular basis underlying the in vivo substrate specificity between phosphatases and MAPKs. We observed that the amino-terminal noncatalytic domain of Ptp3 directly interacts with Fus3 via CH2 ( Cdc25 homology) domain conserved among yeast PTPases and mammalian MAP kinase phosphatases and is responsible for the in vivo substrate selectivity of the phosphatase. Interaction between Ptp3 and Fus3 is required for dephosphorylation and inactivation of Fus3 under physiological conditions. Mutations in either Ptp3 or Fus3 that abolish this interaction cause a dysregulation of the Fus3 MAPK. Our data demonstrate that the specificity of MAP kinase inactivation in vivo by phosphatases is determined by specific protein-protein interactions outside of the phosphatase catalytic domain.

Reciprocal Regulation between Slt2 MAPK and Isoforms of Msg5 Dual-specificity Protein Phosphatase Modulates the Yeast Cell Integrity Pathway

“…Although the functional significance of these motifs remains unknown, it has been proposed that they could be involved in the association with MAPKs (41). In support of this hypothesis, the yeast tyrosine phosphatase Ptp3 has been shown to interact with the MAPK Fus3 through the CH2 domains (42). Recently, a basic motif-based docking domain, present in different types of MAPK-interacting proteins, has been shown to be involved in their association with MAPKs (43).…”

A walk-through of the yeast mating pheromone response pathway

“…In the yeast mating pathway, putative D-sites are also been found in Gpa1 Gα [102], the Ptp3 phosphatase [154], and the Dig1 and Dig2 transcriptional regulators [79]. Hence, D-sites appear to be portable, modular motifs that mediate the interaction of MAPKs with multiple binding partners, contributing to both signal transmission and specificity.…”

Regulation of the Saccharomyces cerevisiae Slt2 Kinase Pathway by the Stress-inducible Sdp1 Dual Specificity Phosphatase

“…It remains to dissect out specific roles of these phosphatases in regulation of Slt2 and other target kinases. It has been shown that protein-protein interaction through amino-terminal noncatalytic domains of Ptp2 and Ptp3 determines their substrate specificity toward Hog1 and Fus3 (40). In addition, the localization of phosphatases could affect their specificity toward various MAPKs.…”