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. 2019 Oct 31;179(4):895–908.e21. doi: 10.1016/j.cell.2019.10.010

Figure 1.

Figure 1

The Human G Protein-Coupled Receptor-Ligand System

(A) GPCRs represent the predominant targets for endogenous ligands. Peptides are more numerous, larger and bind with higher affinity than non-peptide ligands. From the top: (1) distinct endogenous ligands by target family; (2) endogenous GPCR ligands, of which “principal” ligands are considered most physiologically relevant; (3) peptide and small-molecule binding receptors, of which “paired” ones have a known principal endogenous ligand; and (4) ligands per receptor and vice versa (averages).

(B and C) Ligand molecular weight distribution (B) and cognate receptor affinity (C) (boxplots show a median and interquartile range of 1.5; Wilcoxon rank-sum test, p < 1 × 10−5). Data are from the Guide to Pharmacology database (Harding et al., 2018).

(D) GPCR-ligand systems vary in complexity from 1:1 to many:many (gray circles show numbers of each system; data are shown in Table S1).

See also Figure S2.