Single amino acid residue-linked signaling shifts in the transduction activities of atrial and type C natriuretic factor receptor guanylate cyclases

Multilimbed membrane guanylate cyclase signaling system, evolutionary ladder

One monumental discovery in the field of cell biology is the establishment of the membrane guanylate cyclase signal transduction system. Decoding its fundamental, molecular, biochemical, and genetic features revolutionized the processes of developing therapies for diseases of endocrinology, cardio-vasculature, and sensory neurons; lastly, it has started to leave its imprints with the atmospheric carbon dioxide. The membrane guanylate cyclase does so via its multi-limbed structure. The inter-netted limbs throughout the central, sympathetic, and parasympathetic systems perform these functions. They generate their common second messenger, cyclic GMP to affect the physiology. This review describes an historical account of their sequential evolutionary development, their structural components and their mechanisms of interaction. The foundational principles were laid down by the discovery of its first limb, the ACTH modulated signaling pathway (the companion monograph). It challenged two general existing dogmas at the time. First, there was the question of the existence of a membrane guanylate cyclase independent from a soluble form that was heme-regulated. Second, the sole known cyclic AMP three-component-transduction system was modulated by GTP-binding proteins, so there was the question of whether a one-component transduction system could exclusively modulate cyclic GMP in response to the polypeptide hormone, ACTH. The present review moves past the first question and narrates the evolution and complexity of the cyclic GMP signaling pathway. Besides ACTH, there are at least five additional limbs. Each embodies a unique modular design to perform a specific physiological function; exemplified by ATP binding and phosphorylation, Ca²⁺-sensor proteins that either increase or decrease cyclic GMP synthesis, co-expression of antithetical Ca²⁺ sensors, GCAP1 and S100B, and modulation by atmospheric carbon dioxide and temperature. The complexity provided by these various manners of operation enables membrane guanylate cyclase to conduct diverse functions, exemplified by the control over cardiovasculature, sensory neurons and, endocrine systems.

Integrative Signaling Networks of Membrane Guanylate Cyclases: Biochemistry and Physiology

This monograph presents a historical perspective of cornerstone developments on the biochemistry and physiology of mammalian membrane guanylate cyclases (MGCs), highlighting contributions made by the authors and their collaborators. Upon resolution of early contentious studies, cyclic GMP emerged alongside cyclic AMP, as an important intracellular second messenger for hormonal signaling. However, the two signaling pathways differ in significant ways. In the cyclic AMP pathway, hormone binding to a G protein coupled receptor leads to stimulation or inhibition of an adenylate cyclase, whereas the cyclic GMP pathway dispenses with intermediaries; hormone binds to an MGC to affect its activity. Although the cyclic GMP pathway is direct, it is by no means simple. The modular design of the molecule incorporates regulation by ATP binding and phosphorylation. MGCs can form complexes with Ca²⁺-sensing subunits that either increase or decrease cyclic GMP synthesis, depending on subunit identity. In some systems, co-expression of two Ca²⁺ sensors, GCAP1 and S100B with ROS-GC1 confers bimodal signaling marked by increases in cyclic GMP synthesis when intracellular Ca²⁺ concentration rises or falls. Some MGCs monitor or are modulated by carbon dioxide via its conversion to bicarbonate. One MGC even functions as a thermosensor as well as a chemosensor; activity reaches a maximum with a mild drop in temperature. The complexity afforded by these multiple limbs of operation enables MGC networks to perform transductions traditionally reserved for G protein coupled receptors and Transient Receptor Potential (TRP) ion channels and to serve a diverse array of functions, including control over cardiac vasculature, smooth muscle relaxation, blood pressure regulation, cellular growth, sensory transductions, neural plasticity and memory.

