Chloride Intracellular Channel Protein 2: Difference between revisions
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<StructureSection load='2r5g' size='450' side='right' scene='Chloride_Intracellular_Channel_Protein_2/Structintro/2' caption='Human CLIC2 (PDB code [[2r5g]])'> | |||
[[Image:Nfig001.jpg|300px|left|thumb| Localization of the different structures of CLIC2]] | |||
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CLIC proteins are a new class of soluble and membrane-bound proteins that have been grouped together on the basis of their sequence similarity. The proteins were named CLIC because the first members of this family to be characterized formed intracellular chloride channels. <ref>PMID:9339381</ref> They display broad tissue and cellular distribution. They have been implicated in kidney function, cell division, and bone resorption. <ref>PMID:18007051</ref> They differ from the other classes of chloride ion channels in primary structure and in the transmembrane regions of the tertiary structure. Since the first member of CLIC, p64 (CLIC5), was discovered in bovine kidney, several members of the CLIC family have been found in other tissues from many species, including NCC27 (CLIC1), CLIC2, CLIC3, mtCLIC (CLIC4), and parchorin (CLIC6). <ref>PMID:19356589</ref> With the exception of p64 and parchorin, these proteins contain a conserved region of approximately 240 residues. <ref>PMID:17945253 </ref> | |||
CLIC proteins can localize to distinct cellular membranes, including the nuclear membrane, lysosomal membranes, mitochondria, Golgi membranes, cell–cell junctions, and the plasma membrane. <ref>PMID:18007051</ref> | |||
CLIC proteins are a new class of soluble and membrane-bound proteins that have been grouped together on the basis of their sequence similarity. The proteins were named CLIC because the first members of this family to be characterized formed intracellular chloride channels. <ref>PMID:9339381</ref> They display broad tissue and cellular distribution. They have been implicated in kidney function, cell division, and bone resorption. <ref>PMID:18007051</ref> They differ from the other classes of chloride ion channels in primary structure and in the transmembrane regions of the tertiary structure. Since the first member of CLIC, p64 (CLIC5), was discovered in bovine kidney, several members of the CLIC family have been found in other tissues from many species, including NCC27 (CLIC1), CLIC2, CLIC3, mtCLIC (CLIC4), and parchorin (CLIC6). | |||
CLIC proteins can localize to distinct cellular membranes, including the nuclear membrane, lysosomal membranes, mitochondria, Golgi membranes, cell–cell junctions, and the plasma membrane. | |||
The CLIC proteins show sequence homology with members of the glutathione-S-transferase (GST) superfamily. | The CLIC proteins show sequence homology with members of the glutathione-S-transferase (GST) superfamily. | ||
Another feature of CLIC proteins distinguishable from other ion channels is that they exist in two different forms: either as soluble globular proteins, or as an integral membrane protein that is incorporated into lipid bilayers and forms ion channels. | Another feature of CLIC proteins distinguishable from other ion channels is that they exist in two different forms: either as soluble globular proteins, or as an integral membrane protein that is incorporated into lipid bilayers and forms ion channels. <ref>PMID:19356589</ref> These features that are reminiscent of many bacterial pore-forming toxins. <ref>PMID:17945253 </ref> | ||
CLIC2 is one of the least characterized CLIC family members. At least two isoforms are known to exist, with the difference being an 18-residue insert occurring immediately after the first β-strand. | CLIC2 is one of the least characterized CLIC family members. At least two isoforms are known to exist, with the difference being an 18-residue insert occurring immediately after the first β-strand. <ref>PMID:18007051</ref> It has a molecular weight of 28.4 kDa and a calculated isoelectric point of 5.44. <ref>PMID:18280248 </ref> Human CLIC2 protein is composed of 247 amino acid residues and is found in many organs, including the spleen, lung, liver, and in both skeletal and cardiac muscles. <ref>PMID:19356589</ref> The CLIC2 gene locates in the telomeric region of Xq28 and is composed of six coding exons and five introns. Since this region of the X chromosome is closely associated with many hereditary diseases, CLIC2 has thus been proposed as a candidate gene for some genetic disorders linked to Xq28.9. <ref>PMID:18186468</ref> Consistent with their high degree of primary structure homology, CLIC2 is similar to CLIC1 and CLIC4 in terms of tertiary structure. Like other members of the CLIC family, CLIC2 can exist as a soluble globular protein, or incorporated into a lipid bilayer to form a Cl– channel. <ref>PMID:19356589</ref> | ||
