TY - JOUR
T1 - A sweet cycle for Arabidopsis G-proteins
T2 - Recent discoveries and controversies in plant G-protein signal transduction
AU - Johnston, Christopher A.
AU - Willard, Melinda D.
AU - Kimple, Adam J.
AU - Siderovski, David P.
AU - Willard, Francis S.
N1 - Funding Information:
Work in the Siderovski laboratory on Arabidopsis G-protein signaling is supported by National Institute of General Medical Sciences R01 GM082892 (to D.P.S.).
PY - 2008/12
Y1 - 2008/12
N2 - Heterotrimeric G-proteins are a class of signal transduction proteins highly conserved throughout evolution that serve as dynamic molecular switches regulating the intracellular communication initiated by extracellular signals including sensory information. This property is achieved by a guanine nucleotide cycle wherein the inactive, signaling-incompetent Gα subunit is normally bound to GDP; activation to signaling-competent Gα occurs through the exchange of GDP for GTP (typically catalyzed via seven-transmembrane domain G-protein coupled receptors [GPCRs]), which dissociates the Gβγ dimer from Gα·GTP and initiates signal transduction. The hydrolysis of GTP, greatly accelerated by "Regulator of G-protein Signaling" (RGS) proteins, returns Gα to its inactive GDP-bound form and terminates signaling. Through extensive characterization of mammalian Gα isoforms, the rate-limiting step in this cycle is currently considered to be the GDP/GTP exchange rate, which can be orders of magnitude slower than the GTP hydrolysis rate. However, we have recently demonstrated that, in Arabidopsis, the guanine nucleotide cycle appears to be limited by the rate of GTP hydrolysis rather than nucleotide exchange. This finding has important implications for the mechanism of sugar sensing in Arabidopsis. We also discuss these data on Arabidopsis G-protein nucleotide cycling in relation to recent reports of putative plant GPCRs and heterotrimeric G-protein effectors in Arabidopsis.
AB - Heterotrimeric G-proteins are a class of signal transduction proteins highly conserved throughout evolution that serve as dynamic molecular switches regulating the intracellular communication initiated by extracellular signals including sensory information. This property is achieved by a guanine nucleotide cycle wherein the inactive, signaling-incompetent Gα subunit is normally bound to GDP; activation to signaling-competent Gα occurs through the exchange of GDP for GTP (typically catalyzed via seven-transmembrane domain G-protein coupled receptors [GPCRs]), which dissociates the Gβγ dimer from Gα·GTP and initiates signal transduction. The hydrolysis of GTP, greatly accelerated by "Regulator of G-protein Signaling" (RGS) proteins, returns Gα to its inactive GDP-bound form and terminates signaling. Through extensive characterization of mammalian Gα isoforms, the rate-limiting step in this cycle is currently considered to be the GDP/GTP exchange rate, which can be orders of magnitude slower than the GTP hydrolysis rate. However, we have recently demonstrated that, in Arabidopsis, the guanine nucleotide cycle appears to be limited by the rate of GTP hydrolysis rather than nucleotide exchange. This finding has important implications for the mechanism of sugar sensing in Arabidopsis. We also discuss these data on Arabidopsis G-protein nucleotide cycling in relation to recent reports of putative plant GPCRs and heterotrimeric G-protein effectors in Arabidopsis.
KW - Arabidopsis
KW - G-protein
KW - Glucose
KW - Nucleotide exchange
KW - RGS protein
UR - http://www.scopus.com/inward/record.url?scp=57749110450&partnerID=8YFLogxK
U2 - 10.4161/psb.3.12.7184
DO - 10.4161/psb.3.12.7184
M3 - Review article
C2 - 19513240
AN - SCOPUS:57749110450
SN - 1559-2316
VL - 3
SP - 1067
EP - 1076
JO - Plant Signaling and Behavior
JF - Plant Signaling and Behavior
IS - 12
ER -