Molecular classification of an elasmobranch angiotensin receptor: quantification of angiotensin receptor and natriuretic peptide receptor mRNAs in saltwater and freshwater populations of the Atlantic stingray

Among the most conserved osmoregulatory hormone systems in vertebrates are the renin-angiotensin system (RAS) and the natriuretic peptides (NPs). We examined the RAS and NP system in the euryhaline Atlantic stingray, Dasyatis sabina (Lesueur). To determine the relative sensitivity of target organs to these hormonal systems, we isolated cDNA sequences encoding the D. sabina angiotensin receptor (AT) and natriuretic peptide type-B receptor (NPR-B). We then determined the tissue-specific expression of their mRNAs in saltwater D. sabina from local Texas waters and an isolated freshwater population in Lake Monroe, Florida. AT mRNA was most abundant in interrenal tissue from both populations. NPR-B mRNA was most abundant in rectal gland tissue from both populations, and also highly abundant in the kidney of saltwater D. sabina. This study is the first to report the sequence of an elasmobranch angiotensin receptor, and phylogenetic analysis indicates that the D. sabina receptor is more similar to AT(1) vs. AT(2) proteins. This classification is further supported by molecular analysis of AT(1) and AT(2) proteins demonstrating conservation of AT(1)-specific amino acid residues and motifs in D. sabina AT. Molecular classification of the elasmobranch angiotensin receptor as an AT(1)-like protein provides fundamental insight into the evolution of the vertebrate RAS.

Membrane guanylate cyclase is a beautiful signal transduction machine: overview

This article is a sequel to the four earlier comprehensive reviews which covered the field of membrane guanylate cyclase from its origin to the year 2002 (Sharma in Mol Cell Biochem 230:3-30, 2002) and then to the year 2004 (Duda et al. in Peptides 26:969-984, 2005); and of the Ca(2+)-modulated membrane guanylate cyclase to the year 1997 (Pugh et al. in Biosci Rep 17:429-473, 1997) and then to 2004 (Sharma et al. in Curr Top Biochem Res 6:111-144, 2004). This article contains three parts. The first part is "Historical"; it is brief, general, and freely borrowed from the earlier reviews, covering the field from its origin to the year 2004 (Sharma in Mol Cell Biochem, 230:3-30, 2002; Duda et al. in Peptides 26:969-984, 2005). The second part focuses on the "Ca(2+)-modulated ROS-GC membrane guanylate cyclase subfamily". It is divided into two sections. Section "Historical" and covers the area from its inception to the year 2004. It is also freely borrowed from an earlier review (Sharma et al. in Curr Top Biochem Res 6:111-144, 2004). Section "Ca(2+)-modulated ROS-GC membrane guanylate cyclase subfamily" covers the area from the year 2004 to May 2009. The objective is to focus on the chronological development, recognize major contributions of the original investigators, correct misplaced facts, and project on the future trend of the field of mammalian membrane guanylate cyclase. The third portion covers the present status and concludes with future directions in the field.

ATP-regulated module (ARM) of the atrial natriuretic factor receptor guanylate cyclase

ATP is an obligatory agent for the atrial natriuretic factor (ANF) and the type C natriuretic peptide (CNP) signaling of their respective receptor guanylate cyclases, ANF-RGC and CNP-RGC. Through a common mechanism, it binds to a defined ARM domain of the cyclase, activates the cyclase and transduces the signal into generation of the second messenger cyclic GMP. In this presentation, the authors review the ATP-regulated transduction mechanism and refine the previously simulated three-dimensional ARM model (Duda T, Yadav P, Jankowska A, Venkataraman V, Sharma RK. Three dimensional atomic model and experimental validation for the ATP-regulated module (ARM) of the atrial natriuretic factor receptor guanylate cyclase. Mol Cell Biochem 2000;214:7-14; reviewed in: Sharma RK, Yadav P, Duda T. Allosteric regulatory step and configuration of the ATP-binding pocket in atrial natriuretic factor receptor guanylate cyclase transduction mechanism. Can J Physiol Pharmacol 2001;79: 682-91; Sharma RK. Evolution of the membrane guanylate cyclase transduction system. Mol Cell Biochem 2002;230:3-30). The model depicts the ATP-binding dependent configurational changes in the ARM and supports the concept that in the first step, ATP partially activates the cyclase and primes it for the subsequent transduction steps, resulting in full activation of the cyclase.

