MUG: A mutation overview of GPCR subfamily A17 receptors

Abstract

G protein-coupled receptors (GPCRs) mediate several signaling pathways through a general mechanism that involves their activation, upholding a chain of events that lead to the release of molecules responsible for cytoplasmic action and further regulation. These physiological functions can be severely altered by mutations in GPCR genes. GPCRs subfamily A17 (dopamine, serotonin, adrenergic and trace amine receptors) are directly related with neurodegenerative diseases, and as such it is crucial to explore known mutations on these systems and their impact in structure and function. A comprehensive and detailed computational framework - MUG (Mutations Understanding GPCRs) - was constructed, illustrating key reported mutations and their effect on receptors of the subfamily A17 of GPCRs. We explored the type of mutations occurring overall and in the different families of subfamily A17, as well their localization within the receptor and potential effects on receptor functionality. The mutated residues were further analyzed considering their pathogenicity. The results reveal a high diversity of mutations in the GPCR subfamily A17 structures, drawing attention to the considerable number of mutations in conserved residues and domains. Mutated residues were typically hydrophobic residues enriched at the ligand binding pocket and known activating microdomains, which may lead to disruption of receptor function. MUG as an interactive web application is available for the management and visualization of this dataset. We expect that this interactive database helps the exploration of GPCR mutations, their influence, and their familywise and receptor-specific effects, constituting the first step in elucidating their structures and molecules at the atomic level.

Keywords: Database; ECL, extracellular loop; FDA, Food and Drug Administration; G protein-coupled receptors; GEFs, GTP-exchange factors; GOF, gain-of-function; GPCR subfamily A17; GPCRs, G protein-coupled receptors; ICL, intracellular loop; LOF, loss-of-function; MUG, mutations understanding GPCRs; Natural variants; Neurodegenerative diseases; TM, transmembrane.

Graphical abstract

Fig. 1

Structural visualization of the inactive D₁R in a schematic lipid membrane. Close-ups were used to identify and locate relevant residues, including ligand binding site, allosteric binding site, known activating microdomains (DRY, PIF, CWxP, and NPxxY), key cysteines, GPCR-G protein interacting site, GPCR-Arrestin interacting site and other residues. Ligand binding site, GPCR-G protein and GPCR-Arrestin interacting sites were indicated by green arrows. Allosteric binding site was indicated by a solid red surface.

Fig. 2

General analysis of mutation frequency over the GPCR subfamily A17 database. A. Total number of mutations in each receptor. B. Number of mutations sorted by type.

Fig. 3

Distribution of the different mutations in topological domains of each family (dopamine, serotonin, adrenergic and trace amine receptors). The number of variants per topological domain as defined by the GPCR subfamily A17 molecular architecture of N- and C-terminal regions, seven TM helices (TM1 to 7), three extracellular loops (ECL1 to 3) and three intracellular loops (ICL1 to 3).

Fig. 4

Missense mutations for all 25 receptors of GPCR subfamily A17 in the database. (A) Missense mutations per group of amino acids (hydrophobic, polar, negative charge and positive charge) and (B) per amino acid.

Fig. 5

Pie chart showing the proportion of mutations found for each relevant area for all the members of subfamily A17.

Fig. 6

Percentage of homozygous vs heterozygous missense mutations in each relevant residues group. Groups of relevant residues include ligand binding site, allosteric binding site, G protein binding site, arrestin binding site, microdomains, cysteines, and other residues.