Group:MUZIC:CapZ: Difference between revisions
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CapZ is expressed in all eukaryotic cells. It binds to the fast growing barbed ends of [[actin]] filaments and blocks G-actin association and disassociation, thus regulating actin filament dynamics. In skeletal muscle it localizes at the Z-disk. | CapZ is expressed in all eukaryotic cells. It binds to the fast growing barbed ends of [[actin]] filaments and blocks G-actin association and disassociation, thus regulating actin filament dynamics. In skeletal muscle it localizes at the Z-disk. | ||
CapZ is a heterodimer composed of two subunits <scene name='User:Mara_Camelia_Rusu/Workbench/CapZ/Alpha_subunit/1'>α</scene> and <scene name='User:Mara_Camelia_Rusu/Workbench/CapZ/Beta_subunit/1'>β</scene> and there are at least two isoforms of each of the subunits. In cardiomyocites the β1 containing isoform localizes to the Z-disk and β2 containing isoform localizes to the cell periphery and intercalated disc. | |||
The crystal structure of the sarcomeric form has been resolved to a resolution of 2.1 Å by X-ray crystallography (1IZN). <ref>PMID:12660160</ref> | The crystal structure of the sarcomeric form has been resolved to a resolution of 2.1 Å by X-ray crystallography (1IZN). <ref>PMID:12660160</ref> | ||
<Structure load='1IZN' size='500' frame='true' align='right' caption='Crystal structure of chicken CapZ expressed in E.coli' scene='Insert optional scene name here' /> | <Structure load='1IZN' size='500' frame='true' align='right' caption='Crystal structure of chicken CapZ expressed in E.coli' scene='Insert optional scene name here' /> | ||
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== Structure == | == Structure == | ||
CapZ was shown to be a heterodimer with α and β subunits of 286 and 277 residues, respectively. It is a mixed α-helix and β-sheet protein. CapZ has an elongated structure, with overall dimensions of~90 x 50 x55 Å. The CapZ dimer has a pseudo two-fold symmetry, with the monomers joining together to form a central 10-stranded antiparallel <scene name='User:Mara_Camelia_Rusu/Workbench/CapZ/Central_b_sheet/1'>a central 10-stranded β-sheet</scene>. This creates an elongated molecule with the N- and C-terminus of each monomer on opposite faces of the central β -sheet. The C-termini of the subdomains are at opposite ends of the elongated molecule. | |||
One | One CapZ heterodimer appears to be able to bind two actin molecules; this may explain why it is selective for the F-actin barbed end as opposed to monomeric G-actin. CapZ is thought to bind between actin subdomains 1 and 3 (the barbed-end). CapZ also binds a spectrin domain of α-actinin and the C-terminus of nebulin <ref>PMID:15583864</ref>. | ||
== Function and Interactions== | == Function and Interactions== | ||
Capping protein binds to the barbed end with high affinity (Kd > 1 nM) and the stoichiometry is 1:1 and it prevents the loss and addition of actin monomers. | Capping protein binds to the barbed end with high affinity (Kd > 1 nM) and the stoichiometry is 1:1 and it prevents the loss and addition of actin monomers. CapZ is important in the dynamics of actin filaments as it is crucial for rapid filament elongation as a response to signaling. It does so by blocking the barbed ends, thus ensuring a high steady state concentration of G-actin in the cytoplasm <ref>PMID:12660160</ref>. The absence of capping protein prevented the reconstruction of motility in ''Shigella'' and ''Listeria'', ''in vitro''. | ||
CapZ plays a role in targeting the actin filaments to other structural components. The sarcomeric isoform interacts with α-actinin and anchors the thin filament system to the Z-disk <ref>PMID:16416311</ref> | CapZ plays a role in targeting the actin filaments to other structural components. The sarcomeric isoform interacts with α-actinin and anchors the thin filament system to the Z-disk <ref>PMID:16416311</ref> | ||
Small interference RNA (siRNA) studies showed that knockdown of nebulin in chick skeletal myotubes leads to a reduction of assembled CapZ and a loss of the characteristic uniform alignment of the barbed ends of F-actin and this suggests that the interaction of | Small interference RNA (siRNA) studies showed that knockdown of nebulin in chick skeletal myotubes leads to a reduction of assembled CapZ and a loss of the characteristic uniform alignment of the barbed ends of F-actin and this suggests that the interaction of CapZ and nebulin plays a very important role in Z-disk architecture <ref>PMID:18272787</ref>. | ||
