Molecular transduction in receptor-ligand systems by planar electromagnetic fields

The coupling of a ligand with a molecular receptor induces a signal that travels through the receptor, reaching the internal domain and triggering a response cascade. In previous work on T-cell receptors and their coupling with foreign antigens, we observed the presence of planar molecular patterns able to generate electromagnetic fields within the proteins. These planes showed a coherent (synchronized) behavior, replicating immediately in the intracellular domain that which occurred in the extracellular domain as the ligand was coupled. In the present study, we examined this molecular transduction - the capacity of the coupling signal to penetrate deep inside the receptor molecule and induce a response. We verified the presence of synchronized behavior in diverse receptor-ligand systems. To appreciate this diversity, we present four biochemically different systems - TCR-peptide, calcium pump-ADP, haemoglobin-oxygen, and gp120-CD4 viral coupling. The confirmation of synchronized molecular transduction in each of these systems suggests that the proposed mechanism would occur in all biochemical receptor-ligand systems.

Non-glycosylated Seipin to Cause a Motor Neuron Disease Induces ER stress and Apoptosis by Inactivating the ER Calcium Pump SERCA2b

ABSTRACTA causal relationship between endoplasmic reticulum (ER) stress and the development of neurodegenerative diseases remains controversial. Here, we focused on Seipinopathy, a dominant motor neuron disease, based on the finding that its causal gene product, Seipin, is a hairpin-like transmembrane protein in the ER. Gain-of-function mutations of Seipin produce non-glycosylated Seipin (ngSeipin), which was previously shown to induce ER stress and apoptosis at both cell and mouse levels albeit with no clarified mechanism. We found that aggregation-prone ngSeipin dominantly inactivated SERCA2b, the major calcium pump in the ER, and decreased the calcium concentration in the ER, leading to ER stress and apoptosis. This inactivation required oligomerization of ngSeipin and direct interaction of the ngSeipin C-terminus with SERCA2b, and was observed in Seipin-deficient human colorectal carcinoma-derived cells (HCT116) expressing ngSeipin at a level comparable with that in neuroblastoma cells (SH-SY5T). Our results thus provide a new direction to controversy noted above.

Effect of Angiotensin 1-7 on Myocardial Calcium Pump in Salt-Sensitive Hypertensive Rats

Objective — To investigate the effects of angiotensin 1-7 (Ang1-7) on plasma membrane ATPase isoform 1 (PMCA1) in salt-sensitive hypertensive rats. Methods — Thirty newborn male Wistar rats were selected to establish the salt-sensitive hypertensive rat model with sensory nerve injury, which were then randomly divided into 5 groups (n=5), including model group, Telmisartan group, Ramipril group, Ang1-7 group, and A-779 group. Another normal control group was established (n=5). After 4 weeks of intervention, the tail blood pressure of rats in each group was measured, and then the apical tissue of left ventricle was cut. The contents of AngⅡ and Ang1-7 in cardiomyocytes were detected by enzyme-linked immunosorbent assay. The expression of PMCA1 mRNA and protein in heart of salt-sensitive hypertensive rats were detected by RT-PCR and immunohistochemistry. Results — (1) Compared with the normal control group, the concentration of AngⅡ in the myocardium of salt-sensitive hypertensive rats increased (P < 0.05), which decreased after the intervention of Telmisartan and Ramipril (P < 0.05), and no change occurred after the intervention of Ang1-7 in concentration (P＞0.05). (2) Compared with the normal control group, the concentration of myocardial Ang1-7 in salt-sensitive hypertensive rats decreased (P < 0.05), and increased after the intervention of telmisartan and ramipril (P < 0.05), and increased after the intervention of A-779 (P < 0.05). (3) The expression of PMCA1 mRNA and protein in salt-sensitive hypertensive rats was increased compared with the normal control group (P < 0.05), and the expression of Ang-(1-7), telmisartan and ramipril was decreased compared with the model group (P < 0.05). The expression of p38MAPK mRNA and p-p38MAPK protein in the myocardium of salt-sensitive hypertensive rats was increased compared with that in the normal control group (P < 0.05), and the expression of Ang-(1-7), Telmisartan and Ramipril was decreased compared with that in the model group (P < 0.05). Conclusion — Ang-(1-7) may be involved in the regulation of cardiac calcium pump, inhibiting its overcompensation and delaying the occurrence of calcium pump inhibition in the early stage of salt-sensitive hypertension. Ang-(1-7) can inhibit the activity of p38MAPK and protect the heart, and its regulation on PMCA1 may be mediated by the expression of p38MAPK pathway.

