Electron Transfer in Extremely Halophilic Bacteria

以高离子强度形式存在的环境压力已被许多生物体以多种方式克服。一般来说，人们对极端嗜盐菌中的电子转移或耦合能量守恒知之甚少。在初步研究中，研究人员发现，从非嗜盐细菌中观察到的蛋白质的电子转移机制必须与极端嗜盐细菌的电子转移机制不同，因为静电似乎在电子转移过程中起着重要作用。因此，在中度和极端嗜盐菌中，在周质空间中工作的蛋白质必须通过使用除静电学以外的其他因素来控制特异性。此外，极端和中度嗜盐菌似乎具有氧化还原蛋白质，其氧化还原电位一般较低，是强酸性的，并且在至少两种情况下具有氧化还原电位，该电位在高离子强度时依赖于离子强度。因此，似乎在适应高离子强度环境的过程中，在分子水平上发生了结构变化。应该强调的是，耐盐细菌，即那些在有盐和没有盐的情况下都能生存的细菌，与淡水细菌没有明显的区别。这笔拨款将用于研究三种嗜盐生物。这些细菌中的可溶性氧化还原蛋白(C型细胞色素和铁硫蛋白)将根据位置以及渗透压调节剂和离子强度对氧化还原电位、光谱性质和热变性的影响进行表征。数据将根据已知的结构特性进行分析，并利用相关蛋白质的三维结构进行计算机建模。最后，我们将研究一些基本的生理过程。预计拟议的研究将为控制生物电子转移的分子性质提供新的见解，更好地了解嗜盐微生物的生理学，并增加我们对控制蛋白质稳定性的结构和化学参数的了解。

Environmental stress in the form of high ionic strength has been surmounted by a number of organisms in a number of ways. In general, little is known about electron transfer or coupled energy conservation in any of the extreme halophiles. In preliminary studies, the investigator has found that electron transfer mechanisms observed with proteins from nonhalophilic bacteria must be distinct from the extreme halophiles, as electrostatics appear to play an important role in the elctron transfer proecss. Thus, proteins operating in the periplasmic space in moderate and extreme halophiles must control specificity by the use of factors other than electrostatics. In addition, extreme and moderate halophiles appear to have redox proteins which have generally lower redox potentials, are strongly acidic, and in at least two cases have redox potentials which are ionic strength-dependent at high ionic strengths. Thus it appears that in the course of adaptation to a high ionic strength environment, structural alterations at the molecular level have taken place. It should be emphasized that halotolerant bacteria, those able to live both with and without salt, are not obviously different from fresh-water bacteria. Three halophilic organisms will be studied with this grant. Soluble redox proteins (c-type cytochromes and iron-sulfur proteins) from these bacteria will be characterized in terms of location and the effect of osmoregulators and ionic strength on redox potentials, spectral properties, and thermal denaturation. Data will be analyzed in terms of known structural properties and supplemented by computer modeling utilizing 3-D structures of related proteins. Finally, some basic physiological processes will be studied. It is anticipated that the proposed studies will provide new insights into the molecular properties controlling biological electron transfer, a better understanding of the physiology of halophiles, and an increase in our knowledge of the structural and chemical parameters that control protein stability.