Reusch R N, Sadoff H L
Department of Microbiology and Public Health, Michigan State University, East Lansing 48824.
Proc Natl Acad Sci U S A. 1988 Jun;85(12):4176-80. doi: 10.1073/pnas.85.12.4176.
A poly-beta-hydroxybutyrate complex extracted from the plasma membranes of genetically competent Escherichia coli contained polyhydroxybutyrate:polyphosphate:calcium in molar ratios approximating 1:1:0.5. The chain length of the polyhydroxybutyrate was estimated as 120-200 subunits, and that of the polyphosphate was estimated as 130-170 subunits. The extracted complex, when incorporated into liposomes, exhibited a lipid phase transition in the same temperature range as that of the membrane complex in whole cells as well as the same properties of irreversibility, lability, and sensitivity to chelating buffers. Space-filling molecular models and molecular energy minimization methods (Charmm) were used to develop and evaluate a plausible structure for the complex. It is proposed that the polyhydroxybutyrate forms an exolipophilic-endopolarophilic helix around an inner framework helix of calcium polyphosphate. The calcium ions link the two polymers by forming ionic bonds with phosphoryl oxygens of the polyphosphate and ion-dipole bonds with the ester carbonyl oxygens of the polyhydroxybutyrate. This symmetrical structure forms a channel through the membrane and may play a role in the transport of calcium, phosphate, and DNA.
从具有遗传感受态的大肠杆菌质膜中提取的聚-β-羟基丁酸酯复合物含有聚羟基丁酸酯：聚磷酸盐：钙，其摩尔比约为1:1:0.5。聚羟基丁酸酯的链长估计为120 - 200个亚基，聚磷酸盐的链长估计为130 - 170个亚基。提取的复合物掺入脂质体后，在与全细胞膜复合物相同的温度范围内表现出脂质相变，以及相同的不可逆性、不稳定性和对螯合缓冲液的敏感性。使用空间填充分子模型和分子能量最小化方法（Charmm）来开发和评估该复合物的合理结构。有人提出，聚羟基丁酸酯围绕聚磷酸钙的内部骨架螺旋形成一个外亲脂性 - 内亲极性螺旋。钙离子通过与聚磷酸盐的磷酰氧形成离子键以及与聚羟基丁酸酯的酯羰基氧形成离子 - 偶极键来连接这两种聚合物。这种对称结构形成了一个穿过膜的通道，可能在钙、磷酸盐和DNA的运输中起作用。
