The Dynamics of Circulatory Zinc Handling and Transport

哺乳动物的生命需要25种化学元素，其中15种是金属。锌，以Zn2+的电离形式，是哺乳动物必不可少的金属离子，通过允许许多重要的化学反应发生，发挥着广泛的重要生理功能。众所周知，锌在生育和发育、免疫系统、衰老以及阿尔茨海默氏症、糖尿病和癌症等重大疾病中发挥着重要作用。然而，不幸的是，锌从饮食中被隔离后进入血液并到达需要它的地方的分子机制尚不完全清楚。众所周知，一种叫做血清白蛋白的特殊蛋白质（在血液中含量很高）在血液中运输锌（以及其他金属，包括钙和镁）方面起着重要作用。血清白蛋白不仅携带锌通过循环系统，而且介导其进入细胞的摄取。控制锌与血清白蛋白相互作用及其进入细胞的分子机制在很大程度上是未知的。了解这些相互作用很重要。白蛋白也运输其他类型的分子（如脂肪酸、激素），一个特定分子的结合可以影响另一个单独位点的结合。例如，我们之前发现了一个锌位点，它被分子上其他地方的脂肪酸结合所干扰。因此，改变血液小分子组成的生理事件可以改变金属的运输过程。这些事件可能是短期的（如禁食、进食、感染、中风），也可能是长期的（肥胖、疾病）。由于金属结合/传递改变所引起的连锁反应，血液化学的长期改变尤其可能产生严重后果。我们已经在分子上确定了三个可能形成新的金属结合位点的区域。我们将通过在每个位点合成突变的血清白蛋白来研究这些区域是否参与或影响锌的运输。这些改变会去除可能参与金属结合的重要化学基团。每个“改变的蛋白质”结合锌和其他相关金属的能力将被检查，并使用互补方法与天然（或“正常”）蛋白质进行比较。我们还将研究分子（包括金属）在其他位点的结合是否会改变每个位点的结合特性。已知和新发现的锌结合位点在介导锌摄取进入培养血管内皮细胞（一种排列在血管上的特殊类型的细胞）中的重要性将通过将这些细胞与含有每个锌位点和锌生理水平改变的白蛋白孵育来确定。然后将测量细胞吸收锌的量。这些实验的结果将使我们更好地了解金属离子在循环系统中的运输方式。特别是关于可以改变这一过程的事件和白蛋白在介导细胞锌摄取中的重要性。这提供了重要的生理信息，将有助于我们了解各种涉及金属的生理和疾病过程，并有助于他们的研究。

There are 25 chemical elements that are required for mammalian life, 15 of these elements are metals. Zinc, in its ionised form Zn2+, is an essential metal ion in mammals and performs a wide range of important physiological functions by allowing many vital chemical reactions to occur. Zinc is known to play roles in fertility and development, the immune system, ageing, and major diseases such as Alzheimer's, diabetes, and cancer. Unfortunately however, the molecular mechanisms that enable zinc to get to where it is needed after it enters the bloodstream, following sequestration from the diet, are not fully understood.It is known that a particular protein called serum albumin (that is highly abundant in the blood) plays an important role in transporting zinc (and other metals including calcium and magnesium) in the blood. Serum albumin not only carries zinc through the circulatory system but also mediates its uptake into cells. The molecular mechanisms that control the interaction between zinc and serum albumin and its uptake into cells are largely unknown. It is important that these interactions are understood. Albumin also transports other types of molecules (e.g. fatty acids, hormones) and binding of one particular molecule can affect binding of another at a separate site. For example, we previously identified a zinc site that is perturbed by fatty acid-binding elsewhere on the molecule. Physiological events that alter the small molecule composition of blood can therefore alter metal transport processes. Such events may be short-term (e.g. fasting, eating, infection, stroke) or long-term (obesity, disease). Long-term alterations in blood chemistry are particularly likely to have serious consequences due to the knock-on effects caused by altered metal binding/delivery.We have identified three regions on the molecule that are likely to form novel metal binding sites. We will examine whether these regions that are involved in or impact upon zinc transport by synthesising mutant serum albumin proteins with chemical alterations at each site. These alterations will remove important chemical groups that are likely to participate in metal binding. The ability of each "altered protein" to bind zinc and other relevant metals will be examined and compared to the native (or "normal") protein using complementary approaches. We will also examine whether binding of molecules (including metals) at other sites alters the binding properties of each site.The importance of known and newly identified zinc-binding sites in mediating zinc uptake into cultured vascular endothelial cells (a particular type of cell that lines the blood vessels) will be determined by incubating these cells with albumins that contain alterations at each zinc site and physiological levels of zinc. The amount of zinc taken up by the cells will then be measured. The outcome of these experiments will allow a better understanding of how metal ions are transported in the circulatory system. Particularly with regard to the events that can alter this process and the importance of albumin in mediating cellular zinc uptake. This provides important physiological information that will help us to understand a variety of physiological and disease processes that involve metals and will aid in their study.