Singh B R, Evenson M L, Bergdoll M S
Food Research Institute, University of Wisconsin--Madison 53706.
Biochemistry. 1988 Nov 29;27(24):8735-41. doi: 10.1021/bi00424a008.
Secondary and tertiary structural parameters of two functionally and serologically related proteins, staphylococcal enterotoxins B and C1, have been determined by using circular dichroism and fluorescence spectroscopy. The secondary structures derived from the respective far-UV circular dichroic spectra were 9.5% alpha-helix, 55.0% beta-pleated sheets, 16.5% beta-turns, and 19.0% random coils for enterotoxin B and 15.0% alpha-helix, 38.0% beta-pleated sheets, 25.5% beta-turns, and 21.5% random coils for staphylococcal enterotoxin C1. The values matched well with the secondary structures derived from the amino acid sequences (Chou and Fasman method). Seven antigenic sites have been predicted for both staphylococcal enterotoxins B and C1 by using the hydrophilicity and the secondary structure information. Three of these antigenic sites appear similar. Fluorescence quantum yield of the single tryptophan residue (Trp-197) of both the enterotoxins showed the tryptophan residue in staphylococcal enterotoxin B to be approximately 46% more fluorescent than in staphylococcal enterotoxin C1. Tryptophan fluorescence quenching by the surface quencher I- and the neutral quencher acrylamide revealed that the single tryptophan residue in each of the enterotoxins is buried in the protein matrix and is not accessible to the surface quencher I-. The tryptophan residue in staphylococcal enterotoxin C1 is 14% less accessible to acrylamide than in staphylococcal enterotoxin B. The data, in general, reflect several similarities and significant differences between the two related enterotoxins.
利用圆二色光谱法和荧光光谱法测定了两种在功能和血清学上相关的蛋白质——葡萄球菌肠毒素B和C1的二级和三级结构参数。从各自的远紫外圆二色光谱得出的二级结构为：肠毒素B的α螺旋占9.5%、β折叠片占55.0%、β转角占16.5%、无规卷曲占19.0%；葡萄球菌肠毒素C1的α螺旋占15.0%、β折叠片占38.0%、β转角占25.5%、无规卷曲占21.5%。这些数值与根据氨基酸序列推导的二级结构（Chou和Fasman方法）非常吻合。利用亲水性和二级结构信息，预测了葡萄球菌肠毒素B和C1的七个抗原位点。其中三个抗原位点看起来相似。两种肠毒素中单个色氨酸残基（Trp-197）的荧光量子产率表明，葡萄球菌肠毒素B中的色氨酸残基荧光比葡萄球菌肠毒素C1中的约高46%。表面淬灭剂I⁻和中性淬灭剂丙烯酰胺对色氨酸荧光的淬灭表明，每种肠毒素中的单个色氨酸残基都埋藏在蛋白质基质中，表面淬灭剂I⁻无法接近。与葡萄球菌肠毒素B相比，丙烯酰胺对葡萄球菌肠毒素C1中色氨酸残基的可及性低14%。总体而言，这些数据反映了这两种相关肠毒素之间的一些相似性和显著差异。
