Luo Wenbin, Cady Sarah D, Hong Mei
Department of Chemistry, Iowa State University, Ames, Iowa 50011, USA.
Biochemistry. 2009 Jul 14;48(27):6361-8. doi: 10.1021/bi900716s.
The dynamic and structural properties of membrane proteins are intimately affected by the lipid bilayer. One property of membrane proteins is uniaxial rotational diffusion, which depends on the membrane viscosity and thickness. This rotational diffusion is readily manifested in solid-state NMR spectra as characteristic line shapes and temperature-dependent line narrowing or broadening. We show here that this whole-body uniaxial diffusion is suppressed in lipid bilayers mimicking the composition of eukaryotic cell membranes, which are rich in cholesterol and sphingomyelin. We demonstrate this membrane-induced immobilization on the transmembrane peptide of the influenza A M2 (AM2-TM) proton channel protein. At physiological temperature, AM2-TM undergoes uniaxial diffusion faster than approximately 10(5) s(-1) in DLPC, DMPC, and POPC bilayers, but the motion is slowed by 2 orders of magnitude, to <10(3) s(-1), in a cholesterol-rich virus envelope-mimetic membrane ("viral membrane"). The immobilization is manifested as near rigid-limit (2)H quadrupolar couplings and (13)C-(1)H, (15)N-(1)H, and (13)C-(15)N dipolar couplings for all labeled residues. The immobilization suppresses intermediate time scale broadening of the NMR spectra, thus allowing high-sensitivity and high-resolution spectra to be measured at physiological temperature. The conformation of the protein in the viral membrane is more homogeneous than in model PC membranes, as evidenced by the narrow (15)N lines. The immobilization of the M2 helical bundle by the membrane composition change indicates the importance of studying membrane proteins in environments as native as possible. It also suggests that eukaryote-mimetic lipid membranes may greatly facilitate structure determination of membrane proteins by solid-state NMR.
膜蛋白的动力学和结构特性受到脂质双层的密切影响。膜蛋白的一个特性是单轴旋转扩散,它取决于膜的粘度和厚度。这种旋转扩散在固态核磁共振谱中很容易表现为特征性的线形以及温度依赖性的谱线变窄或变宽。我们在此表明,在模拟富含胆固醇和鞘磷脂的真核细胞膜组成的脂质双层中,这种整体单轴扩散受到抑制。我们在甲型流感病毒M2(AM2-TM)质子通道蛋白的跨膜肽段上证实了这种膜诱导的固定化。在生理温度下,AM2-TM在二油酰磷脂酰胆碱(DLPC)、二肉豆蔻酰磷脂酰胆碱(DMPC)和1-棕榈酰-2-油酰磷脂酰胆碱(POPC)双层中进行单轴扩散的速度快于约10⁵ s⁻¹,但在富含胆固醇的模拟病毒包膜膜(“病毒膜”)中,运动速度减慢了2个数量级,降至<10³ s⁻¹。这种固定化表现为所有标记残基的近乎刚性极限的²H四极耦合以及¹³C-¹H、¹⁵N-¹H和¹³C-¹⁵N偶极耦合。这种固定化抑制了核磁共振谱的中间时间尺度展宽,从而使得能够在生理温度下测量高灵敏度和高分辨率的谱图。如¹⁵N谱线变窄所示,病毒膜中蛋白质的构象比在模型磷脂酰胆碱膜中更均匀。膜组成变化导致M2螺旋束的固定化表明,在尽可能天然的环境中研究膜蛋白非常重要。这也表明,模拟真核生物的脂质膜可能极大地促进通过固态核磁共振确定膜蛋白的结构。