Activation induces structural changes in the liganded angiotensin II type 1 receptor

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• The angiotensin II type 1 receptor (hAT(1)) is a G protein-coupled receptor activated by angiotensin II.
• Mechanisms of hAT(1) activation remain experimentally unvalidated.
• Previous studies identified ligand contacts in transmembrane domains (TMD) III, VI, and VII.

Purpose of the Study:

• To experimentally validate activation mechanisms of the hAT(1) receptor.
• To identify novel ligand-receptor contacts in TMD I, II, IV, and V.
• To elucidate structural rearrangements between inactive and active hAT(1) conformations.

Main Methods:

• Construction and analysis of 53 individual methionine mutants in TMD I, II, IV, and V of both wild-type (WT) and constitutively active N111G-hAT(1) receptors.
• Photolabeling with a neutral antagonist followed by cyanogen bromide digestion to identify ligand-receptor proximity.
• Homology modeling and restrained molecular dynamics to analyze structural changes.

Main Results:

• Identified two novel ligand contact points: Phe-77 in TMD II and Asn-200 in TMD V, specifically in the constitutively active mutant.
• These are the first reported direct ligand contacts with TMD II and V of hAT(1).
• Structural modeling revealed significant TMD rearrangements between the basal (WT) and activated (N111G) receptor forms.

Conclusions:

• The study provides the first experimental evidence of direct ligand contacts with TMD II and V of the hAT(1) receptor.
• The identified contact points and subsequent modeling illuminate the structural basis of hAT(1) activation.
• Findings contribute to a deeper understanding of G protein-coupled receptor activation mechanisms.