Fukushima K, Sakamoto T, Tsuji J, Kondo K, Shimozawa R
Department of Chemistry, Faculty of Science, Fukuoka University, Japan.
Biochim Biophys Acta. 1994 Apr 20;1191(1):133-40. doi: 10.1016/0005-2736(94)90240-2.
Static and dynamic circular dichroism (CD) measurements were carried out for poly(L-lysine) in suspensions of dilauroylphosphatidic acid (DLPA) vesicles at alkaline pH (8-11.5). The static experiments demonstrated that the alpha-helix of poly(L-lysine) induced by deprotonation in alkaline solutions is transformed to beta-structure by the addition of DLPA vesicles. Stopped-flow CD measurements for such order-to-order transition revealed that the rate determining step is the unfolding process of alpha-helix to random coil. Previously, we have reported the conformational change of poly(L-lysine) induced by DLPA vesicles at neutral pH, where the beta-structure transition from random coil was observed. Thus two types of transition of poly(L-lysine) are observed depending on bulk pH, i.e., from random coil to beta-structure and from alpha-helix to beta-structure. So far the phospholipid-induced conformations of poly(L-lysine) were interpreted in terms of counterbalance between the positively charged terminals of the lysyl chains and the negative headgroups of the phospholipid in vesicle. However, present work indicates the direct interaction other than electrostatic interaction between the lysyl chain and phosphate groups of the lipid.
在碱性pH值（8 - 11.5）下，对二月桂酰磷脂酸（DLPA）囊泡悬浮液中的聚（L - 赖氨酸）进行了静态和动态圆二色性（CD）测量。静态实验表明，碱性溶液中通过去质子化诱导形成的聚（L - 赖氨酸）α - 螺旋，在添加DLPA囊泡后转变为β - 结构。对这种从一种有序结构到另一种有序结构转变的停流CD测量显示，速率决定步骤是α - 螺旋向无规卷曲的展开过程。此前，我们报道了在中性pH值下DLPA囊泡诱导的聚（L - 赖氨酸）构象变化，其中观察到了从无规卷曲向β - 结构的转变。因此，根据整体pH值观察到聚（L - 赖氨酸）有两种类型的转变，即从无规卷曲到β - 结构以及从α - 螺旋到β - 结构。到目前为止，磷脂诱导的聚（L - 赖氨酸）构象是根据赖氨酸链的带正电末端与囊泡中磷脂的负头基之间的平衡来解释的。然而，目前的工作表明赖氨酸链与脂质的磷酸基团之间除了静电相互作用之外还存在直接相互作用。
