Interaction of Human Chloride Intracellular Channel Protein 1 (CLIC1) with Lipid Bilayers: A Fluorescence Study

Abstract

Chloride intracellular channel protein 1 (CLIC1) is very unusual as it adopts a soluble glutathione S-transferase-like canonical fold but can also autoinsert into lipid bilayers to form an ion channel. The conversion between these forms involves a large, but reversible, structural rearrangement of the CLIC1 module. The only identified environmental triggers controlling the metamorphic transition of CLIC1 are pH and oxidation. Until now, there have been no high-resolution structural data available for the CLIC1 integral membrane state, and consequently, a limited understanding of how CLIC1 unfolds and refolds across the bilayer to form a membrane protein with ion channel activity exists. Here we show that fluorescence spectroscopy can be used to establish the interaction and position of CLIC1 in a lipid bilayer. Our method employs a fluorescence energy transfer (FRET) approach between CLIC1 and a dansyl-labeled lipid analogue to probe the CLIC1-lipid interface. Under oxidizing conditions, a strong FRET signal between the single tryptophan residue of CLIC1 (Trp35) and the dansyl-lipid analogue was detected. When considering the proportion of CLIC1 interacting with the lipid bilayer, as estimated by fluorescence quenching experiments, the FRET distance between Trp35 and the dansyl moiety on the membrane surface was determined to be ∼15 Å. This FRET-detected interaction provides direct structural evidence that CLIC1 associates with membranes. The results presented support the current model of an oxidation-driven interaction of CLIC1 with lipid bilayers and also propose a membrane anchoring role for Trp35.

Conformational properties, membrane interaction, and antibacterial activity of the peptaibiotic chalciporin A: Multitechnique spectroscopic and biophysical investigations on the natural compound and labeled analogs

“…The observed substantial enhancement is indicative of an effective membrane binding . This finding is not unexpected considering the overall high hydrophobicity of chalciporin A and the extensively reported ability of an exposed Trp residue to act as a hook for a peptide at an aqueous/membrane interface . The binding curve is comparable to those reported previously for fluorescent analogs of trichogin GA IV (although in membranes of different composition) and is consistent with the similar membrane‐perturbing properties reported above.…”

Inherent flexibility of CLIC6 revealed by crystallographic and solution studies

“…mCLIC6 contains two endogenous tryptophan residues, W390 and W562, which localize to the TRX and α domains, respectively. Similar to CLIC1 32 , 33 , Stern–Volmer plot analysis demonstrate that while exposure of mCLIC6 to increasing concentrations of acrylamide resulted in a progressive quenching of tryptophan fluorescence (K SV = 2.5 ± 0.1 M −1 ), addition of 2 mM H 2 O 2 reduced the acrylamide-induced tryptophan quenching efficiency (K SV = 1.5 ± 0.1 M −1 ), indicating reduced tryptophan accessibility under oxidative conditions. Hence, these observations suggest that mCLIC6 undergoes a conformational rearrangement, triggered by oxidative environment, which possibly leads to exposure of nascent hydrophobic domains.…”

Three Decades of Chloride Intracellular Channel Proteins: From Organelle to Organ Physiology

“…Figure 11.21.2 Sequence and key features in the secondary structure of CLIC1. Key amino acids involved in ion channel properties and membrane anchoring are identified based on structurefunction studies (Averaimo et al, 2013;Gururaja Rao et al, 2017;Hare, Goodchild, Breit, Curmi, & Brown, 2016;Liu et al, 2007;Singh & Ashley, 2006) and are highlighted with red and blue arrows within the transmembrane domain (grey box). The conserved nuclear localization signal (KKYR) is highlighted in the purple text.…”