The Eukaryotic Linear Motif resource for
Functional Sites in Proteins
Accession:
Functional site class:
SPAK-OSR1 docking motif
Functional site description:
The Ste20-related proline alanine-rich kinase (SPAK) and oxidative stress response kinase (OSR1) are the only two mammalian serine-threonine kinases belonging to the germinal centre-like kinase subfamily VI. The CCT domain of SPAK/OSR1 proteins represents a novel protein fold called SPOC. The CCT domains of human SPAK-OSR1 are 79% identical at the sequence level and are also highly conserved in other metazoan organisms. The main described function of the CCT domain SPOC fold is to interact with a particular docking site called the RFxV motif in order to bind and phosphorylate the target proteins. The RFxV motif is also found in the upstream activating kinases WNK1 and WNK4 and so it is also used to dock these activating kinases to their SPAK/OSR1 substrates.
ELM Description:
The SPAK and OSR1 kinases specifically recognize their upstream activators and downstream substrates by interacting with their RFxV motifs. The Conserved C-Terminal (CCT) domain of SPAK and OSR1 acts as a binding domain for this interaction. The primary pocket of the CCT domain forms a web of molecular interactions with the Arg, Phe and Val residues of the RFxV-containing peptide and mutation of any of the conserved residues prevents the interaction. Ile is allowed at the V position. Proline is not allowed at the X position due to the backbone contacts it makes in the beta augmentation with the edge beta strand of the CCT. The motif has so far only been found in the Metazoa.
Pattern: RF[^P][IV].
Pattern Probability: 0.0000768
Present in taxon: Metazoa
Interaction Domain:
OSR1_C (PF12202) Oxidative-stress-responsive kinase 1 C terminal (Stochiometry: 1 : 1)
PDB Structure: 2V3S
o See 13 Instances for DOC_SPAK_OSR1_1
o Abstract
OSR1 (oxidative stress-responsive-1) and SPAK (Ste20/Sps1-related proline/alanine-rich kinase) are related kinases belonging to the GCK-VI subfamily of Ste20 group kinases (Lee,2009). They phosphorylate clusters of threonine residues in their best known substrates the Na+ Cl- cotransporters NCC and NKCC2. Both SPAK and OSR1 possess similar architectures: the kinase catalytic domain, followed by a flexible region and then a conserved C-terminal (CCT) domain (Vitari,2006). SPAK has a flexible N-terminal region with an Ala-Pro stretch thought to be a positional targeting module. The CCT domains of OSR1 and SPAK are 79% identical at their sequence level and form a unique fold called SPOC (SPak/Osr1 C-terminus) fold (Villa,2007).
The CCT domain is involved in the interactions of these kinases - not just with their substrates but also their activator kinases - by recognizing the docking motif RFxV (Piechotta,2002), which these all possess. Both SPAK and OSR1 are involved in many cellular process including cell differentiation, cytoskeletal rearrangement, cell proliferation, transformation and most notably are involved in the regulation of ion homeostasis and volume control in mammalian cells. Since mutations in their WNK1 and WNK4 upstream-activating kinases can cause Gordon's syndrome, an inherited disregulation of Na-Cl co-transporters, SPAK/OSR1 are also considered to be a potential therapeutic target for hypertension. Inhibition of these enzymes reduces the activity of the substrates NCC and NKCC2 and thereby reduces renal salt re-absorption and consequent lowering of blood pressure (Richardson,2008).
The structure of the CCT domain consists of four antiparallel beta-strands packed against two large and one smaller alpha helices (2V3S) (Villa,2007). The interface between alpha1 and beta2 creates an elongated, negatively charged groove called the primary pocket while a secondary hydrophobic pocket is formed by the large loop connecting alpha3 and beta4. The CCT domain interacts with its docking motif via the primary pocket with the residues involved in the interaction being identical in both SPAK and OSR1. RFxV motifs with a following Thr/Ser residue are sensitive to inhibition of binding by phosphorylation which causes a steric clash between the phosphate group and the backbone of the CCT domain. It is not yet clear if SPAK and OSR1 kinase activities can themselves autoregulate RFxV interactions.
o 10 selected references:

o 7 GO-Terms:

o 13 Instances for DOC_SPAK_OSR1_1
(click table headers for sorting; Notes column: =Number of Switches, =Number of Interactions)
Acc., Gene-, NameStartEndSubsequenceLogic#Ev.OrganismNotes
Q96J92 WNK4
WNK4_HUMAN
1016 1020 GKPQLVGRFQVTSSKEPAEP TP 3 Homo sapiens (Human)
1 
Q9H4A3 WNK1
WNK1_HUMAN
1957 1961 TTANKVGRFSVSKTEDKITD TP 1 Homo sapiens (Human)
2 
Q9H4A3 WNK1
WNK1_HUMAN
1859 1863 AGVFKMGRFQVSVAADGAQK TP 1 Homo sapiens (Human)
2 
Q9H4A3 WNK1
WNK1_HUMAN
1945 1949 GQPTKVGRFQVTTTANKVGR TP 1 Homo sapiens (Human)
2 
Q9H4A3 WNK1
WNK1_HUMAN
1257 1261 VVHSAGRRFIVSPVPESRLR TP 1 Homo sapiens (Human)
2 
P55017 SLC12A3
S12A3_HUMAN
19 23 DATLCSGRFTISTLLSSDEP TP 1 Homo sapiens (Human)
2 
A6BLY8 Aatk
A6BLY8_MOUSE
1346 1350 SITHISDSDAQSVGGPAAGA TP 3 Mus musculus (House mouse)
1 
A6BLY8 Aatk
A6BLY8_MOUSE
1336 1340 TVSPTPASRFSITHISDSDA TP 3 Mus musculus (House mouse)
1 
Q924N4 Slc12a6
S12A6_MOUSE
14 18 TTKMSSVRFMVTPTKIDDIP TP 4 Mus musculus (House mouse)
1 
P55012 Slc12a2
S12A2_MOUSE
133 137 GSEEAKGRFRVNFVDPAASS TP 2 Mus musculus (House mouse)
2 
P55012 Slc12a2
S12A2_MOUSE
77 81 GPTPSQSRFQVDPVSENAGR TP 2 Mus musculus (House mouse)
2 
P55014 Slc12a1
S12A1_MOUSE
16 20 SVPSSASRFQVHVINEGHGS TP 2 Mus musculus (House mouse)
1 
Q80UE6 Wnk4
WNK4_MOUSE
996 1000 GKPQLVGRFQVTSSKEPAEP TP 2 Mus musculus (House mouse)
1 
Please cite: ELM 2016-data update and new functionality of the eukaryotic linear motif resource. (PMID:26615199)

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