Abstract
Computational prediction and in vivo protein coupling experiments identify candidate plant G-protein coupled receptors in Arabidopsis, rice and poplar.
Highlights
The classic paradigm of heterotrimeric G-protein signaling describes a heptahelical, membrane-spanning G-protein coupled receptor that physically interacts with an intracellular Gα subunit of the G-protein heterotrimer to transduce signals
Because Gprotein coupled receptor (GPCR) sequence conservation even within a single GPCR family of an organism can be lower than 25% [1], GPCRs are identified not by sequence homology but rather by their ability to couple with an intracellular heterotrimeric G-protein α subunit and by their two-dimensional topology, which classically consists of an extracellular amino terminus, seven membrane spanning domains connected by three intracellular and three extracellular loops, and an intracellularly located carboxy-terminal tail
Because the quasi-periodic feature classifier (QFC) algorithm was reported to have an approximately 98% success rate in classifying GPCRs from non-GPCRs [44], and GPCRs are classically described by their 7TM topology, our criterion to identify a protein sequence as a candidate GPCR comprises the requirements of direct prediction as a GPCR by the QFC algorithm and the presence of exactly seven TM domains as predicted by at least two of the three TM prediction programs used (TMHMM2, HMMMTOP2, and Phobius) after correction for signal peptide misprediction (Figure 1)
Summary
The classic paradigm of heterotrimeric G-protein signaling describes a heptahelical, membrane-spanning G-protein coupled receptor that physically interacts with an intracellular Gα subunit of the G-protein heterotrimer to transduce signals. The heterotrimeric G-protein signaling mechanism is conserved across metazoa, and readily identifiable in plants, but the low sequence conservation of G-protein coupled receptors hampers the identification of novel ones. One of the primary sensing mechanisms used by metazoans involves Gprotein coupled receptor (GPCR) signaling cascades. These cascades are composed of, at the most simplistic level, a plasma membrane localized stimulus-sensing GPCR that transduces the extracellular signal to an intracellular heterotrimeric G-protein complex, thereby activating downstream signaling cascades. Gα and the βγ dimer proceed to initiate downstream signaling cascades [2,3]
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