Mechanism of Hormone Peptide Activation of a GPCR: Angiotensin II Activated State of AT1R Initiated by van der Waals Attraction.

ABSTRACT

We present a succession of structural changes involved in hormone peptide activation of a prototypical GPCR. Microsecond molecular dynamics simulation generated conformational ensembles reveal propagation of structural changes through key "microswitches" within human AT1R bound to native hormone. The endocrine octa-peptide angiotensin II (AngII) activates AT1R signaling in our bodies which maintains physiological blood pressure, electrolyte balance, and cardiovascular homeostasis. Excessive AT1R activation is associated with pathogenesis of hypertension and cardiovascular diseases which are treated by sartan drugs. The mechanism of AT1R inhibition by sartans has been elucidated by 2.8 Å X-ray structures, mutagenesis, and computational analyses. Yet, the mechanism of AT1R activation by AngII is unclear. The current study delineates an activation scheme initiated by AngII binding. A van der Waals "grasp" interaction between Phe8AngII with Ile2887.39 in AT1R induced mechanical strain pulling Tyr2927.43 and breakage of critical interhelical H-bonds, first between Tyr2927.43 and Val1083.32 and second between Asn1113.35 and Asn2957.46. Subsequently changes are observed in conserved microswitches DRYTM3, Yx7K(R)TM5, CWxPTM6, and NPxxYTM7 in AT1R. Activating the microswitches in the intracellular region of AT1R may trigger formation of the G-protein binding pocket as well as exposure of helix-8 to cytoplasm. Thus, the active-like conformation of AT1R is initiated by the van der Waals interaction of Phe8AngII with Ile2887.39, followed by systematic reorganization of critical interhelical H-bonds and activation of microswitches.