CapZ regulates the activity of cardiac protein kinase C (PKC): down regulation of CapZ leads to a decrease and alteration of the PKC signaling pathways. Cardiac CapZ regulates binding of PKC II to the myofilaments with effects on cardiac contractility <ref>PMID:21257757</ref>. | |||
Other binding partners of | Other binding partners of CapZ include the CARMIL protein which further interacts with Arp complex2/3 and myosin I, both of which are key players in actin based cell motility <ref>PMID:12660160</ref>. | ||
In vivo the capping of actin filaments is regulated by second messengers PIP and PIP 2 (Phosphatidylinositol 4,5-bisphosphate), upon signal transduction these molecules promote removal of | In vivo the capping of actin filaments is regulated by second messengers PIP and PIP 2 (Phosphatidylinositol 4,5-bisphosphate), upon signal transduction these molecules promote removal of CapZ from actin filaments <ref>PMID:12663865</ref>. | ||
== Actin binding model == | == Actin binding model == | ||
Proposed by Narita ''et al'' <ref>PMID:17110933</ref> | Proposed by Narita ''et al'' <ref>PMID:17110933</ref> | ||
First, | First, CapZ is attracted to the barbed-end of the actin filament through the electrostatic interactions between the basic residues, which are mainly but not exclusively on/around the α-tentacle and the acidic residues on the extreme surface at the barbed-end of the actin filament. The electrostatic interactions through the α-tentacle may be the major determining factors of the on-rate of the binding. This is because the deletion of the β-tentacle altered only the off-rate of the binding, without changing the on-rate. In contrast, the deletion of the a-tentacle reduced both the on- and off rates. | ||
Second, the β-tentacle finds the hydrophobic binding site on the front surface of actin. The binding of the b-tentacle acts as a lock, and thus reduces the off-rate as suggested previously. | Second, the β-tentacle finds the hydrophobic binding site on the front surface of actin. The binding of the b-tentacle acts as a lock, and thus reduces the off-rate as suggested previously. | ||
This two-step binding mechanism implies that the binding is possible even without the β-tentacle. This is because the first step alone fulfills two requirements for the barbed-end capping: the recognition of the barbed-end and the inhibition of polymerization and depolymerization. | This two-step binding mechanism implies that the binding is possible even without the β-tentacle. This is because the first step alone fulfills two requirements for the barbed-end capping: the recognition of the barbed-end and the inhibition of polymerization and depolymerization. | ||
Revision as of 11:29, 4 October 2012
IntroductionIntroduction
CapZ is expressed in all eukaryotic cells. It binds to the fast growing barbed ends of actin filaments and blocks G-actin association and disassociation, thus regulating actin filament dynamics. In skeletal muscle it localizes at the Z-disk. CapZ is a heterodimer composed of two subunits and and there are at least two isoforms of each of the subunits. In cardiomyocites the β1 containing isoform localizes to the Z-disk and β2 containing isoform localizes to the cell periphery and intercalated disc. The crystal structure of the sarcomeric form has been resolved to a resolution of 2.1 Å by X-ray crystallography (1IZN). [1]
|
StructureStructure
CapZ was shown to be a heterodimer with α and β subunits of 286 and 277 residues, respectively. It is a mixed α-helix and β-sheet protein. CapZ has an elongated structure, with overall dimensions of~90 x 50 x55 Å. The CapZ dimer has a pseudo two-fold symmetry, with the monomers joining together to form a central 10-stranded antiparallel . This creates an elongated molecule with the N- and C-terminus of each monomer on opposite faces of the central β -sheet. The C-termini of the subdomains are at opposite ends of the elongated molecule. One CapZ heterodimer appears to be able to bind two actin molecules; this may explain why it is selective for the F-actin barbed end as opposed to monomeric G-actin. CapZ is thought to bind between actin subdomains 1 and 3 (the barbed-end). CapZ also binds a spectrin domain of α-actinin and the C-terminus of nebulin [2].
