Reusch R N, Huang R, Bramble L L
Department of Microbiology, Michigan State University, East Lansing 48824, USA.
Biophys J. 1995 Sep;69(3):754-66. doi: 10.1016/S0006-3495(95)79958-1.
The lipidic polymer, poly-3-hydroxybutyrate (PHB), is found in the plasma membranes of Escherichia col complexed to calcium polyphosphate (CaPPi). The composition, location, and putative structure of the polymer salt complexes led Reusch and Sadoff (1988) to propose that the complexes function as Ca2+ channels. Here we use bilayer patch-clamp techniques to demonstrate that voltage-activated Ca2+ channels composed of PHB and CaPPi are in the plasma membranes of E. coli. Single channel calcium currents were observed in vesicles of plasma membranes incorporated into planar bilayers of synthetic 1-palmitoyl, 2-oleoyl phosphatidylcholine. The channels were extracted from cells and incorporated into bilayers, where they displayed many of the signal characteristics of protein Ca2+ channels: voltage-activated selective for divalent over monovalent cations, permeant to Ca2+, manner by La3+, Co2+, Cd2+, and Mg2+, in that order. The channel-active extract, purified by size exclusion chromatography, was found to contain only PHB and CaPPi. This composition was confirmed by the observation of comparable single channel currents with complexes reconstituted from synthetic CaPPi and PHB, isolated from E. coli. This is the first report of a biological non-proteinaceous calcium channel. We suggest that poly-3-hydroxybutyrate/calcium polyphosphate complexes are evolutionary antecedents of protein Ca2+ channels.
脂质聚合物聚-3-羟基丁酸酯（PHB）存在于大肠杆菌的质膜中，与多聚磷酸钙（CaPPi）复合。聚合物盐复合物的组成、位置和假定结构促使Reusch和Sadoff（1988年）提出该复合物起着Ca2+通道的作用。在此，我们使用双层膜片钳技术来证明由PHB和CaPPi组成的电压激活Ca2+通道存在于大肠杆菌的质膜中。在掺入合成1-棕榈酰、2-油酰磷脂酰胆碱平面双层膜的质膜囊泡中观察到单通道钙电流。这些通道从细胞中提取并掺入双层膜中，在那里它们表现出许多蛋白质Ca2+通道的信号特征：电压激活，对二价阳离子比对一价阳离子有选择性，对Ca2+有通透性，依次被La3+、Co2+、Cd2+和Mg2+阻断。通过尺寸排阻色谱法纯化的通道活性提取物被发现只含有PHB和CaPPi。用从大肠杆菌中分离出的合成CaPPi和PHB重构的复合物观察到可比的单通道电流，证实了这种组成。这是关于生物非蛋白质钙通道的首次报道。我们认为聚-3-羟基丁酸酯/多聚磷酸钙复合物是蛋白质Ca2+通道的进化前身。
