Karlsruhe Institute of Technology (KIT), Institute of Biological Interfaces (IBG-2) , P.O. Box 3640, 76021 Karlsruhe , Germany.
Secció de Química Orgànica, Departament de Química Inorgànica i Orgànica, Facultat de Química , Universitat de Barcelona , 08028 Barcelona , Spain.
J Phys Chem B. 2018 Jun 14;122(23):6236-6250. doi: 10.1021/acs.jpcb.8b02661. Epub 2018 Jun 1.
The amphipathic α-helical peptide KIA14 [(KIAGKIA)-NH] was studied in membranes using circular dichroism and solid-state NMR spectroscopy to obtain global as well as local structural information. By analyzing H NMR data from 10 analogues of KIA14 that were selectively labeled with Ala- d, those positions that are properly folded into a helix could be determined within the membrane-bound peptide. The N-terminus was found to be unraveled, whereas positions 4-14 formed an ideal helix all the way to the C-terminus. The helicity did not change when Gly residues were replaced by Ala- d but was reduced when Ile was replaced, indicating that large hydrophobic residues are required for membrane binding and helix formation. The reduced helicity was strongly correlated with a decrease in peptide-induced leakage from lipid vesicles. The orientation of the short KIA14 peptide was assessed in several lipid systems and compared with that of the longer KIA21 sequence [(KIAGKIA)-NH]. In 1,2-dioleoyl- sn-glycero-3-phosphatidylcholine, both peptides are aligned flat on the membrane surface, whereas in 1,2-dimyristoyl- sn-glycero-3-phosphatidylcholine (DMPC)/1-myristoyl-2-hydroxy- sn-glycero-3-phosphatidylcholine (lyso-MPC) both are inserted into the membrane in an upright orientation. These two types of lipid systems had been selected for their strongly negative and positive spontaneous curvature, respectively. We propose that in these cases, the peptide orientation is largely determined by the lipid properties. On the other hand, in plain DMPC and 1,2-dilauroyl- sn-glycero-3-phosphatidylcholine, which have only a slight positive curvature, a marked difference in orientation is evident: the short KIA14 lies almost flat on the membrane surface, whereas the longer KIA21 is more tilted. We thus propose that out of the lipid systems tested here, DMPC (with hardly any curvature) is the least biased lipid system in which peptide orientation and realignment can be studied, allowing to compare and discriminate the intrinsic effects of the properties of the peptides as such.
采用圆二色性和固态 NMR 光谱学研究了两亲性α-螺旋肽 KIA14 [(KIAGKIA)-NH]在膜中的结构，以获得全局和局部结构信息。通过分析 10 种 KIA14 类似物的 1 H NMR 数据，这些类似物选择性地用 Ala-d 标记，可以确定膜结合肽中正确折叠成螺旋的位置。发现 N 端未解开，而位置 4-14 一直形成理想的螺旋到 C 端。当用 Ala-d 取代 Gly 残基时，螺旋性没有改变，但当用 Ile 取代时，螺旋性降低，表明大的疏水性残基对于膜结合和螺旋形成是必需的。肽诱导的脂质体渗漏减少与螺旋性降低强烈相关。在几种脂质系统中评估了短肽 KIA14 的取向，并与较长的 KIA21 序列 [(KIAGKIA)-NH]进行了比较。在 1,2-二油酰基-sn-甘油-3-磷酸胆碱中，两种肽都在膜表面上排列整齐，而在 1,2-二肉豆蔻酰基-sn-甘油-3-磷酸胆碱 (DMPC)/1-肉豆蔻酰基-2-羟基-sn-甘油-3-磷酸胆碱 (lyso-MPC) 中，两种肽都以垂直的方式插入膜中。这两种类型的脂质系统因其具有很强的负和正自发曲率而被选择。我们提出，在这些情况下，肽的取向主要由脂质特性决定。另一方面，在具有轻微正曲率的普通 DMPC 和 1,2-二棕榈酰基-sn-甘油-3-磷酸胆碱中，短肽 KIA14 几乎完全平卧在膜表面上，而较长的 KIA21 则更倾斜。因此，我们提出，在所测试的脂质系统中，DMPC（几乎没有曲率）是最不偏向的脂质系统，可以在其中研究肽的取向和重排，从而可以比较和区分肽本身性质的内在影响。
