Delineation of a LRR family of BK channel auxiliary subunits

描述(申请人提供)：大电导、钙和电压激活钾(BK)通道是钾通道家族中唯一的成员，它具有最大的单通道电导，并由电压和胞内游离钙([Ca2+]i)双重激活，由成孔、电压和钙敏感亚基(BK)组成，可单独或与组织特异性调节亚基(1-4)结合。BK通道通常很难开放，在体内需要一致的膜去极化和[Ca~(2+)]i升高才能激活。然而，利用蛋白质组学和电生理学方法，我们最近发现了一个新的BK通道辅助亚单位，富含亮氨酸的重复序列(LRR)，它含有膜蛋白LRRC26，它导致电压依赖性的前所未有的大负移(~-150 mV)，使BK通道在甚至接近静止电压和钙水平的可兴奋和不可兴奋细胞中激活。LRRC26代表一个新的BK通道辅助亚基家族，在结构上与已知的四个亚基不同，命名为α-亚基。就像存在多个具有不同调制功能的组织特异性BK通道亚基一样，我们假设存在LRRC26样亚单位的其他成员，它们在广泛的不同细胞类型上对BK通道进行差异调制。为了确定BK通道亚基的结构和功能特征，我们设计了以下两个特定的目标：1)鉴定和鉴定BK通道亚基的新成员；2)鉴定BK通道亚基调节功能的结构决定因素。我们从蛋白质数据库中鉴定了5个LRRC26同源基因：LRRC38、LRRC52、LRRC55、LRTM1和LRTM2。实验旨在确定这些LRRC26类似物对BK通道功能的调制作用，并确定导致LRR蛋白成为BK通道调制器的关键结构元件。总体而言，本研究旨在确定新的家族成员，并确定BK通道亚基的结构和功能特征。这些研究结果可能会建立一个广泛的离子通道辅助亚基LRR家族，深入了解LRRC26‘S在BK通道调节中的独特能力，并为BK通道相关疾病的治疗和药物开发提供新的蛋白质靶点。

DESCRIPTION (provided by applicant): Large conductance, calcium and voltage-activated potassium (BK) channel is a unique member of potassium channel family, which has the largest single channel conductance and is dually activated by voltage and cytosolic free Ca2+ ([Ca2+]i), consisting of the pore-forming, voltage and Ca2+-sensing -subunits (BK) either alone or in association with tissue specific regulatory -subunits (1 - 4). BK channels are generally hard to open, requiring coincident membrane depolarization and [Ca2+]i rise for activation in vivo. However, with proteomic and electrophysiological approaches, we have recently identified a novel BK channel auxiliary subunit, leucine-rich repeat (LRR) containing membrane protein LRRC26 that causes an unprecedented large negative shift (~ -150 mV) in voltage dependence, allowing BK channel activation at even near resting voltages and calcium levels in excitable and non-excitable cells. LRRC26 represents a new family of BK channel auxiliary subunits, which is structurally distinct from the four known -subunits and designated as a -subunit. Like the presence of multiple tissue specific BK channel -subunits with different modulatory functions, we hypothesized that there exist other members of the LRRC26-like -subunits, which differentially modulate BK channels over a wide range of different cell types. The following two specific aims are designed to delineate the family members and to define the structural and functional features of the BK channel -subunits: 1) Identify and characterize new members of BK channel -subunits; 2) identify the structural determinants for modulatory function of the BK channel -subunits. We have identified five LRRC26 paralogs, LRRC38, LRRC52, LRRC55, LRTM1 and LRTM2, from protein database. Experiments are designed to determine the modulatory effects of these LRRC26 paralogs on BK channel function, and to identify key structural elements responsible for a LRR protein to be a BK channel modulator. Overall, the proposed research is designed to identify new family members and to define the structural and functional features of the BK channel -subunits. The findings from the proposed research may establish a broad LRR family of ion channel auxiliary subunits, gain an in-depth understanding of the LRRC26's unique capacity in BK channel modulation, and provide new protein targets for BK channel related disease treatment and drug development.