title: Domain-Swapping Switch Point in Ste20 Protein Kinase SPAK.
abstract: The related protein kinases SPAK and OSR1 regulate ion homeostasis in part by phosphorylating cation cotransporter family members. The structure of the kinase domain of OSR1 was determined in the unphosphorylated inactive form and, like some other Ste20 kinases, exhibited a domain-swapped activation loop. To further probe the role of domain swapping in SPAK and OSR1, we have determined the crystal structures of SPAK 63-403 at 3.1 Å and SPAK 63-390 T243D at 2.5 Å resolution. These structures encompass the kinase domain and different portions of the C-terminal tail, the longer without and the shorter with an activating T243D point mutation. The structure of the T243D protein reveals significant conformational differences relative to unphosphorylated SPAK and OSR1 but also has some features of an inactive kinase. Both structures are domain-swapped dimers. Sequences involved in domain swapping were identified and mutated to create a SPAK monomeric mutant with kinase activity, indicating that monomeric forms are active. The monomeric mutant is activated by WNK1 but has reduced activity toward its substrate NKCC2, suggesting regulatory roles for domain swapping. The structure of partially active SPAK T243D is consistent with a multistage activation process in which phosphorylation induces a SPAK conformation that requires further remodeling to build the active structure.
authors.affiliation: †Department of Pharmacology and ‡Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas 75390, United States.
authors.forename: Clinton A
authors.initials: CA
authors.lastname: Taylor
authors.affiliation: †Department of Pharmacology and ‡Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas 75390, United States.
authors.forename: Yu-Chi
authors.initials: YC
authors.lastname: Juang
authors.affiliation: †Department of Pharmacology and ‡Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas 75390, United States.
authors.forename: Svetlana
authors.initials: S
authors.lastname: Earnest
authors.affiliation: †Department of Pharmacology and ‡Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas 75390, United States.
authors.forename: Samarpita
authors.initials: S
authors.lastname: Sengupta
authors.affiliation: †Department of Pharmacology and ‡Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas 75390, United States.
authors.forename: Elizabeth J
authors.initials: EJ
authors.lastname: Goldsmith
authors.affiliation: †Department of Pharmacology and ‡Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas 75390, United States.
authors.forename: Melanie H
authors.initials: MH
authors.lastname: Cobb
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D018360:Crystallography, X-Ray; D004789:Enzyme Activation; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D011487:Protein Conformation; D054730:Protein Interaction Domains and Motifs; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D010446:Peptide Fragments; D011994:Recombinant Proteins; C486407:Stk39 protein, mouse; C534421:OXSR1 protein, mouse; D017346:Protein Serine-Threonine Kinases