Koppenhagen F J, Visser A J, Herron J N, Storm G, Crommelin D J
Department of Pharmaceutics, Utrecht Institute for Pharmaceutical Sciences, Utrecht University, 3508 TB Utrecht, The Netherlands.
J Pharm Sci. 1998 Jun;87(6):707-14. doi: 10.1021/js9704386.
Liposomes have been employed as a delivery system for recombinant interleukin-2 (rIL-2) in cancer immunotherapy. In this study the effects of the rIL-2-bilayer interaction on protein structure were investigated. It was shown that rIL-2 adsorbs to liposomal membranes when added to preformed liposomes. Polarized fluorescence decay studies showed that the single tryptophan in "native" rIL-2 has a relatively large motional freedom, although iodide quenching of this residue's fluorescence was relatively ineffective. However, adsorption of rIL-2 to liposomes alters this situation dramatically- fluorescence intensity increased 2-fold and the residue became more susceptible to iodide quenching. At the same time, the average fluorescence lifetime of the fluorophore is extended. Interestingly, circular dichroism studies showed that no major conformational changes occurred in rIL-2's secondary structure upon adsorption. These observations support the hypothesis that intramolecular quenching takes place in the native rIL-2 molecule, which is abrogated upon adsorption to the liposomal membrane, resulting in a higher fluorescence intensity. Fluorescence anisotropy decay experiments indicate that the protein forms self-aggregates under the low-ionic strength conditions used, confirming the earlier observations on the tendency of the protein to precipitate in salt-containing media.
脂质体已被用作癌症免疫治疗中重组白细胞介素 -2（rIL -2）的递送系统。在本研究中，研究了rIL -2与双层膜的相互作用对蛋白质结构的影响。结果表明，当将rIL -2添加到预先形成的脂质体中时，它会吸附到脂质体膜上。偏振荧光衰减研究表明，“天然”rIL -2中的单个色氨酸具有相对较大的运动自由度，尽管该残基荧光的碘化物猝灭相对无效。然而，rIL -2吸附到脂质体上会极大地改变这种情况——荧光强度增加了2倍，并且该残基变得更容易受到碘化物猝灭的影响。同时，荧光团的平均荧光寿命延长。有趣的是，圆二色性研究表明，rIL -2吸附后其二级结构没有发生重大构象变化。这些观察结果支持了这样的假设，即天然rIL -2分子中发生分子内猝灭，而吸附到脂质体膜上后这种猝灭被消除，导致荧光强度更高。荧光各向异性衰减实验表明，在所用的低离子强度条件下蛋白质形成了自聚集体，这证实了早期关于该蛋白质在含盐介质中沉淀倾向的观察结果。
