LPA1 extracellular loop residues 115 and 191 are not required for receptor activation but prevent Ki16425 super-antagonism

Abstract

Lysophosphatidic acid receptor 1 (LPA₁) is a clinically important target, which confers a biological response to lysophosphatidic acid-type agonists. Recently, the 3D structure of LPA₁ resolved using X-ray crystallography and our site-directed mutagenesis has provided significant insight into the mechanism of LPA₁ activation and antagonism. In the present study, we report that extracellular loop residues (R115 and D191) are not required for receptor activation but repress Ki16425-type super-antagonism but not LPA-analogue antagonists using a combination of site-directed mutagenesis and intracellular calcium assay procedures. The underlying mechanism was further queried using an all-atom molecular dynamics (MD) simulation. The result showed that Ki16425 when bound to LPA₁ evolved characteristic conformational and optimal route communication signatures as a LPA (C18:1)-agonist which is reversed in R115A and D191A mutants. In conclusion, Ki16425 is a super-antagonist when bound to mutant (R115A and D191A) LPA₁.