Chemistry Department, Carnegie Mellon University, 4400 Fifth Ave., Pittsburgh, PA, 15213, USA.
Department of Biochemistry and Molecular Biophysics, Columbia University, 650 West 168th St., New York, NY, 10032, USA.
Sci Rep. 2018 Apr 9;8(1):5715. doi: 10.1038/s41598-018-23972-5.
Calcium is the most abundant metal in the human body that plays vital roles as a cellular electrolyte as well as the smallest and most frequently used signaling molecule. Calcium uptake in epithelial tissues is mediated by tetrameric calcium-selective transient receptor potential (TRP) channels TRPV6 that are implicated in a variety of human diseases, including numerous forms of cancer. We used TRPV6 crystal structures as templates for molecular dynamics simulations to identify ion binding sites and to study the permeation mechanism of calcium and other ions through TRPV6 channels. We found that at low Ca concentrations, a single calcium ion binds at the selectivity filter narrow constriction formed by aspartates D541 and allows Na permeation. In the presence of ions, no water binds to or crosses the pore constriction. At high Ca concentrations, calcium permeates the pore according to the knock-off mechanism that includes formation of a short-lived transition state with three calcium ions bound near D541. For Ba, the transition state lives longer and the knock-off permeation occurs slower. Gd binds at D541 tightly, blocks the channel and prevents Na from permeating the pore. Our results provide structural foundations for understanding permeation and block in tetrameric calcium-selective ion channels.
钙是人体中含量最丰富的金属，作为细胞电解质以及最小、最常用的信号分子发挥着重要作用。上皮组织中的钙摄取由四聚体钙选择性瞬时受体电位 (TRP) 通道 TRPV6 介导，该通道与多种人类疾病有关，包括多种形式的癌症。我们使用 TRPV6 晶体结构作为分子动力学模拟的模板，以确定离子结合位点，并研究钙和其他离子通过 TRPV6 通道的渗透机制。我们发现，在低 Ca 浓度下，单个钙离子结合在由天冬氨酸 D541 形成的选择性过滤器狭窄缩窄处，允许 Na 渗透。在存在离子的情况下，没有水分子结合或穿过孔道狭窄处。在高 Ca 浓度下，钙根据敲除机制渗透孔道，该机制包括形成一个短暂的过渡态，其中三个钙离子结合在 D541 附近。对于 Ba，过渡态的寿命更长，敲除渗透发生得更慢。Gd 与 D541 紧密结合，阻断通道并防止 Na 渗透过孔道。我们的结果为理解四聚体钙选择性离子通道的渗透和阻断提供了结构基础。
