Surewicz W K, Surewicz K, Mantsch H H, Auclair F
Division of Chemistry, National Research Council of Canada, Ottawa, Ontario.
Biochem Biophys Res Commun. 1989 Apr 14;160(1):126-32. doi: 10.1016/0006-291x(89)91630-6.
The interaction of the B-subunit of Shigella toxin with a globotriaosyl ceramide receptor incorporated into phosphatidylcholine vesicles was studied by fluorescence spectroscopy. From the position of the maximum in the emission spectrum and the accessibility to acrylamide quenching, it is concluded that a single tryptophan of a free B-chain is located in a highly polar environment, most likely on the surface of the folded polypeptide chain. Binding of B-subunits to the membrane-associated globotriaosyl ceramide results in a strong enhancement of fluorescence intensity and a small blue-shift of the emission maximum; these effects suggest a conformational change in the protein which provides a new environment to a tryptophan residue. However, the polarity of this new environment is still relatively high--as indicated by the position of the emission maximum at 344 nm--and suggests that the receptor-bound B-chain remains largely on the membrane surface, without penetrating the hydrophobic interior of a lipid bilayer. On the other hand, the A-chains are shown to interact directly with the receptor-free lipid bilayers; this nonspecific interaction may play a role in the mechanism by which A-subunit traverses the membrane of a target cell.
通过荧光光谱法研究了志贺氏菌毒素B亚基与掺入磷脂酰胆碱囊泡中的球三糖基神经酰胺受体之间的相互作用。从发射光谱中最大值的位置以及丙烯酰胺淬灭的可及性可以得出结论，游离B链的单个色氨酸位于高度极性的环境中，很可能在折叠多肽链的表面。B亚基与膜相关的球三糖基神经酰胺结合会导致荧光强度强烈增强以及发射最大值出现小的蓝移；这些效应表明蛋白质发生了构象变化，为色氨酸残基提供了新的环境。然而，这个新环境的极性仍然相对较高——发射最大值在344nm处的位置表明了这一点——这表明与受体结合的B链主要仍留在膜表面，而没有穿透脂质双层的疏水内部。另一方面，已表明A链直接与无受体的脂质双层相互作用；这种非特异性相互作用可能在A亚基穿过靶细胞膜的机制中起作用。
