Centre for Integrative Physiology, College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh, EH8 9XD, Scotland.
J Biol Chem. 2012 Apr 27;287(18):14718-25. doi: 10.1074/jbc.M111.335547. Epub 2012 Mar 7.
Protein palmitoylation is rapidly emerging as an important determinant in the regulation of ion channels, including large conductance calcium-activated potassium (BK) channels. However, the enzymes that control channel palmitoylation are largely unknown. Indeed, although palmitoylation is the only reversible lipid modification of proteins, acyl thioesterases that control ion channel depalmitoylation have not been identified. Here, we demonstrate that palmitoylation of the intracellular S0-S1 loop of BK channels is controlled by two of the 23 mammalian palmitoyl-transferases, zDHHC22 and zDHHC23. Palmitoylation by these acyl transferases is essential for efficient cell surface expression of BK channels. In contrast, depalmitoylation is controlled by the cytosolic thioesterase APT1 (LYPLA1), but not APT2 (LYPLA2). In addition, we identify a splice variant of LYPLAL1, a homolog with ∼30% identity to APT1, that also controls BK channel depalmitoylation. Thus, both palmitoyl acyltransferases and acyl thioesterases display discrete substrate specificity for BK channels. Because depalmitoylated BK channels are retarded in the trans-Golgi network, reversible protein palmitoylation provides a critical checkpoint to regulate exit from the trans-Golgi network and thus control BK channel cell surface expression.
蛋白质棕榈酰化作为调节离子通道（包括大电导钙激活钾（BK）通道）的重要决定因素正在迅速出现。然而，控制通道棕榈酰化的酶在很大程度上是未知的。事实上，尽管棕榈酰化是蛋白质唯一的可逆脂质修饰，但控制离子通道去棕榈酰化的酰基辅酶 A 水解酶尚未被鉴定。在这里，我们证明了 BK 通道细胞内 S0-S1 环的棕榈酰化由 23 种哺乳动物棕榈酰转移酶中的两种，即 zDHHC22 和 zDHHC23 控制。这些酰基转移酶的棕榈酰化对于 BK 通道的有效细胞表面表达是必需的。相比之下，去棕榈酰化由胞质硫酯酶 APT1（LYPLA1）控制，但不由 APT2（LYPLA2）控制。此外，我们鉴定了 LYPLA1 的剪接变体，它与 APT1 的同源性约为 30%，也控制 BK 通道的去棕榈酰化。因此，棕榈酰酰基转移酶和酰基辅酶 A 水解酶都显示出对 BK 通道的独特底物特异性。由于去棕榈酰化的 BK 通道在高尔基体内网中受到阻滞，可逆的蛋白质棕榈酰化提供了一个关键的检查点，以调节从高尔基体内网的出口，从而控制 BK 通道的细胞表面表达。
