Catalytic domain of Fungal Halotolerance protein 4-like Serine/Threonine kinases
STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. This subfamily is composed of HAL4, Saccharomyces cerevisiae Ptk2/Stk2, and similar fungal proteins. Proteins in this subfamily are involved in regulating ion transporters. In budding and fission yeast, HAL4 promotes potassium ion uptake, which increases cellular resistance to other cations such as sodium, lithium, and calcium ions. HAL4 stabilizes the major high-affinity K+ transporter Trk1 at the plasma membrane under low K+ conditions, which prevents endocytosis and vacuolar degradation. Budding yeast Ptk2 phosphorylates and regulates the plasma membrane H+ ATPase, Pma1. The HAL4-like subfamily is part of a larger superfamily that includes the catalytic domains of other protein STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.
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