Dockal M, Carter D C, Rüker F
Institute of Applied Microbiology, University of Agricultural Sciences, Muthgasse 18, A-1190 Vienna, Austria.
J Biol Chem. 2000 Feb 4;275(5):3042-50. doi: 10.1074/jbc.275.5.3042.
Human serum albumin (HSA) is a protein of 66.5 kDa that is composed of three homologous domains, each of which displays specific structural and functional characteristics. HSA is known to undergo different pH-dependent structural transitions, the N-F and F-E transitions in the acid pH region and the N-B transition at slightly alkaline pH. In order to elucidate the structural behavior of the recombinant HSA domains as stand-alone proteins and to investigate the molecular and structural origins of the pH-induced conformational changes of the intact molecule, we have employed fluorescence and circular dichroic methods. Here we provide evidence that the loosening of the HSA structure in the N-F transition takes place primarily in HSA-DOM III and that HSA-DOM I undergoes a structural rearrangement with only minor changes in secondary structure, whereas HSA-DOM II transforms to a molten globule-like state as the pH is reduced. In the pH region of the N-B transition of HSA, HSA-DOM I and HSA-DOM II experience a tertiary structural isomerization, whereas with HSA-DOM III no alterations in tertiary structure are observed, as judged from near-UV CD and fluorescence measurements.
人血清白蛋白（HSA）是一种66.5 kDa的蛋白质，由三个同源结构域组成，每个结构域都具有特定的结构和功能特征。已知HSA会经历不同的pH依赖性结构转变，在酸性pH区域有N-F和F-E转变，在略碱性pH时有N-B转变。为了阐明重组HSA结构域作为独立蛋白质的结构行为，并研究完整分子pH诱导构象变化的分子和结构起源，我们采用了荧光和圆二色性方法。在此我们提供证据表明，HSA在N-F转变中结构的松弛主要发生在HSA-DOM III中，HSA-DOM I经历了结构重排，二级结构仅有微小变化，而随着pH降低，HSA-DOM II转变为类似熔球的状态。在HSA的N-B转变的pH区域，根据近紫外圆二色性和荧光测量判断，HSA-DOM I和HSA-DOM II经历了三级结构异构化，而HSA-DOM III的三级结构未观察到变化。
