Structures of CaV2 Ca2+/CaM-IQ Domain Complexes Reveal Binding Modes that Underlie Calcium-Dependent Inactivation and Facilitation

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Abstract

Calcium influx drives two opposing voltage-activated calcium channel (CaV) self-modulatory processes: calcium-dependent inactivation (CDI) and calcium-dependent facilitation (CDF). Specific Ca2+/calmodulin (Ca2+/CaM) lobes produce CDI and CDF through interactions with the CaVα1 subunit IQ domain. Curiously, Ca2+/CaM lobe modulation polarity appears inverted between CaV1s and CaV2s. Here, we present crystal structures of CaV2.1, CaV2.2, and CaV2.3 Ca2+/CaM-IQ domain complexes. All display binding orientations opposite to CaV1.2 with a physical reversal of the CaM lobe positions relative to the IQ α-helix. Titration calorimetry reveals lobe competition for a high-affinity site common to CaV1 and CaV2 IQ domains that is occupied by the CDI lobe in the structures. Electrophysiological experiments demonstrate that the N-terminal CaV2 Ca2+/C-lobe anchors affect CDF. Together, the data unveil the remarkable structural plasticity at the heart of CaV feedback modulation and indicate that CaV1 and CaV2 IQ domains bear a dedicated CDF site that exchanges Ca2+/CaM lobe occupants. © 2008 Elsevier Ltd. All rights reserved.

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Kim, E. Y., Rumpf, C. H., Fujiwara, Y., Cooley, E. S., Van Petegem, F., & Minor, D. L. (2008). Structures of CaV2 Ca2+/CaM-IQ Domain Complexes Reveal Binding Modes that Underlie Calcium-Dependent Inactivation and Facilitation. Structure, 16(10), 1455–1467. https://doi.org/10.1016/j.str.2008.07.010

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