Bicarbonate and Ca2+ Sensing Modulators Activate Photoreceptor ROS-GC1 Synergistically

Membrane guanylate cyclase (MGC) is a ubiquitous multi-switching cyclic GMP generating signaling machine linked with countless physiological processes. In mammals it is encoded by seven distinct homologous genes. It is a single transmembrane spanning multi-modular protein; composed of integrated blocks and existing in homo-dimeric form. Its core catalytic domain (CCD) module is a common transduction center where all incoming signals are translated into the production of cyclic GMP, a cellular signal second messenger. Crystal structure of the MGC’s CCD does not exist and its precise identity is ill-defined. Here, we define it at a sub-molecular level for the phototransduction-linked MGC, the rod outer segment guanylate cyclase type 1, ROS-GC1. (1) The CCD is a conserved 145-residue structural unit, represented by the segment V820-P964. (2) It exists as a homo-dimer and contains seven conserved catalytic elements (CEs) wedged into seven conserved motifs. (3) It also contains a conserved 21-residue neurocalcin δ-modulated structural domain, V836-L857. (4) Site-directed mutagenesis documents that each of the seven CEs governs the cyclase’s catalytic activity. (5) In contrast to the soluble and the bacterium MGC which use Mn2+-GTP substrate for catalysis, MGC CCD uses the natural Mg2+-GTP substrate. (6) Strikingly, the MGC CCD requires anchoring by the Transmembrane Domain (TMD) to exhibit its major (∼92%) catalytic activity; in isolated form the activity is only marginal. This feature is not linked with any unique sequence of the TMD; there is minimal conservation in TMD. Finally, (7) the seven CEs control each of four phototransduction pathways- -two Ca2+-sensor GCAPs-, one Ca2+-sensor, S100B-, and one bicarbonate-modulated. The findings disclose that the CCD of ROS-GC1 has built-in regulatory elements that control its signal translational activity. Due to conservation of these regulatory elements, it is proposed that these elements also control the physiological activity of other members of MGC family.

Section: Methodsmentioning

confidence: 99%

Membrane Guanylate Cyclase catalytic Subdomain: Structure and Linkage with Calcium Sensors and Bicarbonate

Ravichandran

Duda

Pertzev

et al. 2017

“…It follows that the loss in GCAP1 modulation occurs at the signal transduction level and possibly resides in one or more of the catalytic core residues: D 834 , E 874 , D 878 , R 925 , C 946 , N 953 . In contrast, the mutation does not abolish Ca 2+ -modulation by GCAP2 or by S100B (Duda et al, 1999 , 2016 ), even though the absolute activities are reduced in all conditions. The interaction of this disease-causing mutation with bicarbonate led to some insights into the intramolecular signaling pathways.…”

Section: Introductionmentioning

confidence: 99%

“…The bicarbonate signal transduction of ROS-GC1 occurs independently of [Ca 2+ ] i . Yet, it synergizes with the Ca 2+ -sensors: GCAP1, GCAP2 and S100B to intensify Ca 2+ modulation, particularly for GCAP2 (Duda et al, 2015 , 2016 ). The effect on photoreceptors is to elevate the circulating current, decrease sensitivity to flashes and accelerate flash response recovery.…”

Section: Introductionmentioning

confidence: 99%

“…An F 514 S mutation in ROS-GC1 causes Leber’s congenital amaurosis type 1 blindness in human patients (Perrault et al, 1996 , 1999 ; Rozet et al, 2001 ). There is a 10-fold loss in ROS-GC1 catalytic activity (Duda et al, 1999 ) that is almost totally insensitive to GCAP1 modulation, despite retention of GCAP1 binding to ROS-GC (Duda et al, 2016 ). It follows that the loss in GCAP1 modulation occurs at the signal transduction level and possibly resides in one or more of the catalytic core residues: D 834 , E 874 , D 878 , R 925 , C 946 , N 953 .…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Integrative Signaling Networks of Membrane Guanylate Cyclases: Biochemistry and Physiology

Sharma

Duda

Makino

2016

Self Cite

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.

“… Schematic overview on the modular structure of the rod outer segment guanylyl cyclase 1 (ROS-GC1) dimer. Domain nomenclature is adapted from Duda et al ( 2016 ). LS stands for leader sequence, ExtD, extracellular domain; TmD, transmembrane domain; JmD, juxtamembrane domain; KHD, kinase homology domain; SHD, signaling helix domain; CCD, core catalytic domain and CTE, C -terminal extension.…”

Section: Introductionmentioning

confidence: 99%

Molecular Details of Retinal Guanylyl Cyclase 1/GCAP-2 Interaction

Rehkamp

Tänzler

Iacobucci

et al. 2018

The rod outer segment guanylyl cyclase 1 (ROS-GC1) is an essential component of photo-transduction in the retina. In the light-induced signal cascade, membrane-bound ROS-GC1 restores cGMP levels in the dark in a calcium-dependent manner. With decreasing calcium concentration in the intracellular compartment, ROS-GC1 is activated via the intracellular site by guanylyl cyclase-activating proteins (GCAP-1/-2). Presently, the exact activation mechanism is elusive. To obtain structural insights into the ROS-GC1 regulation by GCAP-2, chemical cross-linking/mass spectrometry studies using GCAP-2 and three ROS-GC1 peptides were performed in the presence and absence of calcium. The majority of cross-links were identified with the C-terminal lobe of GCAP-2 and a peptide comprising parts of ROS-GC1's catalytic domain and C-terminal extension. Consistently with the cross-linking results, surface plasmon resonance and fluorescence measurements confirmed specific binding of this ROS-GC peptide to GCAP-2 with a dissociation constant in the low micromolar range. These results imply that a region of the catalytic domain of ROS-GC1 can participate in the interaction with GCAP-2. Additional binding surfaces upstream of the catalytic domain, in particular the juxtamembrane domain, can currently not be excluded.