Biochemistry - Metamorphic proteins

MRC Centre for Protein Engineering, Hills Road, Cambridge CB2 0QH, UK.
Science (Impact Factor: 33.61). 07/2008; 320(5884):1725-6. DOI: 10.1126/science.1158868
Source: PubMed


Proteins that can adopt more than one native folded conformation may be more common than previously thought.

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    • "CLIC1 is a metamorphic protein that can shift between two or more different stable conformations [8,9,10]. It exists largely as a soluble intracellular protein but under appropriate conditions can insert into lipid membranes [4,11,12,13]. "
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    ABSTRACT: Chloride intracellular Channel 1 (CLIC1) is a metamorphic protein that changes from a soluble cytoplasmic protein into a transmembrane protein. Once inserted into membranes, CLIC1 multimerises and is able to form chloride selective ion channels. Whilst CLIC1 behaves as an ion channel both in cells and in artificial lipid bilayers, its structure in the soluble form has led to some uncertainty as to whether it really is an ion channel protein. CLIC1 has a single putative transmembrane region that contains only two charged residues: arginine 29 (Arg29) and lysine 37 (Lys37). As charged residues are likely to have a key role in ion channel function, we hypothesized that mutating them to neutral alanine to generate K37A and R29A CLIC1 would alter the electrophysiological characteristics of CLIC1. By using three different electrophysiological approaches: i) single channel Tip-Dip in artificial bilayers using soluble recombinant CLIC1, ii) cell-attached and iii) whole-cell patch clamp recordings in transiently transfected HEK cells, we determined that the K37A mutation altered the single-channel conductance while the R29A mutation affected the single-channel open probability in response to variation in membrane potential. Our results show that mutation of the two charged amino acids (K37 and R29) in the putative transmembrane region of CLIC1 alters the biophysical properties of the ion channel in both artificial bilayers and cells. Hence these charged residues are directly involved in regulating its ion channel activity. This strongly suggests that, despite its unusual structure, CLIC1 itself is able to form a chloride ion channel.
    PLoS ONE 09/2013; 8(9):e74523. DOI:10.1371/journal.pone.0074523 · 3.23 Impact Factor
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    • "The transition between the two soluble states arises via a large rearrangement of the CLIC1 N-terminal domain under the influence of oxidation[7]. Because of this, it has been included into the recently classed family of “metamorphic” proteins[14]. It is postulated that rearrangement of the highly ‘plastic’ N-terminal domain is necessary for the protein's ability to auto-insert into a membrane environment [7], [15], [16], [17], [18]. "
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    ABSTRACT: The Chloride Intracellular ion channel protein CLIC1 has the ability to spontaneously insert into lipid membranes from a soluble, globular state. The precise mechanism of how this occurs and what regulates this insertion is still largely unknown, although factors such as pH and redox environment are known contributors. In the current study, we demonstrate that the presence and concentration of cholesterol in the membrane regulates the spontaneous insertion of CLIC1 into the membrane as well as its ion channel activity. The study employed pressure versus area change measurements of Langmuir lipid monolayer films; and impedance spectroscopy measurements using tethered bilayer membranes to monitor membrane conductance during and following the addition of CLIC1 protein. The observed cholesterol dependent behaviour of CLIC1 is highly reminiscent of the cholesterol-dependent-cytolysin family of bacterial pore-forming proteins, suggesting common regulatory mechanisms for spontaneous protein insertion into the membrane bilayer.
    PLoS ONE 02/2013; 8(2):e56948. DOI:10.1371/journal.pone.0056948 · 3.23 Impact Factor
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    • "Our recent studies have revealed that the D-state consists of dynamically disordered and ordered domains, with the ordered domain stabilizing two high-energy cis peptidyl–prolyl bonds, which are trans in the Sstate [16]. Thus, IscU can be classified as a metamorphic protein [17], a protein that can adopt two different folds. This raises the questions: why has IscU evolved to be metamorphic, and do the two different conformations play physiologically important roles? "
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    ABSTRACT: IscU from Escherichia coli, the scaffold protein for iron-sulfur cluster biosynthesis and delivery, populates a complex energy landscape. IscU exists as two slowly interconverting species: one (S) is largely structured with all four peptidyl-prolyl bonds trans; the other (D) is partly disordered but contains an ordered domain that stabilizes two cis peptidyl-prolyl peptide bonds. At pH 8.0, the S-state is maximally populated at 25 °C, but its population decreases at higher or lower temperatures or at lower pH. The D-state binds preferentially to the cysteine desulfurase (IscS), which generates and transfers sulfur to IscU cysteine residues to form persulfides. The S-state is stabilized by Fe-S cluster binding and interacts preferentially with the DnaJ-type co-chaperone (HscB), which targets the holo-IscU:HscB complex to the DnaK-type chaperone (HscA) in its ATP-bound from. HscA is involved in delivery of Fe-S clusters to acceptor proteins by a mechanism dependent on ATP hydrolysis. Upon conversion of ATP to ADP, HscA binds the D-state of IscU ensuring release of the cluster and HscB. These findings have led to a more complete model for cluster biosynthesis and delivery.
    FEBS letters 01/2013; 587(8). DOI:10.1016/j.febslet.2013.01.003 · 3.17 Impact Factor
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