Species-specific differences among KCNMB3 BK β3 auxiliary subunits:: Some β3 N-terminal variants may be primate-specific subunits
Species-specific differences among KCNMB3 BK β3 auxiliary subunits:: Some β3 N-terminal variants may be primate-specific subunits
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DOI：
10.1085/jgp.200809969
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发表时间：
2008-07-01
影响因子：
3.8
通讯作者：
Lingle, Christopher J.
中科院分区：
文献类型：
--
作者：
Zeng, Xuhui;Xia, Xiao-Ming;Lingle, Christopher J.
KCNMB3 基因编码哺乳动物基因组中发现的四个辅助 β 亚基家族之一，这些亚基与 Slo1 α 亚基相关并调节 BK 通道功能。在人类中，KCNMB3 基因包含四个 N 末端替代外显子，可产生四个功能不同的 β 3 亚基，即 β 3a-d。三种变体，β 3a-c，表现出动力学上不同的失活行为。由于 BK 辅助亚基的生理作用的研究将取决于啮齿类动物的研究，因此我们在这里确定了小鼠 β 3 变体的身份和功能特性。小鼠和人类之间的 β 1、β 2 和 β 4 亚基表现出 83.2%、95.3% 和 93.8% 的同一性，而小鼠 β 3 亚基（不包括 N 末端剪接变体）与人类对应物仅具有 62.8% 的氨基酸同一性。基于对小鼠基因组的检查和对小鼠 cDNA 文库的筛选，我们在人类中发现的四种 N 末端候选物中仅鉴定了两种 N 末端候选物：β 3a 和 β 3b。人类和小鼠 β 3a 亚基都会产生特征性的使用依赖性失活。令人惊讶的是，虽然 h beta 3b 表现出快速失活，但推定的 m beta 3b 却没有失活。此外，与 h beta 3 不同，m beta 3 亚基无论 N 末端如何，都会在给定的 Ca(2+) 浓度下介导门控向更负电势的转变。斑块切除后，门控的转变逐渐消失，表明门控转变涉及一些依赖于细胞质环境的调节过程。检查其他基因组以评估剪接变体之间的保守性表明，假定的 m beta 3b N 末端可能不是 h beta 3b N 末端的真正直系同源物，并且 beta 3c 和 beta 3d 似乎都可能是灵长类动物特异性 N 末端变体。这些结果具有三个关键意义：首先，同源β3亚基的功能特性在哺乳动物物种之间可能有所不同；其次，同源β3亚基的具体生理作用在哺乳动物物种之间可能有所不同；第三，一些β3变体可能是灵长类特异性通道亚基。
The KCNMB3 gene encodes one of a family of four auxiliary beta subunits found in the mammalian genome that associate with Slo1 alpha subunits and regulate BK channel function. In humans, the KCNMB3 gene contains four N-terminal alternative exons that produce four functionally distinct beta 3 subunits, beta 3a-d. Three variants, beta 3a-c, exhibit kinetically distinct inactivation behaviors. Since investigation of the physiological roles of BK auxiliary subunits will depend on studies in rodents, here we have determined the identity and functional properties of mouse beta 3 variants. Whereas beta 1, beta 2, and beta 4 subunits exhibit 83.2%, 95.3%, and 93.8% identity between mouse and human, the mouse beta 3 subunit, excluding N-terminal splice variants, shares only 62.8% amino acid identity with its human counterpart. Based on an examination of the mouse genome and screening of mouse cDNA libraries, here we have identified only two N-terminal candidates, beta 3a and beta 3b, of the four found in humans. Both human and mouse beta 3a subunits produce a characteristic use-dependent inactivation. Surprisingly, whereas the h beta 3b exhibits rapid inactivation, the putative m beta 3b does not inactivate. Furthermore, unlike h beta 3, the m beta 3 subunit, irrespective of the N terminus, mediates a shift in gating to more negative potentials at a given Ca(2+) concentration. The shift in gating gradually is lost following patch excision, suggesting that the gating shift involves some regulatory process dependent on the cytosolic milieu. Examination of additional genomes to assess conservation among splice variants suggests that the putative m beta 3b N terminus may not be a true orthologue of the h beta 3b N terminus and that both beta 3c and beta 3d appear likely to be primate-specific N-terminal variants. These results have three key implications: first, functional properties of homologous beta 3 subunits may differ among mammalian species; second, the specific physiological roles of homologous beta 3 subunits may differ among mammalian species; and, third, some beta 3 variants may be primate-specificion channel subunits.