Project Abstract Atrial natriuretic peptide (ANP) plays a pivotal role in cardiovascular homeostasis, produced by cardiomyocytes as a response to conditions like hypervolemia and hypertension. Its wide array of beneficial effects, including vasodilation, increased natriuresis, diuresis, and its anti-fibrotic and anti-hypertrophic actions within the heart, underscore its physiological importance. These effects are mediated through the atrial natriuretic peptide receptor (ANPR), also known as GC-A. This receptor uniquely integrates the recognition of peptide hormones and the generation of the second messenger cGMP within a single polypeptide chain. The deletion of either ANP or GC-A genes in mice results in elevated blood pressure and a cascade of renal, vascular, and cardiac dysfunctions, culminating in hypertensive heart disease. These findings, corroborated by both mouse genetic studies and the clinical utility of natriuretic peptides, highlight the critical regulatory role of ANP in maintaining cardiovascular equilibrium. Despite this, a comprehensive understanding of the structural mechanisms governing GC-A regulation remains elusive. This proposal is structured around three primary objectives, each aimed at unraveling different aspects of GC-A's structural and functional regulation. Aim 1: Structural basis of GC-A activation by ANP. We intend to delineate the structural changes occurring within GC-A upon ANP binding. This involves elucidating how ANP interaction with the extracellular domain triggers conformational adjustments leading to cGMP production. Aim 2: Regulation by the kinase-homology domain (KHD). The KHD of GC-A is implicated in receptor activity regulation, yet its precise functional role remains to be defined. This aim focuses on understanding how ATP binding to the KHD influences GC-A's activation by ANP. Through structural, biochemical, and functional studies, we will explore the KHD's contribution to receptor regulation and its impact on the receptor's overall activity. Aim 3: Mechanism of cyclase catalytic activity regulation. Despite GC-A's homodimeric structure, suggesting the presence of two catalytic sites, there is ongoing debate about their functional status during receptor activation. This aim seeks to clarify whether one or both catalytic sites are operational and to understand the conformational dynamics that enable GTP conversion to cGMP. Our proposed research is poised to significantly advance our understanding of GC-A's structure-function relationship and its regulatory mechanisms. The implications of this work extend beyond basic science, offering potential strategies for the development of targeted therapeutic interventions to modulate GC-A activity in cardiovascular diseases.

Atrial natriuretic peptide (ANP) is a critical peptide hormone produced by the heart in response to cardiovascular stress, acting to lower blood pressure and maintain vascular homeostasis. Its effects are mediated through a specific receptor, ANP receptor (GC-A), which triggers a cascade leading to vasodilation and reduced blood volume. Investigating the structural mechanisms and regulatory pathways of the ANP receptor not only enhances our scientific understanding but also holds significant implications for developing targeted therapies for hypertension and cardiovascular diseases, directly impacting public health.