Structural analysis of human and bovine .alpha.-fetoprotein by electron microscopy, image processing, and circular dichroism

Publisher Website
Google Scholar
Abstract
The images of human and bovine .alpha.-fetoprotein molecules were enhanced by combining dark-field EM with a laser-assisted optical system. This system filters out random background noise while permitting true averaged signal reconstruction of the molecule. A single averaged molecular image was digitized into a matrix, each pixel being assigned a gray scale level to produce a relative mass map for each molecule. These maps were interpreted from the .alpha.-helix, .beta.-form and random coil of the purified proteins as determined by circular dichroism (CD). Results showed that both molecules are U-shaped apparently monomeric, with outside dimensions of .apprx. 80 .ANG.. Both molecules have asymmetrical structural features, notably 3 mass dense regions at both extremities and at the vertex of the molecules. CD data suggest a high degree of similar stabilized .alpha.-helix and extensive .beta.-form in these regions. Mass map analysis of human .alpha.-fetoprotein correlates with the subdomains organized by disulfide bridges.