CLIC2 inhibits cardiac ryanodine receptor (RyR) calciumrelease channels, suggesting that CLIC2 may function to regulate calcium release from intracellular stores in the heart and skeletal muscles. | CLIC2 inhibits cardiac ryanodine receptor (RyR) calciumrelease channels, suggesting that CLIC2 may function to regulate calcium release from intracellular stores in the heart and skeletal muscles. <ref>PMID:18007051</ref> The N-terminal domain of CLIC2 lacks the cysteine equivalent to Cys59 of CLIC1, but contains another cysteine Cys33 that together with the conserved Cys30 (equivalent to Cys24 in CLIC1) forms a CxxC motif similar to glutaredoxin.<ref>PMID:17945253 </ref> | ||
== Structure == | == Structure == | ||
[[Image:0.jpg | [[Image:0.jpg|left|300px|thumb''Two different forms of CLIC2 which differ by 18 residues: form A (blue) and form B (grey).'']] | ||
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''Two different forms of | |||
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Contrary to each members of the CLICs family, CLIC 2 is a monomer, no matter if it is oxydated or reduiced. It is composed of 247 amino acids, has a weight of 28.4kDa and an isoelectric point at 5.44(crystal structure). The CLIC2 molecule is box shaped (60×60×35 Å) and consists of a four strand core and two helices on one side. Comparing sequence similarities, the core is supposed to adopt the canonical fold of the glutathione S-transferase (GST) superfamily. This has been confirmed by the crystal structure determination of human CLIC1 at 1.4 Å resolution. Then, by analyzing CLIC genes sequences, this protein appears to have two potential transmembrane domains that would correspond to helices α1 and α6 in the GST-like structure of the soluble form. Thanks to immunological, electrophysical and proteolysis studies, we can say that membrane form of CLIC proteins cross the lipid bilayer an odd number of times. | Contrary to each members of the CLICs family, CLIC 2 is a monomer, no matter if it is oxydated or reduiced. It is composed of 247 amino acids, has a weight of 28.4kDa and an isoelectric point at 5.44(crystal structure). The CLIC2 molecule is box shaped (60×60×35 Å) and consists of a four strand core and two helices on one side. Comparing sequence similarities, the core is supposed to adopt the canonical fold of the glutathione S-transferase (GST) superfamily. This has been confirmed by the crystal structure determination of human CLIC1 at 1.4 Å resolution. Then, by analyzing CLIC genes sequences, this protein appears to have two potential transmembrane domains that would correspond to helices α1 and α6 in the GST-like structure of the soluble form. Thanks to immunological, electrophysical and proteolysis studies, we can say that membrane form of CLIC proteins cross the lipid bilayer an odd number of times. | ||
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===Similarity to other CLIC structures=== | ===Similarity to other CLIC structures=== | ||
CLIC4 ([ | CLIC4 ([[2ahe]]) resolution 1.80Å (residues 58-75)' /> | ||
An interesting thing to do is to compare CLIC2 to other CLIC proteins to understand why they are distinguished. | An interesting thing to do is to compare CLIC2 to other CLIC proteins to understand why they are distinguished. | ||
Conserved regions in the glutathione S-transferase (GST) superfamily members appear to have a functional role since CLIC1 can interact with GST thanks to these regions. However, CLIC2 lost most of residues of CLIC1 that interact with GST except Lys 19 (<scene name='Sandbox123/Lys13/1'>Lys 13</scene> in CLIC1) and Cys 30 ( <scene name='Sandbox123/Cys_24/2'>Cys 24</scene> in CLIC1). In CLIC1, Lys 13 interacts with a glycyl carboxylate on GSH and Cys 24 forms a mixed disulfide bridge with GSH. The intramolecular disulfide bridge between Cys 30 and Cys 33 in CLIC2 prevents form binding between CLIC2 and GST. As a conclusion, between CLIC1 and CLIC2, the first difference is the loss of the GST binding site in CLIC2. | Conserved regions in the glutathione S-transferase (GST) superfamily members appear to have a functional role since CLIC1 can interact with GST thanks to these regions. However, CLIC2 lost most of residues of CLIC1 that interact with GST except Lys 19 (<scene name='Sandbox123/Lys13/1'>Lys 13</scene> in CLIC1) and Cys 30 ( <scene name='Sandbox123/Cys_24/2'>Cys 24</scene> in CLIC1). In CLIC1, Lys 13 interacts with a glycyl carboxylate on GSH and Cys 24 forms a mixed disulfide bridge with GSH. The intramolecular disulfide bridge between Cys 30 and Cys 33 in CLIC2 prevents form binding between CLIC2 and GST. As a conclusion, between CLIC1 and CLIC2, the first difference is the loss of the GST binding site in CLIC2. | ||
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What’s more, CLIC-2 has also a light catalytic activity glutathione transferase. | What’s more, CLIC-2 has also a light catalytic activity glutathione transferase. | ||
