GPCR-bigrams: Enigmatic signaling components in oomycetes
In each model, agonist binding on the receptor domain leads to downstream responses. In (A), the catalytic domain (c) is directly activated, leading to conversion of a substrate (s) to a product (p). In (B), proteolytic cleavage (purple) yields a mature GPCR and an active catalytic domain. In (C), G-proteins are activated, which either directly or indirectly activate the catalytic domain. In (D), the catalytic domain is activated by G-proteins or effector proteins, activated by a canonical GPCR. In (E), the catalytic domain is inactive (grey), and instead, G-proteins are activated to induce the production of second messengers. In (F), the receptor displays biased agonism and either activates G-proteins (left) or the catalytic domain (right). In (G), phosphorylation of the GPCR (yellow circles) by kinase activity of GPCR-TKLs leads to recruitment of β-arrestin, thereby either blocking signaling via G-proteins (left) or scaffolding effector proteins to initiate downstream signaling (right). GPCR, G-protein coupled receptor; TKL, tyrosine kinase-like.