Imaging membrane proteins using atomic force microscopy techniques.

摘要

Thousands of different membrane proteins exist in the human body and reside in the membranes of cells. Structural information regarding these proteins can provide insight into the function of these proteins. Acquiring membrane protein structural information is difficult, especially when preparation techniques that are traditionally used for soluble proteins such as crystallizing and isolating proteins are not easily adapted for membrane proteins. The atomic force microscope (AFM) provides an alternative for imaging membrane proteins. The preparation required does not require crystallizing or isolating proteins, and can imagine membrane proteins in their native environment. Techniques are explored that can utilize the AFM for imaging proteins, including examining isolated cell membrane patches and membrane surfaces. One technique utilizes plasma membrane from Xenopus laevis oocytes as a model system to study membrane.; A novel technique is developed to isolate oocyte membranes by bursting the oocyte and depositing its membrane on a flat mica substrate. The flat surface membrane preparation allows high-resolution AFM images to be obtained, revealing a novel structure of densely packed particles. These particles exhibit a regular, repeating pattern of a lattice-like array with orderly packing, and are thus termed “lattice-like array particles” (LAPs). The LAPs are orderly yet imperfectly packed, are located in depressed pools, occur with a low frequency on the oocyte membrane surface, and have not previously been seen using other isolation and imaging methods. Histogram analysis of the center-to-center distance between LAPs suggest their size to be about 44 nm in diameter, considerably larger than other reported size estimates of IMPs. These results indicate that LAPs represent a novel membrane particle organization, which merits further study.; Future developments using this method or further studies to develop alternative membrane preparations may help elucidate membrane protein structure.