CLIC2 interacts with the RyR protein (those channels are called Ryanodine receptor RyR). and has by this interaction a huge role in calcium concentration regulation. Actually, CLIC2 is involved in maintaining calcium homeostasy by limiting calcium releases for cellular stock. | CLIC2 interacts with the RyR protein (those channels are called Ryanodine receptor RyR). and has by this interaction a huge role in calcium concentration regulation. Actually, CLIC2 is involved in maintaining calcium homeostasy by limiting calcium releases for cellular stock. | ||
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Ryanodine is an alkaloid extracted from plants which modify the activity of intracellular chloride channels like those present on sarcoplasmic reticulum. At low concentrations (<10µM), ryanodine opens RyR leading to calcium release in the cytoplasm from the sarcoplasmic reticulum. Whereas at high concentrations (>100µM), ryanodine inhibits RyR.. | Ryanodine is an alkaloid extracted from plants which modify the activity of intracellular chloride channels like those present on sarcoplasmic reticulum. At low concentrations (<10µM), ryanodine opens RyR leading to calcium release in the cytoplasm from the sarcoplasmic reticulum. Whereas at high concentrations (>100µM), ryanodine inhibits RyR.. | ||
Furthermore, the binding of CLIC2 to domains 5 and 6 of RyR increases the interaction between these two domains and so stabilizes the closed state of the RyR channel. This aspect explain how CLIC2 can prevent from Ca2+ efflux from skeletal heavy sarcoplasmic reticulum. | Furthermore, the binding of CLIC2 to domains 5 and 6 of RyR increases the interaction between these two domains and so stabilizes the closed state of the RyR channel. This aspect explain how CLIC2 can prevent from Ca2+ efflux from skeletal heavy sarcoplasmic reticulum. | ||
A detail that worth being noticed, it is the fact that a small fraction of cardiac RyR or not totally inhibited by CLIC2. This can be explained by supposing that there exist many isoforms of RyR or simply because we still do not really know if CLIC2 interacts directly with RyR or with other component of the RyR complex. | A detail that worth being noticed, it is the fact that a small fraction of cardiac RyR or not totally inhibited by CLIC2. This can be explained by supposing that there exist many isoforms of RyR or simply because we still do not really know if CLIC2 interacts directly with RyR or with other component of the RyR complex. | ||
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In addition with CLIC2, ryanodine and GST, RyR has many regulators including Ca2+ and Mg2+, ATP and calmodulin. All these regulators allow RyR channels to respond in synchrony with other cell processes even if CLIC2 remains one of the only a few cytosolic inhibitors of cardiac RyR2 channels, and may suppress their activity during diastole and during stress. The action of CLIC-2 in depressing RyR channel activity and regulating cytoplasmic Ca2+ stores suggests indirectly that it could be effective in preventing or reducing Ca2+ overload in conditions such as ischaemia, and in slowing apoptotic processes. | In addition with CLIC2, ryanodine and GST, RyR has many regulators including Ca2+ and Mg2+, ATP and calmodulin. All these regulators allow RyR channels to respond in synchrony with other cell processes even if CLIC2 remains one of the only a few cytosolic inhibitors of cardiac RyR2 channels, and may suppress their activity during diastole and during stress. The action of CLIC-2 in depressing RyR channel activity and regulating cytoplasmic Ca2+ stores suggests indirectly that it could be effective in preventing or reducing Ca2+ overload in conditions such as ischaemia, and in slowing apoptotic processes. | ||
Those receptors are also involved in the physical bound to the sarcoplasmic reticulum and transversal tubules in squeletal muscle cells | |||
</StructureSection> | |||
__NOTOC__ | |||
==3D structures of Chloride intracellular channel proteins== | |||
[[Ion channels]] | |||
==Additional Resources== | ==Additional Resources== | ||
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== References == | == References == | ||
<references/> | <references/> | ||
'''5,5'-Dithio-bis(2-nitrobenzoic acid) modification of cysteine improves the crystal quality of human chloride intracellular channel protein 2.''' | '''5,5'-Dithio-bis(2-nitrobenzoic acid) modification of cysteine improves the crystal quality of human chloride intracellular channel protein 2.''' | ||
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Proteins. 2008 Apr. PMID: 18186468 | Proteins. 2008 Apr. PMID: 18186468 | ||
'''Blood leukocyte microarrays to diagnose systemic onset juvenile idiopathic arthritis and follow the response to IL-1 blockade''' | '''Blood leukocyte microarrays to diagnose systemic onset juvenile idiopathic arthritis and follow the response to IL-1 blockade''' | ||