Function and InteractionsFunction and Interactions
Capping protein binds to the barbed end with high affinity (Kd > 1 nM) and the stoichiometry is 1:1 and it prevents the loss and addition of actin monomers. CapZ is important in the dynamics of actin filaments as it is crucial for rapid filament elongation as a response to signaling. It does so by blocking the barbed ends, thus ensuring a high steady state concentration of G-actin in the cytoplasm [3]. The absence of capping protein prevented the reconstruction of motility in Shigella and Listeria, in vitro. CapZ plays a role in targeting the actin filaments to other structural components. The sarcomeric isoform interacts with α-actinin and anchors the thin filament system to the Z-disk [4] Small interference RNA (siRNA) studies showed that knockdown of nebulin in chick skeletal myotubes leads to a reduction of assembled CapZ and a loss of the characteristic uniform alignment of the barbed ends of F-actin and this suggests that the interaction of CapZ and nebulin plays a very important role in Z-disk architecture [5]. CapZ regulates the activity of cardiac protein kinase C (PKC): down regulation of CapZ leads to a decrease and alteration of the PKC signaling pathways. Cardiac CapZ regulates binding of PKC II to the myofilaments with effects on cardiac contractility [6]. Other binding partners of CapZ include the CARMIL protein which further interacts with Arp complex2/3 and myosin I, both of which are key players in actin based cell motility [7]. In vivo the capping of actin filaments is regulated by second messengers PIP and PIP 2 (Phosphatidylinositol 4,5-bisphosphate), upon signal transduction these molecules promote removal of CapZ from actin filaments [8].
Actin binding modelActin binding model
Proposed by Narita et al [9]
First, CapZ is attracted to the barbed-end of the actin filament through the electrostatic interactions between the basic residues, which are mainly but not exclusively on/around the α-tentacle and the acidic residues on the extreme surface at the barbed-end of the actin filament. The electrostatic interactions through the α-tentacle may be the major determining factors of the on-rate of the binding. This is because the deletion of the β-tentacle altered only the off-rate of the binding, without changing the on-rate. In contrast, the deletion of the a-tentacle reduced both the on- and off rates. Second, the β-tentacle finds the hydrophobic binding site on the front surface of actin. The binding of the b-tentacle acts as a lock, and thus reduces the off-rate as suggested previously. This two-step binding mechanism implies that the binding is possible even without the β-tentacle. This is because the first step alone fulfills two requirements for the barbed-end capping: the recognition of the barbed-end and the inhibition of polymerization and depolymerization.
ReferencesReferences
- ↑ Yamashita A, Maeda K, Maeda Y. Crystal structure of CapZ: structural basis for actin filament barbed end capping. EMBO J. 2003 Apr 1;22(7):1529-38. PMID:12660160 doi:10.1093/emboj/cdg167
- ↑ Au Y. The muscle ultrastructure: a structural perspective of the sarcomere. Cell Mol Life Sci. 2004 Dec;61(24):3016-33. PMID:15583864 doi:10.1007/s00018-004-4282-x
- ↑ Yamashita A, Maeda K, Maeda Y. Crystal structure of CapZ: structural basis for actin filament barbed end capping. EMBO J. 2003 Apr 1;22(7):1529-38. PMID:12660160 doi:10.1093/emboj/cdg167
- ↑ Frank D, Kuhn C, Katus HA, Frey N. The sarcomeric Z-disc: a nodal point in signalling and disease. J Mol Med. 2006 Jun;84(6):446-68. Epub 2006 Jan 17. PMID:16416311 doi:10.1007/s00109-005-0033-1
- ↑ Pappas CT, Bhattacharya N, Cooper JA, Gregorio CC. Nebulin interacts with CapZ and regulates thin filament architecture within the Z-disc. Mol Biol Cell. 2008 May;19(5):1837-47. Epub 2008 Feb 13. PMID:18272787 doi:10.1091/mbc.E07-07-0690
- ↑ Frank D, Frey N. Cardiac Z-disc signaling network. J Biol Chem. 2011 Mar 25;286(12):9897-904. Epub 2011 Jan 21. PMID:21257757 doi:10.1074/jbc.R110.174268
- ↑ Yamashita A, Maeda K, Maeda Y. Crystal structure of CapZ: structural basis for actin filament barbed end capping. EMBO J. 2003 Apr 1;22(7):1529-38. PMID:12660160 doi:10.1093/emboj/cdg167
- ↑ dos Remedios CG, Chhabra D, Kekic M, Dedova IV, Tsubakihara M, Berry DA, Nosworthy NJ. Actin binding proteins: regulation of cytoskeletal microfilaments. Physiol Rev. 2003 Apr;83(2):433-73. PMID:12663865 doi:10.1152/physrev.00026.2002
- ↑ Narita A, Takeda S, Yamashita A, Maeda Y. Structural basis of actin filament capping at the barbed-end: a cryo-electron microscopy study. EMBO J. 2006 Nov 29;25(23):5626-33. Epub 2006 Nov 16. PMID:17110933 doi:10.1038/sj.emboj.7601395