A new paradigm for hormone recognition and allosteric receptor activation revealed from structural studies of NPR-C

The natriuretic peptide system of hormones and receptors poses an abundance of interesting biophysical questions regarding receptor structure, hormone recognition, and receptor activation. Functional and biochemical data have implicated a series of conformational changes as the mechanism by which NP receptor activation is achieved. We have explored the structural basis of hormone recognition by the NP clearance receptor, termed NPR-C. While NPR-C does not contain the classical guanylyl-cyclase activity in its intracellular domains, its extracellular domain is highly similar to the GC-coupled members of this family. The 1:2 stoichiometry of hormone binding to NPR-C is also used by NPR-A and -B to bind hormones. The structure of NPR-C in both quiescent and hormone-bound forms reveals the hormone intercalates within the interface of a receptor dimer, inducing a large-scale conformational change in the membrane proximal regions. This mechanism of hormone recognition will be conserved across the entire NPR family. The allosteric response of the NPR-C ectodomain to ligand binding is likely a glimpse of the general activation signal of these receptors, despite their differing downstream signaling cascades. In this review, we discuss our results on NPR-C and their relevance to the NPR family as a whole, as well as its place as a basic new paradigm for receptor activation.

Allosteric activation of a spring-loaded natriuretic peptide receptor dimer by hormone

Natriuretic peptides (NPs) are vasoactive cyclic-peptide hormones important in blood pressure regulation through interaction with natriuretic cell-surface receptors. We report the hormone-binding thermodynamics and crystal structures at 2.9 and 2.0 angstroms, respectively, of the extracellular domain of the unliganded human NP receptor (NPR-C) and its complex with CNP, a 22-amino acid NP. A single CNP molecule is bound in the interface of an NPR-C dimer, resulting in asymmetric interactions between the hormone and the symmetrically related receptors. Hormone binding induces a 20 angstrom closure between the membrane-proximal domains of the dimer. In each monomer, the opening of an interdomain cleft, which is tethered together by a linker peptide acting as a molecular spring, is likely a conserved allosteric trigger for intracellular signaling by the natriuretic receptor family.

Structural insights into the ligand binding domains of membrane bound guanylyl cyclases and natriuretic peptide receptors

Membrane bound guanylyl cyclases are single chain transmembrane receptors that produce the second messenger cGMP by either intra- or extracellular stimuli. This class of type I receptors contain an intracellular catalytic guanylyl cyclase domain, an adjacent kinase-like domain and an extracellular ligand binding domain though some receptors have their ligands yet to be identified. The most studied member is the atrial natriuretic peptide (ANP) receptor, which is involved in blood pressure regulation. Extracellular ANP binding induces a conformational change thereby activating the pre-oligomerized receptor leading to the production of cGMP. The recent crystal structure of the dimerized hormone binding domain of the ANP receptor provides a first three-dimensional view of this domain and can serve as a basis to structurally analyze mutagenesis, cross-linking, and genetic studies of this class of receptors as well as a non-catalytic homolog, the clearance receptor. The fold of the ligand binding domain is that of a bilobal periplasmic binding protein (PBP) very similar to that of the Leu/Ile/Val binding protein, AmiC, multi-domain transmembrane metabotropic glutamate receptors, and several DNA binding proteins such as the lactose repressor. Unlike these structural homologs, the guanylyl cyclase receptors bind much larger molecules at a site seemingly remote from the usual small molecule binding site in periplasmic binding protein folds. Detailed comparisons with these structural homologs offer insights into mechanisms of signal transduction and allosteric regulation, and into the remarkable usage of the periplasmic binding protein fold in multi-domain receptors/proteins.

