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Catalytic domain of the Serine/Threonine protein kinase, With No Lysine (WNK) 3 STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. WNK3 shows a restricted expression pattern; it is found at high levels in the pituary glands and is also expressed in the kidney and brain. It has been shown to regulate many ion transporters including members of the SLC12A family of cation-chloride cotransporters such as NCC and NKCC2, the renal potassium channel ROMK, and the epithelial calcium channels TRPV5 and TRPV6. WNK3 appears to sense low-chloride hypotonic stress and under these conditions, it activates SPAK, which directly interacts and phosphorylates cation-chloride cotransporters. WNK3 has also been shown to promote cell survival, possibly through interaction with procaspase-3 and HSP70. WNKs comprise a subfamily of STKs with an unusual placement of the catalytic lysine relative to all other protein kinases. The WNK3 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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