Phosphorylation of the dimeric cytoplasmic domain of the phytosulfokine receptor, PSKR1

Phytosulfokines (PSKs) are plant peptide hormones that co-regulate plant growth, differentiation and defense responses. PSKs signal through a plasma membrane localized leucine-rich repeat receptor-like kinase (phytosulfokine receptor 1, PSKR1) that also contains a functional cytosolic guanylate cyclase with its cyclase catalytic center embedded within the kinase domain. To functionally characterize this novel type of overlapping dual catalytic function, we investigated the phosphorylation of PSKR1 in vitro. Tandem mass spectrometry of the cytoplasmic domain of PSKR1 (PSKR1cd) revealed at least 11 phosphorylation sites (8 serines, 2 threonines and 1 tyrosine) within the PSKR1cd. Phosphomimetic mutations of three serine residues (Ser686, Ser696 and Ser698) in tandem at the juxta-membrane position resulted in enhanced kinase activity in the on-mutant that was suppressed in the off-mutant, but both mutations reduced guanylate cyclase activity. Both the on and off phosphomimetic mutations of the phosphotyrosine (Tyr888) residue in the activation loop suppressed kinase activity, while neither mutation affected guanylate cyclase activity. Size exclusion and analytical ultracentrifugation analysis of the PSKR1cd suggest that it is reversibly dimeric in solution, which was further confirmed by biflourescence complementation. Taken together, these data suggest that in this novel type of receptor domain architecture, specific phosphorylation and dimerization are possibly essential mechanisms for ligand-mediated catalysis and signaling.

The state of the guanylate cyclase mechanism of vasodilatation before and after thyroidectomy in the patients presenting with toxic goiter

The state of the guanylate cyclase activity of myocytes was evaluated from the increment in the diameter of the brachial artery in response to the exogenous administration of nitroglycerin (#D^NO) in 64 samples obtained from 44 patients. A total of 23 studies were carried out during thyrotoxicosis decompensation, 28 ones in the phase of medicamental thyrotoxicosis, and 13 within 5-6 days after thyroidectomy. The guanylate cyclase activity of myocytes was found to correlate with the production of vascular endothelium factors. Thyroidectomy in the patients with toxic goiter and reduced guanylate cyclase activity of myocytes was associated with the statistically significant increase of endothelium-independent vasodilatation.