Regulation of yeast Yak1 kinase by PKA and autophosphorylation-dependent 14-3-3 binding

Area of Science:

• Cellular biology
• Molecular biology
• Biochemistry

Background:

• Yak1 is a conserved kinase in the DYRK family, acting as a growth antagonist downstream of Ras/PKA signaling.
• Yak1 is known to be phosphorylated by PKA and translocates to the nucleus during nutrient deprivation.
• Regulatory mechanisms governing Yak1 activity and localization remain largely unelucidated.

Purpose of the Study:

• To investigate the roles of Protein Kinase A (PKA) and the 14-3-3 protein Bmh1 in regulating Yak1.
• To elucidate the specific phosphorylation sites and their impact on Yak1 function and localization.
• To understand the interplay between PKA, Bmh1, and Yak1 under different nutrient conditions.

Main Methods:

• Investigated Yak1 regulation by PKA and Bmh1 using biochemical assays.
• Utilized site-directed mutagenesis to identify key phosphorylation and autophosphorylation sites.
• Analyzed Yak1 subcellular localization and kinase activity under various conditions.

Main Results:

• PKA-dependent phosphorylation of Yak1 at Ser295 inhibits its nuclear localization.
• Intramolecular autophosphorylation in the N-terminal domain is crucial for Yak1's full kinase activity.
• Bmh1 binding, dependent on Thr335 and another site, reduces Yak1 catalytic activity without altering localization.

Conclusions:

• PKA-mediated phosphorylation and Bmh1 binding serve as key regulatory mechanisms for Yak1.
• These interactions likely facilitate cytoplasmic retention of inactive Yak1 under nutrient-rich (high glucose) conditions.
• Understanding these pathways provides insights into growth regulation and cellular responses to nutrient availability.