期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1981
卷号：78
期号：8
页码：4689-4693
DOI：10.1073/pnas.78.8.4689
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The conformation and molecular dimensions of purified type 6 streptococcal M proteins establish the close structural relationship of these molecules to tropomyosin. Ultracentrifuge studies reveal that the M molecules exist as stable dimers; circular dichroism spectra indicate that the molecules contain about 70% alpha helix; and fiber x-ray diffraction diagrams show the characteristic reflections of the alpha-helical pattern. Electron microscopic images of M protein shadowed with platinum reveal rod-shaped molecules having the same width as tropomyosin. However, the lengths of the M molecules are about 30% shorter than lengths predicted by assuming a completely alpha-helical molecule. These findings indicate that the structure of the M6 protein is primarily alpha-helical coiled coil. Comparison of the lengths of the fibers on the surface of the streptococcus and the isolated M proteins suggests that each fiber on the cell wall consists of a single M-protein molecule approximately 500 A long. The structure determined for these fimbriae is the first alpha-helical coiled-coil conformation to be demonstrated for bacterial surface projections.
