Poly (3-Hydroxybutyrate)/Polyphosphate Ion Channels

离子通道是膜中的大分子孔，其允许所选离子通过脂质双层转移。 这些通道大多由蛋白质或肽组成。 然而，在革兰氏阴性菌和革兰氏阳性菌中发现了由两种简单的线性均聚物（聚（3-羟基丁酸酯）和无机多磷酸盐）组成的非蛋白质钙选择性通道。 这两种聚合物是原核和真核细胞中普遍存在的组分，并且每种聚合物都具有与离子传导相关的独特物理化学性质。 这两种聚合物在体外形成脂质双层通道，表现出电压激活的电导，对二价阳离子的选择性超过一价阳离子，对Ca、Sr和Ba是渗透性的，并被过渡金属阳离子阻断。 这些研究将确定产生这些性质的结构决定因素和基本分子机制。 将从细菌中分离或合成制备的聚合物组分掺入脂质双层中，并在不同的限定条件下通过电压钳技术检查单通道电流。 研究旨在确定影响双层流动性的因素如何影响电导、渗透性、选择性和电压门控。 其他研究将确定pH值对阳离子选择性的影响，Mg和其他阳离子阻断Ca电导的方式，以及已知为蛋白质钙通道激动剂和拮抗剂的药物的可能影响。 这些研究一个简单的，但显然无处不在的原核通道，应提供深入了解跨双层离子转移的一般机制。 这些通道可能是“极简”钙通道的模型，该通道是真核生物蛋白质钙通道进化过程中的祖先。

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.