title: The phytosulfokine (PSK) receptor is capable of guanylate cyclase activity and enabling cyclic GMP-dependent signaling in plants.
abstract: Phytosulfokines (PSKs) are sulfated pentapeptides that stimulate plant growth and differentiation mediated by the PSK receptor (PSKR1), which is a leucine-rich repeat receptor-like kinase. We identified a putative guanylate cyclase (GC) catalytic center in PSKR1 that is embedded within the kinase domain and hypothesized that the GC works in conjunction with the kinase in downstream PSK signaling. We expressed the recombinant complete kinase (cytoplasmic) domain of AtPSKR1 and show that it has serine/threonine kinase activity using the Ser/Thr peptide 1 as a substrate with an approximate K(m) of 7.5 μm and V(max) of 1800 nmol min(-1) mg(-1) of protein. This same recombinant protein also has GC activity in vitro that is dependent on the presence of either Mg(2+) or Mn(2+). Overexpression of the full-length AtPSKR1 receptor in Arabidopsis leaf protoplasts raised the endogenous basal cGMP levels over 20-fold, indicating that the receptor has GC activity in vivo. In addition, PSK-α itself, but not the non-sulfated backbone, induces rapid increases in cGMP levels in protoplasts. Together these results indicate that the PSKR1 contains dual GC and kinase catalytic activities that operate in vivo and that this receptor constitutes a novel class of enzymes with overlapping catalytic domains.
authors.affiliation: Medicinal Chemistry and Drug Action, Monash Institute of Pharmaceutical Sciences, Monash University (Parkville campus), 381 Royal Parade, Parkville, Victoria 3052, Australia.
authors.forename: Lusisizwe
authors.initials: L
authors.lastname: Kwezi
authors.forename: Oziniel
authors.initials: O
authors.lastname: Ruzvidzo
authors.forename: Janet I
authors.initials: JI
authors.lastname: Wheeler
authors.forename: Kershini
authors.initials: K
authors.lastname: Govender
authors.forename: Sylvana
authors.initials: S
authors.lastname: Iacuone
authors.forename: Philip E
authors.initials: PE
authors.lastname: Thompson
authors.forename: Chris
authors.initials: C
authors.lastname: Gehring
authors.forename: Helen R
authors.initials: HR
authors.lastname: Irving
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000166:cytology* / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020134:Catalytic Domain; D006152:Cyclic GMP / Q000096:biosynthesis / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D006162:Guanylate Cyclase / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D010770:Phosphotransferases / Q000378:metabolism; D011523:Protoplasts / Q000201:enzymology / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D029681:Arabidopsis Proteins; C515018:PSKR1 protein, Arabidopsis; D011956:Receptors, Cell Surface; D010770:Phosphotransferases; D006162:Guanylate Cyclase; D006152:Cyclic GMP