Allosteric regulatory step and configuration of the ATP-binding pocket in atrial natriuretic factor receptor guanylate cyclase transduction mechanism

The atrial natriuretic factor (ANF) signal transduction mechanism consists of the transformation of the signal information into the production of cyclic GMP. The binding of ANF to its receptor, which is also a guanylate cyclase, generates the signal. This cyclase has been termed atrial natriuretic factor receptor guanylate cyclase, ANF-RGC. ANF-RGC is a single transmembrane-spanning protein. The ANF receptor domain resides in the extracellular region of the protein, and the catalytic domain is located in the intracellular region at the C-terminus of the protein. Thus, the signal is relayed progressively from the receptor domain to the catalytic domain, where it is converted into the formation of cyclic GMP. The first transduction step is the direct binding of ATP with ANF-RGC. This causes allosteric regulation of the enzyme and primes it for the activation of its catalytic moiety. The partial structural motif of the ATP binding domain in ANF-RGC has been elucidated, and it has been named ATP regulatory module (ARM). In this presentation, we provide a brief review of the ATP-regulated transduction mechanism and the ARM model. The model depicts a configuration of the ATP-binding pocket that has been experimentally validated, and the model shows that the ATP-dependent transduction process is a two- (or more) step event. The first step involves the binding of ATP with its ARM. This partially activates the cyclase and prepares it for the subsequent steps, which are consistent with its being phosphorylated and attaining the fully activated state.Key words: ANF, ANF-receptor guanylate cyclase (ANF-RGC), ATP, ATP-regulatory module (ARM).

Three dimensional atomic model and experimental validation for the ATP-Regulated Module (ARM) of the atrial natriuretic factor receptor guanylate cyclase

Atrial natriuretic factor (ANF) receptor guanylate cyclase (ANF-RGC) is a single chain transmembrane-spanning protein, containing both ANF binding and catalytic activities. ANF binding to the extracellular receptor domain activates the cytosolic catalytic domain, generating the second messenger cyclic GMP. Obligatory in this activation process is an intervening transduction step, which is regulated by the binding of ATP to the cyclase. The partial structural motif of the ATP binding domain of the cyclase has been elucidated and has been termed ATP Regulatory Module (ARM). The crystal structures of the tyrosine kinase domains of the human insulin receptor and haematopoietic cell kinase were used to derive a homology-based model of the ARM domain of ANF-RGC. The model identifies the precise configuration of the ATP-binding pocket in the ARM domain, accurately represents its ATP-dependent features, and shows that the ATP-dependent transduction phenomenon is a two-step mechanism. In the first step, ATP binds to its pocket and changes its configuration; in the second step, via an unknown protein kinase, it phosphorylates the cyclase for its full activation.

Three dimensional atomic model and experimental validation for the ATP-Regulated Module (ARM) of the atrial natriuretic factor receptor guanylate cyclase

Atrial natriuretic factor (ANF) receptor guanylate cyclase (ANF-RGC) is a single chain transmembrane-spanning protein, containing both ANF binding and catalytic activities. ANF binding to the extracellular receptor domain activates the cytosolic catalytic domain, generating the second messenger cyclic GMP. Obligatory in this activation process is an intervening transduction step, which is regulated by the binding of ATP to the cyclase. The partial structural motif of the ATP binding domain of the cyclase has been elucidated and has been termed ATP Regulatory Module (ARM). The crystal structures of the tyrosine kinase domains of the human insulin receptor and haematopoietic cell kinase were used to derive a homology-based model of the ARM domain of ANF-RGC. The model identifies the precise configuration of the ATP-binding pocket in the ARM domain, accurately represents its ATP-dependent features, and shows that the ATP-dependent transduction phenomenon is a two-step mechanism. In the first step, ATP binds to its pocket and changes its configuration; in the second step, via an unknown protein kinase, it phosphorylates the cyclase for its full activation.