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Journal of Biomedicine and Biotechnology
Volume 2010, Article ID 956071, 16 pages
Review Article

The Structure and Function of Serum Opacity Factor: A Unique Streptococcal Virulence Determinant That Targets High-Density Lipoproteins

1Veterans Affairs Medical Center and Department of Medicine, University of Tennessee Health Science Center, 1030 Jefferson Avenue, Memphis, TN 38104, USA
2Department of Medicine, Baylor College of Medicine, Houston, TX 77030, USA

Received 9 April 2010; Accepted 26 May 2010

Academic Editor: Mari A. Smits

Copyright © 2010 Harry S. Courtney and Henry J. Pownall. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Serum opacity factor (SOF) is a virulence determinant expressed by a variety of streptococcal and staphylococcal species including both human and animal pathogens. SOF derives its name from its ability to opacify serum where it targets and disrupts the structure of high-density lipoproteins resulting in formation of large lipid vesicles that cause the serum to become cloudy. SOF is a multifunctional protein and in addition to its opacification activity, it binds to a number of host proteins that mediate adhesion of streptococci to host cells, and it plays a role in resistance to phagocytosis in human blood. This article will provide an overview of the structure and function of SOF, its role in the pathogenesis of streptococcal infections, its vaccine potential, its prevalence and distribution in bacteria, and the molecular mechanism whereby SOF opacifies serum and how an understanding of this mechanism may lead to therapies for reducing high-cholesterol concentrations in blood, a major risk factor for cardiovascular disease.