Nishizawa Manami, Nishizawa Kazuhisa
Department of Biochemistry, Teikyo University School of Medicine, Kaga, Itabashi, Tokyo 173-8605, Japan.
Biophys J. 2007 Jun 15;92(12):4233-43. doi: 10.1529/biophysj.106.101071. Epub 2007 Mar 23.
Our recent molecular dynamics simulation study of hanatoxin 1 (HaTx1), a gating modifier that binds to the voltage sensor of K(+) channels, has shown that HaTx1 has the ability to interact with carbonyl oxygen atoms of both leaflets of the lipid bilayer membrane and to be located at a deep position within the membrane. Here we performed a similar study of GsMTx4, a stretch-activated channels inhibitor, belonging to the same peptide family as HaTx1. Both toxins have an ellipsoidal shape, a belt of positively charged residues around the periphery, and a hydrophobic protrusion. Results show that, like HaTx1, GsMTx4 can interact with the membrane in two different ways. When all the positively charged residues interact with the outer leaflet lipid, GsMTx4 can assume a shallow binding mode. On the other hand, when the electrostatic interaction brings the positively charged groups of K-8 and K-28 into the vicinity of the carbonyl oxygen atoms of the inner leaflet lipids, the system exhibits a deep binding mode. This deep mode is accompanied by local membrane thinning. For both HaTx1 and GsMTx4, our mean force measurement analyses show that the deep binding mode is energetically favored over the shallow mode when a DPPC (dipalmitoyl-phosphatidylcholine) membrane is used at 310 K. In contrast, when a POPC (palmitooleoyl-phosphatidylcholine) membrane is used at 310 K, the two binding modes exhibited similar stability for both toxins. Similar analyses with DPPC membrane at 330 K led to an intermediary result between the above two results. Therefore, the structure of the lipid acyl chains appears to influence the location and the dynamics of the toxins within biological membranes. We also compared the behavior of an arginine and a lysine residue within the membrane. This is of interest because the arginine residue interaction with the lipid carbonyl oxygen atoms mediates the deep binding mode for HaTx1, whereas the lysine residue plays that role for GsMTx4. The arginine residue generally shows smoother dynamics near the lipid carbonyl oxygen atoms than the lysine residue. This difference between arginine and lysine may partly account for the functional diversity of the members of the toxin family.
我们最近对汉纳毒素1（HaTx1）进行的分子动力学模拟研究表明，HaTx1是一种与钾离子通道电压感受器结合的门控修饰剂，它能够与脂质双分子层膜两侧的羰基氧原子相互作用，并位于膜内较深的位置。HaTx1属于与伸展激活通道抑制剂GsMTx4相同的肽家族。在这里，我们对GsMTx4进行了类似的研究。两种毒素均呈椭圆形，外周有一条带正电荷的残基带，还有一个疏水突起。结果表明，与HaTx1一样，GsMTx4可以通过两种不同方式与膜相互作用。当所有带正电荷的残基与外层小叶脂质相互作用时，GsMTx4可呈现浅结合模式。另一方面，当静电相互作用使K-8和K-28的带正电荷基团靠近内层小叶脂质的羰基氧原子时，系统呈现深结合模式。这种深模式伴随着局部膜变薄。对于HaTx1和GsMTx4，我们的平均力测量分析表明，在310K使用二棕榈酰磷脂酰胆碱（DPPC）膜时，深结合模式在能量上比浅模式更有利。相反，在310K使用棕榈油酰磷脂酰胆碱（POPC）膜时，两种结合模式对两种毒素均表现出相似的稳定性。在330K对DPPC膜进行类似分析得到了介于上述两种结果之间的中间结果。因此，脂质酰基链的结构似乎会影响毒素在生物膜中的位置和动态。我们还比较了膜内精氨酸和赖氨酸残基的行为。这一点很重要，因为精氨酸残基与脂质羰基氧原子的相互作用介导了HaTx1的深结合模式，而赖氨酸残基则对GsMTx4起这一作用。精氨酸残基在脂质羰基氧原子附近通常比赖氨酸残基表现出更平滑的动态。精氨酸和赖氨酸之间的这种差异可能部分解释了毒素家族成员的功能多样性。
