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Journal of Molecular BiologyBioengineeringPeer-reviewed journal article

GPCRchimeraDB: A database of chimeric G protein-coupled receptors (GPCRs) to assist their design

Charlotte CrauwelsiD, Adrián DíaziD, Wim VrankeniD

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Abstract

G protein-coupled receptors (GPCRs) are membrane proteins crucial to numerous diseases, yet many remain poorly characterized and untargeted by drugs. Chimeric GPCRs have emerged as valuable tools for elucidating GPCR function by facilitating the identification of signaling pathways, resolving structures, and discovering novel ligands of poorly understood GPCRs. Such chimeric GPCRs are obtained by merging a well- and less-well-characterized GPCR at the intracellular limits of their transmembrane regions or intracellular loops, leveraging knowledge transfer from the well-characterized GPCR. However, despite the 212 chimeric GPCRs engineered to date, the design process remains largely trial-and-error and lacks a standardized approach. To address this gap, we introduce GPCRchimeraDB (https://www.bio2byte.be/gpcrchimeradb/), the first comprehensive database dedicated to chimeric GPCRs. It catalogs 212 chimeric receptors, identified through literature review, and includes 1,755 class A natural GPCRs, enabling connections between chimeras and their parent receptors while facilitating the exploration of novel parent combinations. Both chimeric and natural GPCR entries are extensively described at the sequence, structural, and biophysical level through a range of visualization tools, with annotations from resources like UniProt and GPCRdb and predictions from AlphaFold2 and b2btools. Additionally, GPCRchimeraDB offers a GPCR sequence aligner and a feature comparator to investigate differences between natural and chimeric receptors. It also provides design guidelines to support rational chimera engineering. GPCRchimeraDB is therefore a resource to facilitate and optimize the design of new chimeras, so helping to gain insights into poorly characterized receptors and contributing to advances in GPCR therapeutic development.

In-depth summary

Claude Sonnet 4.6 · xhigh effort · 7 Nov 2026 · from the full text of version 3 (17 Apr 2025) · CC BY 4.0

Resource of 212 literature-curated chimeric class A GPCRs linked to 1,755 natural class A mammalian GPCRs, annotated at sequence, structure and biophysics level, with guidelines for designing new chimeras.

The paper states that no generic approach to designing chimeric GPCRs exists, perhaps because earlier designs lacked an overview and annotations. GPCRchimeraDB is presented as the first resource to standardize and consolidate chimeric GPCR data, extending the descriptions in GPCRdb.

Key results

  1. ShownLiterature curation found 212 chimeric GPCRs, which the authors sort into three design types by strategy and purpose: Type 1 (opsin-based), Type 2 (non-sensory EC parent) and Type 3 (well-characterized IC parent with a known stabilizing nanobody).

    Type 1: 94 designs, largely rhodopsin-based. Type 2: 103 designs in 30 papers with 42 unique parent combinations. Type 3: 15 designs, all with human kappa opioid receptor (KOR) at the IC side, stabilized by nanobody Nb6. · Classifying chimeras in GPCRchimeraDB; Previously designed chimeras in GPCRchimeraDB

  2. ShownEach of the 1,755 natural class A mammalian GPCRs and 212 chimeras gets a standardized entry, with a naming convention for chimeras. Entries are linked to their parents and to an interactive 1D-3D sequence-structure viewer. Chimeras have fewer annotations than natural receptors.

    Natural entries draw on UniProt, GPCRdb, PDB, AFDB and Scop3P, plus b2btools and DSSP predictions. Chimeras get predicted AF2, AlphaFold2 multistate (AFms) and ESMFold models, and biophysical differences from their parents. UniProt, GPCRdb and Scop3P mutation and PTM data are not available for chimeras. · General features; Biophysical profile; Extensive description of chimeric and natural…

  3. SuggestedA comparison of predicted models against experimental chimera structures could not identify the best predictor. AF2 single-sequence mode gave highly inaccurate models for chimeras.

    Ten experimental chimera structures (7 Type 3 designs) were compared with AF2, ESMFold and AFms models; RMSD differences were small and variable. All had one swapped region (end of TM5 to start of TM6), the same IC parent (KOR) and 6 EC parents. · Extensive description of chimeric and natural…

  4. ClaimedThe paper gives a five-step workflow and four rules for choosing cutting sites when designing a chimera: keep the EC parent's microswitches, keep secondary structure, favor EC parent sequence, and keep the IC parent's G protein-binding residues.

    Rules are drawn from the studied literature. They are supported by database features (motifs, secondary structure, interacting residues, parent-versus-chimera conservation and biophysical tracks). No newly designed chimera is tested in this paper. · Leveraging GPCRchimeraDB: How to design a novel…; 3. Respect the key rules for determining cutting…; 4. Improve the cutting point selection by…; 5. Design the chimera

  5. ShownChimera functionality values cannot be compared across entries. The database stores whatever quantitative or yes/no value each paper reported, and does not report how many chimeras succeeded.

    Assays (real-time versus endpoint), conditions and result presentation (relative versus absolute) differ between publications. The authors note likely publication bias toward well-expressing, functional chimeras. · Collecting natural and chimeric GPCRs; Previously designed chimeras in GPCRchimeraDB

Methods, data and reproducibility

Chimeras were collected by systematic literature search plus a BLAST search of the PDB for chimeric chains. Parents, cutting sites and sequences were extracted with an in-house Python pipeline, and entries were annotated from public databases and sequence/structure predictors, then served through a Django and React web application.

  • Chimeric class A GPCRs curated from the literature (design types 1, 2 and 3) · multiple mammalian species (examples in text: bovine, human, rat) · n = 212 chimeras · 10.5281/zenodo.14989364
  • Natural reviewed class A (rhodopsin-like) mammalian GPCRs from InterPro, filtered to those with 7 predicted TM helices · multiple mammalian species · n = 1,755 entries · IPR017452
  • Experimental 3D structures of chimeric GPCRs used to compare AF2, ESMFold and AFms models · n = 10 structures (7 Type 3 designs)
Methods & tools
BLAST, Biopython, UniProt, GPCRdb, AlphaFold2, AlphaFold2 multistate, ESMFold, b2btools, DSSP, HMMER, SIMSApiper, CD-HIT and IQ-TREE
Software & environment
Server runs Ubuntu 22.04; backend in Python 3 with Django and SQLite3, frontend in React.js, uWSGI and NGINX. No package versions are stated.
Reproducibility gaps
Zenodo deposit is given as a DOI only (10.5281/zenodo.14989364), and no software versions are listed for the annotation pipeline.
Limitations (5)
  • Functionality values are not normalized across entries because assays and conditions differ, and published chimeras likely over-represent functional, well-expressing designs. · stated by the authors
  • The structure-prediction comparison is inconclusive: few structures, all with one swapped region, the same IC parent (KOR) and only 6 EC parents, so no best predictor can be named. · stated by the authors
  • Version 1 covers only class A GPCRs with chimeras built by swapping IC TM boundaries and IC loops. Chimeras with exchanged EC loops or TMs, non-class A parents and interclass chimeras are excluded. · stated by the authors
  • AFms models exist only for chimeras and human natural GPCRs, and chimeras lack mutation and PTM annotations available for natural receptors. · stated by the authors
  • The design rules and workflow come from literature review and are not validated here by designing or testing new chimeras. · noted in this summary

Read this if you plan to design a chimeric class A GPCR and want past designs, cutting sites, parent annotations and biophysical profiles in one place.

Citations
2
FWCI
0.59
Field percentile
top 42%

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