Download MendeleyCrystal structure of the C-terminal four-helix bundle of the potassium channel KCa3.1.
Ji, T., Corbalan-Garcia, S., Hubbard, S.R.(2018) PLoS One 13: e0199942-e0199942
- PubMed: 29953543
- DOI: https://doi.org/10.1371/journal.pone.0199942
- Primary Citation of Related Structures:
6D42 - PubMed Abstract:
KCa3.1 (also known as SK4 or IK1) is a mammalian intermediate-conductance potassium channel that plays a critical role in the activation of T cells, B cells, and mast cells, effluxing potassium ions to maintain a negative membrane potential for influxing calcium ions. KCa3.1 shares primary sequence similarity with three other (low-conductance) potassium channels: KCa2.1, KCa2.2, and KCa2.3 (also known as SK1-3). These four homotetrameric channels bind calmodulin (CaM) in the cytoplasmic region, and calcium binding to CaM triggers channel activation. Unique to KCa3.1, activation also requires phosphorylation of a single histidine residue, His358, in the cytoplasmic region, which relieves copper-mediated inhibition of the channel. Near the cytoplasmic C-terminus of KCa3.1 (and KCa2.1-2.3), secondary-structure analysis predicts the presence of a coiled-coil/heptad repeat. Here, we report the crystal structure of the C-terminal coiled-coil region of KCa3.1, which forms a parallel four-helix bundle, consistent with the tetrameric nature of the channel. Interestingly, the four copies of a histidine residue, His389, in an 'a' position within the heptad repeat, are observed to bind a copper ion along the four-fold axis of the bundle. These results suggest that His358, the inhibitory histidine in KCa3.1, might coordinate a copper ion through a similar binding mode.
Organizational Affiliation:
Kimmel Center for Biology and Medicine of the Skirball Institute, Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, NY, United States of America.
