Rare variant in intracellular loop-2 of the ghrelin receptor reveals novel mechanisms of GPCR biased signaling and trafficking
Bibliographic record
Abstract
ABSTRACT G protein-coupled receptors (GPCRs) are the largest class of integral membrane proteins and the most common pharmaceutical drug target. Through allosteric coupling, GPCRs transduce extracellular stimuli into physiologically-relevant intracellular signaling cascades via G proteins and β-arrestin (βarr). The growth hormone secretagogue receptor (GHSR) is a rhodopsin-like, peptide hormone GPCR considered a promising target for both metabolic and neurological diseases. Here, by characterizing an ultra-rare coding variant in intracellular loop-2 (ICL2) of the GHSR, GHSR L149P (L149P), we establish a unique role of ICL2 in GPCR biased signaling, lipid modulation, and intracellular trafficking. Using an array of bioluminescence resonance energy transfer (BRET)-based assays, we show that the natural L149P mutant exhibits (i) a constitutive plasma membrane [PM] expression bias, (ii) preferential partitioning away from cholesterol-enriched PM microdomains, (iii) enhanced agonist-directed endocytosis, and (iv) dramatic signaling bias towards βarr1/2 over Gα q , Gα i/o , and Gα 12/13 . Using a combination of pharmacological and genetic tools, we demonstrate that βarr1/2 recruitment to L149P requires G protein-coupled receptor kinase-2/3 (GRK2/3)-mediated phosphorylation, but it does not utilize protein kinase C (PKC), Gβγ-dependent GRK2/3 translocation, or Gα i/o , supporting a G protein-independent mechanism. Lastly, we found that βarr1/2 recruitment to L149P requires both GRK2/3 and GRK5/6, while the wild-type GHSR relies exclusively on GRK2/3, consistent with increased GRK6 pre-coupling to the L149P mutant. Collectively, our findings using a rare, natural variant reveal novel mechanisms of GPCR regulation that could be leveraged to improve personalized medicine and facilitate the rational design/discovery of GPCR ICL2 -directed drugs. SIGNIFICANCE STATEMENT G protein-coupled receptors (GPCRs) are the largest class of membrane proteins and the most prevalent drug target class in medicine. However, the structural and mechanistic determinants of GPCR signaling and membrane compartmentalization remains incompletely understood. Here, we characterize an ultra-rare natural variant of the growth hormone secretagogue receptor (GHSR), L149P, that uncovers an unanticipated role for intracellular loop 2 (ICL2) in receptor biased signaling, intracellular trafficking, and membrane lipid modulation. The variant exhibits a strong bias for β-arrestin signaling independent of canonical G protein pathways, mediated instead by unique GPCR kinase interactions and a distinct subcellular distribution. These findings reveal previously unrecognized regulatory layers in GPCR structure/function and identify ICL2 as a promising target for designing precision pharmacotherapeutics.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".