Monsalve R I, Villalba M, López-Otín C, Rodríguez R
Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad Complutense, Madrid, Spain.
Biochim Biophys Acta. 1991 Jun 24;1078(2):265-72. doi: 10.1016/0167-4838(91)90568-k.
Napin nIII is a 2S albumin from rapeseed (Brassica napus L.) homologous to the major mustard allergen. It is composed of two different polypeptide chains linked by two disulphide bonds. The small chain has been isolated by reverse-phase HPLC after reduction of the native protein and its primary structure elucidated. This 37 residue polypeptide contains only two cysteines, at positions 10 and 23, which show a great tendency to form a non-native intramolecular disulphide bridge. The kinetic analysis of this process was performed by measuring the fluorescence emission of the single tryptophan residue of the molecule since its fluorescence intensity is about 30% decreased during disulphide formation. Small changes on the secondary structure of the polypeptide were measured by circular dichroism. The process is delayed in the presence of the reduced large chain of nIII. However, no dimer formation was detected under the conditions used, either between small chains or between the small and the large chains. Thus, the interchain disulphide formation in napin nIII should be considered as an early step during maturation of this multi-subunit seed protein.
napin nIII是一种来自油菜籽（甘蓝型油菜）的2S白蛋白，与主要的芥菜过敏原同源。它由两条不同的多肽链通过两个二硫键连接而成。在还原天然蛋白质后，通过反相高效液相色谱法分离出小链，并阐明了其一级结构。这条37个残基的多肽仅在第10位和第23位含有两个半胱氨酸，它们极易形成非天然的分子内二硫键。由于在二硫键形成过程中分子中单个色氨酸残基的荧光强度降低约30%，因此通过测量该分子的荧光发射对这一过程进行了动力学分析。通过圆二色性测量多肽二级结构的微小变化。在存在还原型nIII大链的情况下，该过程会延迟。然而，在所使用的条件下，未检测到小链之间或小链与大链之间形成二聚体。因此，napin nIII中的链间二硫键形成应被视为这种多亚基种子蛋白成熟过程中的早期步骤。
