Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, Canada.
Am J Physiol Cell Physiol. 2010 May;298(5):C1066-76. doi: 10.1152/ajpcell.00389.2009. Epub 2010 Feb 3.
All four mammalian hyperpolarization-activated cyclic nucleotide-modulated (HCN) channel isoforms have been shown to undergo N-linked glycosylation in the brain. With the mouse HCN2 isoform as a prototype, HCN channels have further been suggested to require N-glycosylation for function, a provocative finding that would make them unique in the voltage-gated potassium channel superfamily. Here, we show that both the HCN1 and HCN2 isoforms are also predominantly N-glycosylated in the embryonic heart, where they are found in significant amounts and where HCN-mediated currents are known to regulate beating frequency. Surprisingly, we find that N-glycosylation is not required for HCN2 function, although its cell surface expression is highly dependent on the presence of N-glycans. Comparatively, disruption of N-glycosylation only modestly impacts cell surface expression of HCN1 and leaves permeation and gating functions almost unchanged. This difference between HCN1 and HCN2 is consistent with evolutionary trajectories that diverged in an isoform-specific manner after gene duplication from a common HCN ancestor that lacked N-glycosylation and was able to localize efficiently to the cell surface.
所有四种哺乳动物超极化激活环核苷酸调节（HCN）通道同工型都已被证明在大脑中发生 N 连接糖基化。以小鼠 HCN2 同工型为原型，HCN 通道进一步被认为需要 N-糖基化才能发挥功能，这一挑衅性的发现使它们在电压门控钾通道超家族中独一无二。在这里，我们表明 HCN1 和 HCN2 同工型在胚胎心脏中也主要是 N 连接糖基化的，在那里它们以大量存在，并且已知 HCN 介导的电流调节跳动频率。令人惊讶的是，我们发现 N-糖基化不是 HCN2 功能所必需的，尽管其细胞表面表达高度依赖于 N-聚糖的存在。相比之下，破坏 N-糖基化仅适度影响 HCN1 的细胞表面表达，并使渗透和门控功能几乎不变。HCN1 和 HCN2 之间的这种差异与进化轨迹一致，这些轨迹在基因复制后以特定于同工型的方式发散，从缺乏 N-糖基化并且能够有效地定位于细胞表面的共同 HCN 祖先开始。
