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Disruption of the IS6-AID linker affects voltage-gated calcium channel inactivation and facilitation.

Findeisen F, Minor DL - J. Gen. Physiol. (2009)

Bottom Line: The Ca(V)beta/Ca(V)alpha(1)-I-II loop and Ca(2+)/calmodulin (CaM)/Ca(V)alpha(1)-C-terminal tail complexes have been shown to modulate each, respectively.Nevertheless, how each complex couples to the pore and whether each affects inactivation independently have remained unresolved.Collectively, the data strongly suggest that components traditionally associated solely with VDI, Ca(V)beta and the IS6-AID linker, are essential for calcium-dependent modulation, and that both Ca(V)beta-dependent and CaM-dependent components couple to the pore by a common mechanism requiring Ca(V)beta and an intact IS6-AID linker.

View Article: PubMed Central - PubMed

Affiliation: Cardiovascular Research Institute, Department of Biochemistry and Biophysics, California Institute for Quantitative Biosciences, University of California, San Francisco, CA 94158, USA.

ABSTRACT
Two processes dominate voltage-gated calcium channel (Ca(V)) inactivation: voltage-dependent inactivation (VDI) and calcium-dependent inactivation (CDI). The Ca(V)beta/Ca(V)alpha(1)-I-II loop and Ca(2+)/calmodulin (CaM)/Ca(V)alpha(1)-C-terminal tail complexes have been shown to modulate each, respectively. Nevertheless, how each complex couples to the pore and whether each affects inactivation independently have remained unresolved. Here, we demonstrate that the IS6-alpha-interaction domain (AID) linker provides a rigid connection between the pore and Ca(V)beta/I-II loop complex by showing that IS6-AID linker polyglycine mutations accelerate Ca(V)1.2 (L-type) and Ca(V)2.1 (P/Q-type) VDI. Remarkably, mutations that either break the rigid IS6-AID linker connection or disrupt Ca(V)beta/I-II association sharply decelerate CDI and reduce a second Ca(2+)/CaM/Ca(V)alpha(1)-C-terminal-mediated process known as calcium-dependent facilitation. Collectively, the data strongly suggest that components traditionally associated solely with VDI, Ca(V)beta and the IS6-AID linker, are essential for calcium-dependent modulation, and that both Ca(V)beta-dependent and CaM-dependent components couple to the pore by a common mechanism requiring Ca(V)beta and an intact IS6-AID linker.

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Cartoon model of a CaV channel. Based on the likely gross similarly between CaV and Kv transmembrane portions, the Kv1.2 transmembrane domains (gray surface; PDB accession no. 2A79) are used to represent the CaV transmembrane domains. The IS6-AID linker (red) was modeled manually by building a helix of corresponding length between the Kv1.2 S6 helix C terminus (dark gray) and AID helix (light gray) from the CaVβ2a–AID complex (PDB accession no. 1T0J). The CaVβ2a–AID complex is shown as follows: green, SH3 domain; light blue, NK domain; light gray, AID. N-terminal CaVβ2a variable segment, V1, of unknown structure, is shown anchored to the membrane via N-terminal palmitoylation, and the V2 loop is indicated. Arrow along the IS6-AID linker indicates communication between CaVβ and the pore domain. This is lost in the multiple glycine mutants (bottom) and affects VDI, CDI, and CDF. Curved arrow between the Ca2+/CaM-IQ domain complex (PDB accession no. 2BE6), Ca2+/CaM (dark blue), and IQ helix (gray) represents the functional interaction between the C-terminal tail complex and the CaVβ2a–AID complex required for CDI and CDF. In CaV1.2 GGG (bottom), IS6-AID helix disruption blunts the influence of the Ca2+/CaM-IQ domain on the transmembrane pore.
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fig7: Cartoon model of a CaV channel. Based on the likely gross similarly between CaV and Kv transmembrane portions, the Kv1.2 transmembrane domains (gray surface; PDB accession no. 2A79) are used to represent the CaV transmembrane domains. The IS6-AID linker (red) was modeled manually by building a helix of corresponding length between the Kv1.2 S6 helix C terminus (dark gray) and AID helix (light gray) from the CaVβ2a–AID complex (PDB accession no. 1T0J). The CaVβ2a–AID complex is shown as follows: green, SH3 domain; light blue, NK domain; light gray, AID. N-terminal CaVβ2a variable segment, V1, of unknown structure, is shown anchored to the membrane via N-terminal palmitoylation, and the V2 loop is indicated. Arrow along the IS6-AID linker indicates communication between CaVβ and the pore domain. This is lost in the multiple glycine mutants (bottom) and affects VDI, CDI, and CDF. Curved arrow between the Ca2+/CaM-IQ domain complex (PDB accession no. 2BE6), Ca2+/CaM (dark blue), and IQ helix (gray) represents the functional interaction between the C-terminal tail complex and the CaVβ2a–AID complex required for CDI and CDF. In CaV1.2 GGG (bottom), IS6-AID helix disruption blunts the influence of the Ca2+/CaM-IQ domain on the transmembrane pore.

Mentions: Our experiments testing the importance of the structural integrity of the IS6-AID linker support the idea that in CaV1 and CaV2 channels, the IS6-AID linker is a helix that functions as a rigid rod connecting CaVβ to the pore domain (Opatowsky et al., 2004; Van Petegem et al., 2004; Arias et al., 2005) (Fig. 7 A). This structural connection appears to be responsible for a large fraction of the VDI modulation that any CaVβ isoform imparts on CaVα1 subunits and for the effects CaVβ has on channel activation (compare Figs. 1 and 4).


