Poly (3-Hydroxybutyrate)/Polyphosphate Ion Channels

离子通道是膜上的大分子孔，允许选定的离子通过脂质双层进行转移。这些通道大多由蛋白质或多肽组成。然而，在革兰氏阴性和革兰氏阳性细菌中发现了由两个简单的线性均聚物(聚(3-羟基丁酸酯)和无机聚磷酸盐)组成的非蛋白质钙选择通道。这两种聚合物都是原核和真核细胞中普遍存在的成分，都具有与离子传导相关的独特的物理化学性质。这两种聚合物在体外结合在脂质双层中形成通道，表现出电压激活的电导，对一价阳离子上的二价阳离子具有选择性，对钙、锶和钡具有选择性，并被过渡金属阳离子阻断。这些研究将确定导致这些特性的结构决定因素和基本分子机制。从细菌中分离或人工制备的聚合物组分将被掺入脂质双层中，并将在不同的定义条件下通过电压钳技术检测单通道电流。研究旨在确定影响双层流动性的因素如何影响电导、磁导、选择性和电压门控。其他研究将确定pH对阳离子选择性的影响，镁和其他阳离子阻止钙电导的方式，以及已知为蛋白质钙通道激动剂和拮抗剂的可能影响。这些对一个简单但明显普遍存在的原核生物通道的研究应该会为离子跨双分子层转移的一般机制提供见解。这些钙通道可能是真核生物蛋白质钙通道进化过程中的先驱--“极简”钙通道的模型。

Ion channels are macromolecular pores in membranes that permit transfer of selected ions through the lipid bilayer. Most of these channels are composed of proteins or peptides. However, a non-proteinaceous calcium-selective channel, composed of two simple linear homopolymers (poly(3-hydroxybutyrate) and inorganic polyphosphate), has been discovered in Gram-negative and Gram-positive bacteria. Both polymers are ubiquitous components of prokaryotic and eukaryotic cells, and each has unique physical-chemical properties relevant to ion conduction. The two polymers associate to form channels in lipid bilayers in vitro that exhibit voltage-activated conductance, are selective for divalent over monovalent cations, are permeant to Ca, Sr, and Ba, and are blocked by transition metal cations. These studies will define the structural determinants and basic molecular mechanisms that give rise to these properties. The polymer components, either isolated from bacteria or prepared synthetically, will be incorporated into lipid bilayers, and single-channel currents will be examined by voltage-clamp techniques under different defined conditions. Studies are designed to determine how factors that influence bilayer fluidity affect conductance, permeance, selectivity, and voltage-gating. Additional studies will determine the influence of pH on cation selectivity, the way Mg and other cations block Ca conductance, and the possible effects of agents known to be agonists and antagonists of protein calcium channels. These studies of a simple but apparently ubiquitous prokaryotic channel should provide insights into the general mechanisms of ion transfer across bilayers. The channels may be a model for a 'minimalist' calcium channel that was the progenitor during evolution of the protein calcium channels of eukaryotes.