Pegoraro S, Fiori S, Cramer J, Rudolph-Böhner S, Moroder L
Max-Planck-Institut für Biochemie, Martinsried, Germany.
Protein Sci. 1999 Aug;8(8):1605-13. doi: 10.1110/ps.8.8.1605.
The sequence of apamin, an 18 residue bee venom toxin, encloses all the information required for the correct disulfide-coupled folding into the cystine-stabilized alpha-helical motif. Three apamin analogs, each containing a pair of selenocysteine residues replacing the related cysteines, were synthesized to mimic the three possible apamin isomers with two crossed, parallel, or consecutive disulfides, respectively. Refolding experiments clearly revealed that the redox potential of selenocysteine prevails over the sequence encoded structural information for proper folding of apamin. Thus, selenocysteine can be used as a new device to generate productive and nonproductive folding intermediates of peptides and proteins. In fact, disulfides are selectively reduced in presence of the diselenide and the conformational features derived from these intermediates as well as from the three-dimensional (3D) structures of the selenocysteine-containing analogs with their nonnatural networks of diselenide/disulfide bridges allowed to gain further insight into the subtle driving forces for the correct folding of apamin that mainly derive from local conformational preferences.
蜂毒明肽是一种由18个残基组成的蜂毒毒素，其序列包含了正确形成二硫键偶联折叠成胱氨酸稳定的α-螺旋基序所需的所有信息。合成了三种蜂毒明肽类似物，每种类似物都含有一对硒代半胱氨酸残基取代相关的半胱氨酸，分别模拟三种可能的蜂毒明肽异构体，其具有两个交叉、平行或连续的二硫键。复性实验清楚地表明，硒代半胱氨酸的氧化还原电位在蜂毒明肽正确折叠的序列编码结构信息之上占主导地位。因此，硒代半胱氨酸可作为一种新工具来生成肽和蛋白质的有效和无效折叠中间体。事实上，在二硒键存在的情况下，二硫键会被选择性还原，并且这些中间体以及含硒代半胱氨酸类似物的三维（3D）结构所衍生的构象特征，其具有非天然的二硒键/二硫键网络，这使得我们能够进一步深入了解蜂毒明肽正确折叠的微妙驱动力，这些驱动力主要源于局部构象偏好。