Disruption of the IS6-AID linker affects voltage-gated calcium channel inactivation and facilitation.

Findeisen F, Minor DL - J. Gen. Physiol. (2009)

Cartoon model of a CaV channel. Based on the likely gross similarly between CaV and Kv transmembrane portions, the Kv1.2 transmembrane domains (gray surface; PDB accession no. 2A79) are used to represent the CaV transmembrane domains. The IS6-AID linker (red) was modeled manually by building a helix of corresponding length between the Kv1.2 S6 helix C terminus (dark gray) and AID helix (light gray) from the CaVβ2a–AID complex (PDB accession no. 1T0J). The CaVβ2a–AID complex is shown as follows: green, SH3 domain; light blue, NK domain; light gray, AID. N-terminal CaVβ2a variable segment, V1, of unknown structure, is shown anchored to the membrane via N-terminal palmitoylation, and the V2 loop is indicated. Arrow along the IS6-AID linker indicates communication between CaVβ and the pore domain. This is lost in the multiple glycine mutants (bottom) and affects VDI, CDI, and CDF. Curved arrow between the Ca2+/CaM-IQ domain complex (PDB accession no. 2BE6), Ca2+/CaM (dark blue), and IQ helix (gray) represents the functional interaction between the C-terminal tail complex and the CaVβ2a–AID complex required for CDI and CDF. In CaV1.2 GGG (bottom), IS6-AID helix disruption blunts the influence of the Ca2+/CaM-IQ domain on the transmembrane pore.
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2654080&req=5

fig7: Cartoon model of a CaV channel. Based on the likely gross similarly between CaV and Kv transmembrane portions, the Kv1.2 transmembrane domains (gray surface; PDB accession no. 2A79) are used to represent the CaV transmembrane domains. The IS6-AID linker (red) was modeled manually by building a helix of corresponding length between the Kv1.2 S6 helix C terminus (dark gray) and AID helix (light gray) from the CaVβ2a–AID complex (PDB accession no. 1T0J). The CaVβ2a–AID complex is shown as follows: green, SH3 domain; light blue, NK domain; light gray, AID. N-terminal CaVβ2a variable segment, V1, of unknown structure, is shown anchored to the membrane via N-terminal palmitoylation, and the V2 loop is indicated. Arrow along the IS6-AID linker indicates communication between CaVβ and the pore domain. This is lost in the multiple glycine mutants (bottom) and affects VDI, CDI, and CDF. Curved arrow between the Ca2+/CaM-IQ domain complex (PDB accession no. 2BE6), Ca2+/CaM (dark blue), and IQ helix (gray) represents the functional interaction between the C-terminal tail complex and the CaVβ2a–AID complex required for CDI and CDF. In CaV1.2 GGG (bottom), IS6-AID helix disruption blunts the influence of the Ca2+/CaM-IQ domain on the transmembrane pore.
Mentions: Our experiments testing the importance of the structural integrity of the IS6-AID linker support the idea that in CaV1 and CaV2 channels, the IS6-AID linker is a helix that functions as a rigid rod connecting CaVβ to the pore domain (Opatowsky et al., 2004; Van Petegem et al., 2004; Arias et al., 2005) (Fig. 7 A). This structural connection appears to be responsible for a large fraction of the VDI modulation that any CaVβ isoform imparts on CaVα1 subunits and for the effects CaVβ has on channel activation (compare Figs. 1 and 4).

Bottom Line: The Ca(V)beta/Ca(V)alpha(1)-I-II loop and Ca(2+)/calmodulin (CaM)/Ca(V)alpha(1)-C-terminal tail complexes have been shown to modulate each, respectively.Nevertheless, how each complex couples to the pore and whether each affects inactivation independently have remained unresolved.Collectively, the data strongly suggest that components traditionally associated solely with VDI, Ca(V)beta and the IS6-AID linker, are essential for calcium-dependent modulation, and that both Ca(V)beta-dependent and CaM-dependent components couple to the pore by a common mechanism requiring Ca(V)beta and an intact IS6-AID linker.

View Article: PubMed Central - PubMed

Affiliation: Cardiovascular Research Institute, Department of Biochemistry and Biophysics, California Institute for Quantitative Biosciences, University of California, San Francisco, CA 94158, USA.

ABSTRACT
Two processes dominate voltage-gated calcium channel (Ca(V)) inactivation: voltage-dependent inactivation (VDI) and calcium-dependent inactivation (CDI). The Ca(V)beta/Ca(V)alpha(1)-I-II loop and Ca(2+)/calmodulin (CaM)/Ca(V)alpha(1)-C-terminal tail complexes have been shown to modulate each, respectively. Nevertheless, how each complex couples to the pore and whether each affects inactivation independently have remained unresolved. Here, we demonstrate that the IS6-alpha-interaction domain (AID) linker provides a rigid connection between the pore and Ca(V)beta/I-II loop complex by showing that IS6-AID linker polyglycine mutations accelerate Ca(V)1.2 (L-type) and Ca(V)2.1 (P/Q-type) VDI. Remarkably, mutations that either break the rigid IS6-AID linker connection or disrupt Ca(V)beta/I-II association sharply decelerate CDI and reduce a second Ca(2+)/CaM/Ca(V)alpha(1)-C-terminal-mediated process known as calcium-dependent facilitation. Collectively, the data strongly suggest that components traditionally associated solely with VDI, Ca(V)beta and the IS6-AID linker, are essential for calcium-dependent modulation, and that both Ca(V)beta-dependent and CaM-dependent components couple to the pore by a common mechanism requiring Ca(V)beta and an intact IS6-AID linker.

Show MeSH
Related in: MedlinePlus