Conformational changes during human P2X7 receptor activation examined by structural modelling and cysteine-based cross-linking studies

The P2X7 receptor (P2X7R) is important in mediating a range of physiological functions and pathologies associated with tissue damage and inflammation and represents an attractive therapeutic target. However, in terms of their structure-function relationships, the mammalian P2X7Rs remain poorly characterised compared to some of their other P2XR counterparts. In this study, combining cysteine-based cross-linking and whole-cell patch-clamp recording, we examined six pairs of residues (A44/I331, D48/I331, I58/F311, S60/L320, I75/P177 and K81/V304) located in different parts of the extracellular and transmembrane domains of the human P2X7R. These residues are predicted to undergo substantial movement during the transition of the receptor ion channel from the closed to the open state, predictions which are made based on structural homology models generated from the crystal structures of the zebrafish P2X4R. Our results provide evidence that among the six pairs of cysteine mutants, D48C/I133C and K81C/V304C formed disulphide bonds that impaired the channel gating to support the notion that such conformational changes, particularly those in the outer ends of the transmembrane domains, are critical for human P2X7R activation

Heterologous Expression and Patch-Clamp Recording of P2X Receptors in HEK293 Cells

P2X receptors (P2XRs) are ligand-gated ion channels gated by extracellular adenosine 5′-triphosphate (ATP) and play a critical role in mediating ATP-induced purinergic signaling in physiological and pathological processes. Heterologous expression of P2XR in human embryonic kidney 293 (HEK293) cells and measurement of P2XR-mediated currents using patch-clamp recording technique have been widely used to study the biophysical and pharmacological properties of these receptors. Combination of electrophysiology with site-directed mutagenesis and structural information has shed light on the molecular basis for receptor activation and mechanisms of actions by receptor antagonists and modulators. It is anticipated that such methodologies will continue helping us to provide more mechanistic understanding of P2XRs and to test novel receptor antagonists and allosteric modulators for therapeutical purposes. In this chapter, we describe protocols of transiently or stably expressing the P2XR in HEK293 cells and measuring P2XR-mediated currents by using whole-cell recording

Activation of the P2X7 ion channel by soluble and covalently bound ligands

The homotrimeric P2X7 purinergic receptor has sparked interest because of its capacity to sense adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide (NAD) released from cells and to induce calcium signaling and cell death. Here, we examine the response of arginine mutants of P2X7 to soluble and covalently bound ligands. High concentrations of ecto-ATP gate P2X7 by acting as a soluble ligand and low concentrations of ecto-NAD gate P2X7 following ADP-ribosylation at R125 catalyzed by toxin-related ecto-ADP-ribosyltransferase ART2.2. R125 lies on a prominent cysteine-rich finger at the interface of adjacent receptor subunits, and ADP-ribosylation at this site likely places the common adenine nucleotide moiety into the ligand-binding pocket of P2X7

Neue Missense-Mutation bei sensorischer Tiefton-Schallempfindungsschwerhörigkeit (DFNA 6/14)

Wir stellen die audiometrischen und molekulargenetischen Befunde einer Familie mit DFNA 6/14 vor. Bei der Erkrankung handelt es sich um eine mittelgradige sensorische Tief-Mitteltonschwerhörigkeit, die autosomal dominant vererbt wird. Die erhobenen audiometrischen Befunde stimmen mit den zu DFNA 6/14 bisher publizierten Daten überein. Mit Hilfe der molekulargenetischen Analyse konnte eine neue Missense Mutation des WFS1-Gens aufgedeckt werden. Dieses Gen ist auch als auslösende Ursache des Wolfram-Syndroms Typ 1 (WFS1), welches auch als DIDMOAD-Syndrom (Diabetes mellitus, Diabetes insipidus, Opticusatrophie, Schwerhörigkeit) bezeichnet wird, bekannt (Inoue et al. 1998, ). Auf Grundlage bisher bekannter Daten kann angenommen werden, daß bei WFS1-Patienten (autosomal rezessiver Erbgang) ein Hochton-Empfindungshörverlust auftreten kann . Demgegenüber zeigen autosomal dominant betroffene Patienten einen sensorischen Tief-Mitteltonhörverlust . Die molekulargenetischen und audiometrischen Befunde der hier untersuchten Familie werden dargestellt. Weitere Untersuchungen fokussieren den pathogenetischen Effekt der Mutation resp. des durch die Mutation betroffenen Proteins