Membrane Biophysics Via Atomic Force Microscopy

脂质膜的物理化学性质和异质性对许多生物过程都很重要，本项目正在与NIAID合作者利用原子力显微镜（AFM）进行研究。在环境控制的不同温度条件下，利用点射式原子力显微镜分析了2-二myristoyl- son -glycero-phosphocholine （DMPC）的主相转变。这些AFM图像显示两个膜相接近预期的DMPC链熔化温度。通过精确的AFM厚度测量，我们量化了链熔化时DMPC膜的显着变薄和机械软化。我们还构建了一个新的生物物理模型，该模型可以根据afm获得的温度相关相分布来估计热力学转变焓、熵和膜相域大小。推导出的本征畴直径约为4.2 nm。对DMPC膜的研究已经扩展到在(1)双棕榈酰磷脂酰胆碱（DPPC）、二脲酰磷脂酰胆碱（DLPC）和胆固醇（Chol）的三脂混合物和(2)红细胞膜中检测更多的生物膜微结构域或筏。我们发现三脂膜在云母基质上形成微观和纳米级结构域；胆固醇水平和温度都会影响这些结构域的大小和动态。我们开发了新的视频显微镜和图像分析来表征恶性疟原虫疟疾感染过程中的红细胞闪烁和边缘抖动现象。我们发现寄生虫感染显著改变了细胞膜动力学，这可能与微循环中的疟疾疾病机制有关。总的来说，AFM和相关技术正在进一步发展，以阐明对医学重要过程至关重要的膜相关生物分子事件。

The physical-chemical properties and heterogeneities of lipid membranes, which are important to many biological processes, are being investigated by atomic force microscopy (AFM) in this project with NIAID collaborators. Quantitative features of the main phase transition in 2-dimyristoyl-sn-glycero-phosphocholine (DMPC) have been resolved by tapping-mode AFM images in an environmentally controlled chamber at various temperatures. These AFM images reveal two membrane phases near the expected DMPC chain-melting temperature. We have quantified the marked thinning and mechanical softening of the DMPC membrane upon chain melting from precise AFM thickness measurements. We have also constructed a novel biophysical model, which permits an estimate of the thermodynamic transition enthalpy, entropy, and the membrane phase domain size from our AFM-acquired temperature-dependent phase distributions. The deduced intrinsic domain size is about 4.2 nm in diameter. The work on DMPC membrane has been extended to examine the more biological membrane microdomains, or rafts, in (1) tri-lipid mixtures of dipalmitoyl phosphatidylcholine (DPPC), dilauroyl phosphatidylcholine (DLPC), and cholesterol (Chol), and (2) red blood cell membranes. We found that the tri-lipid membrane formed both microscopic and nanoscopic domains over mica substrates; both the cholesterol level and the temperature affected the sizes and dynamic of these domains. We developed new video microscopy and image analyses to characterize the red blood cell flicker and edge dithering phenomena during the Plasmodium falciparum malaria infection process. We found that the parasitic infection markedly modifies cell membrane dynamics, in potential relevance to malaria disease mechanism in microcirculations. Overall, the AFM and related technology are being advanced further to elucidate membrane-associated biomolecular events critical to medically important processes.