Calcium is the switch in the moonlighting dual function of the ligand-activated receptor kinase phytosulfokine receptor 1

Abstract

BackgroundA number of receptor kinases contain guanylate cyclase (GC) catalytic centres encapsulated in the cytosolic kinase domain. A prototypical example is the phytosulfokine receptor 1 (PSKR1) that is involved in regulating growth responses in plants. PSKR1 contains both kinase and GC activities however the underlying mechanisms regulating the dual functions have remained elusive.FindingsHere, we confirm the dual activity of the cytoplasmic domain of the PSKR1 receptor. We show that mutations within the guanylate cyclase centre modulate the GC activity while not affecting the kinase catalytic activity. Using physiologically relevant Ca2+ levels, we demonstrate that its GC activity is enhanced over two-fold by Ca2+ in a concentration-dependent manner. Conversely, increasing Ca2+ levels inhibits kinase activity up to 500-fold at 100 nM Ca2+.ConclusionsChanges in calcium at physiological levels can regulate the kinase and GC activities of PSKR1. We therefore propose a functional model of how calcium acts as a bimodal switch between kinase and GC activity in PSKR1 that could be relevant to other members of this novel class of ligand-activated receptor kinases.Electronic supplementary materialThe online version of this article (doi:10.1186/s12964-014-0060-z) contains supplementary material, which is available to authorized users.

A Plant Phytosulfokine Peptide Initiates Auxin-Dependent Immunity through Cytosolic Ca2+ Signaling in Tomato

“…Interestingly, prior work with Arabidopsis demonstrated that supplying physiologically relevant concentrations of calcium inhibited PSKR1 kinase activity, while enhancing its GC activity in vitro. These findings suggest that calcium acts as a PSKR1 bimodal switch between the overlapping kinase and GC activities (Muleya et al, 2014). A similar protein structure with dual kinase/GC activities has previously been reported for At-BRI1 (Kwezi et al, 2007) and for Arabidopsis wallassociated kinase-like 10 (Meier et al, 2010), with similar predictions for other kinases.…”

The brassinosteroid receptor BRI1 can generate cGMP enabling cGMP‐dependent downstream signaling

“…When isoleucine takes the place of glycine at position 989, it orientates itself towards an opposing β‐sheet causing increased strain with reduced structural flexibility and also increased the overall hydrophobicity in a compact region at the rear of the protein (Figure b). Such changes may account for the reduced GC activity of the BRI1 815–1196 G989I as structural flexibility in particular is an important feature for multi‐functional proteins to allow the switch from one activation state to another as occurs with PSKR1 (Muleya et al ., ). Notably wild‐type BRI1 has strong autophosphorylation activity resulting in heavily phosphorylated recombinant protein whereas both BRI1 815–1196 Y956F and BRI1 815–1196 G989I being ‘kinase dead’ mutants lack phosphorylated residues (Xu et al ., ; Oh et al ., ).…”

“…The superimposed extracted mass chromatograms of m/z 346.06 [M+H] + ion of cGMP all have the corresponding product ion at m/z 152.06 [M+H] + and this confirmed the presence of cGMP in the reaction mixtures of the respective recombinant BRI proteins (Figure b, c). Similar amounts of cGMP are generated by the recombinant cytoplasmic domain and the full‐length PSKR1 (Kwezi et al ., ; Muleya et al ., , ). It is noteworthy that a recently characterized adenylate cyclase from Arabidopsis (AtKUP7) also has activity resembling that of plant GCs (Al‐Younis et al ., ).…”

“…Using a rationally designed search motif, we identified and experimentally confirmed a number of molecules with guanylate cyclase (GC) activity. Some of these molecules are receptor‐like kinases that have the GC catalytic centre embedded within subdomain IX of the kinase domain and in vitro studies have shown that BRI1 (Kwezi et al ., ), phytosulfokine receptor 1 (PSKR1) (Kwezi et al ., ; Muleya et al ., ) and PePR1 (Qi et al ., ) all have GC activity. In addition, we have since shown that PSKR1 kinase and GC activity is reciprocally modulated by calcium (Muleya et al ., ).…”

Evolutionarily distant pathogens require the Arabidopsis phytosulfokine signalling pathway to establish disease

“…; Muleya et al . ). The binding of Ca 2+ /Calmodulin to PSKR1 is required for receptor activity (Hartmann et al .…”