Weitz D, Zoche M, Müller F, Beyermann M, Körschen H G, Kaupp U B, Koch K W
Institut für Biologische Informationsverarbeitung, Forschungszentrum Jülich, D-52425 Jülich.
EMBO J. 1998 Apr 15;17(8):2273-84. doi: 10.1093/emboj/17.8.2273.
Calmodulin (CaM) controls the activity of the rod cGMP-gated ion channel by decreasing the apparent cGMP affinity. We have examined the mechanism of this modulation using electrophysiological and biochemical techniques. Heteromeric channels, consisting of alpha- and beta-subunits, display a high CaM sensitivity (EC50 </=5 nM) similar to the native channel. Using surface plasmon resonance spectroscopy, we identified two unconventional CaM-binding sites (CaM1 and CaM2), one in each of the N- and the C-terminal regions of the beta-subunit. Ca2+ co-operatively stimulates binding of CaM to these sites exactly within the range of [Ca2+] occurring during a light response. Deletion of the N-terminal CaM1 site results in channels that are no longer CaM-sensitive, whereas deletion of CaM2 has only minor effects. We discuss different models to explain the high-affinity binding of CaM.
钙调蛋白（CaM）通过降低视杆细胞环磷酸鸟苷（cGMP）门控离子通道的表观cGMP亲和力来控制其活性。我们使用电生理和生化技术研究了这种调节机制。由α亚基和β亚基组成的异源通道表现出与天然通道相似的高CaM敏感性（半数有效浓度[EC50]≤5 nM）。利用表面等离子体共振光谱，我们在β亚基的N端和C端区域分别鉴定出两个非常规的CaM结合位点（CaM1和CaM2）。Ca2+协同刺激CaM与这些位点的结合，其浓度范围恰好与光反应期间出现的[Ca2+]范围一致。删除N端的CaM1位点会导致通道不再对CaM敏感，而删除CaM2位点只有轻微影响。我们讨论了不同模型来解释CaM的高亲和力结合。