Modulation of the Human Erythroid Plasma Membrane Calcium Pump (PMCA4b) Expression by Polymorphic Genetic Variants

In the human ATP2B4 gene, coding for the plasma membrane calcium pump PMCA4b, a minor haplotype results in the decreased expression of this membrane protein in erythroid cells. The presence of this haplotype and the consequently reduced PMCA4b expression have been suggested to affect red blood cell hydration and malaria susceptibility. By using dual-luciferase reporter assays, we have localized the erythroid-specific regulatory region within the haplotype of the ATP2B4 gene, containing predicted GATA1 binding sites that are affected by SNPs in the minor haplotype. Our results show that, in human erythroid cells, the regulation of ATP2B4 gene expression is significantly affected by GATA1 expression, and we document the role of specific SNPs involved in predicted GATA1 binding. Our findings provide a mechanistic explanation at the molecular level for the reduced erythroid-specific PMCA4b expression in carriers of ATP2B4 gene polymorphic variants.

Dwarf open reading frame (DWORF) is a direct activator of the sarcoplasmic reticulum calcium pump SERCA

The sarcoplasmic reticulum calcium pump SERCA plays a critical role in the contraction-relaxation cycle of muscle. In cardiac muscle, SERCA is regulated by the inhibitor phospholamban. A new regulator, dwarf open reading frame (DWORF), has been reported to displace phospholamban from SERCA. Here, we show that DWORF is a direct activator of SERCA, increasing its turnover rate in the absence of phospholamban. Measurement of in-cell calcium dynamics supports this observation and demonstrates that DWORF increases SERCA-dependent calcium reuptake. These functional observations reveal opposing effects of DWORF activation and phospholamban inhibition of SERCA. To gain mechanistic insight into SERCA activation, fluorescence resonance energy transfer experiments revealed that DWORF has a higher affinity for SERCA in the presence of calcium. Molecular modeling and molecular dynamics simulations provide a model for DWORF activation of SERCA, where DWORF modulates the membrane bilayer and stabilizes the conformations of SERCA that predominate during elevated cytosolic calcium.

Structural Basis for the Function of the C-Terminal Proton Re-Lease Pathway in the Calcium Pump

The calcium pump (sarco/endoplasmic reticulum Ca2+-ATPase, SERCA) plays a major role in calcium homeostasis in muscle cells by clearing cytosolic Ca2+ during muscle relaxation. Active Ca2+ transport by SERCA involves the structural transition from a low-Ca2+ affinity E2 state toward a high-Ca2+ affinity E1 state of the pump. This structural transition is accompanied by the countertransport of protons to stabilize the negative charge and maintain the structural integrity of the transport sites and partially compensate for the positive charges of the two Ca2+ ions passing through the membrane. X-ray crystallography studies have suggested that a hydrated pore located at the C-terminal domain of SERCA serves as a conduit for proton countertransport, but the existence and function of this pathway have not yet been fully characterized. We used atomistic simulations to demonstrate that in the protonated E2 state and the absence of initially bound water molecules, the C-terminal pore becomes hydrated in the nanosecond timescale. Hydration of the C-terminal pore is accompanied by the formation of water wires that connect the transport sites with the cytosol. Water wires are known as ubiquitous proton-transport devices in biological systems, thus supporting the notion that the C-terminal domain serves as a conduit for proton release. Additional simulations showed that the release of a single proton from the transport sites induces bending of transmembrane helix M5 and the interaction between residues Arg762 and Ser915. These structural changes create a physical barrier against full hydration of the pore and prevent the formation of hydrogen-bonded water wires once proton transport has occurred through this pore. Together, these findings support the notion that the C-terminal proton release pathway is a functional element of SERCA and also provide a mechanistic model for its operation in the catalytic cycle of the pump.