Gaoyan (Grace) Tang-Siegel, Ph.D.
I received my PhD in the field of oral microbiology from the University of Hong Kong in 2004. I had my postdoctoral training in microbiology and molecular genetics from the University of Vermont; and continued to work in the field of bacteriology and genetics in the University of Southern California, before I joined the Department of Molecular Physiology and Biophysics, College of Medicine as a faculty scientist in 2016.
The gram-negative, non-motile, capnophilic bacterium Aggregatibacter actinomycetemcomitans is a recognized oropharyngeal colonizer, found in the oral cavity of 20% of the population. A. actinomycetemcomitans potentially causes aggressive periodontitis and/or systemic infections, including infective endocarditis and pulmonary infections. Multiple virulence factors are involved during the progress of infection by A. actinomycetemcomitans, and collagen adhesin EmaA (extracellular matrix adhesin A) is one of the important determinants during the early stage of the infection.
Our early work demonstrated that the adhesin EmaA facilitates A. actinomycetemcomitans bind to collagen. Collagen is the most abundant protein in humans, and the major component found in the periodontal tissue and heart valves. The EmaA adhesin is a trimeric, 606 kDa protein that forms an antenna-like appendage protruding from the bacterial surface. Interestingly, EmaAs are glycosylated using the same mechanism that the O-polysaccharide (O-PS) sugars are added to the lipopolysaccharide (LPS), a novel post-translational modification; and the glycosylation is important for maintaining the function of the EmaA as an adhesin, as well as maintaining the stability of the EmaA structure.
Currently, we are interested at understating precisely how glycosylation affects the structure and/or conformation changes of EmaAs during binding; and how different sugars found in the EmaA structures, which are determined by different serotypes of A. actinomycetemcomitans, may change the efficiency of binding.
Faculty Highlighted Publications
Tang-Siegel G., Bumgarner R., Ruiz T., Kittichotirat W., Chen W. & Chen. C. (2016). Human-serum specific activation of alternative sigma factors, the stress responders in Aggregatibacter actinomycetemcomitans PLoS One 11:e0160018. doi: 10.1371/journal.pone.0160018. (PMID: 27490177; PMCID: PMC4973924).
Tang G., Ruiz T. & Mintz K. P. (2012). O-polysaccharide glycosylation is required for stability and function of the collagen adhesin EmaA of Aggregatibacter actinomycetemcomitans Infect Immun 80:2868-2877. (PMID: 22689812; PMC3434563).
Tang G., Kawai T., Komatsuzawa H. & Mintz K. P. (2012). Lipopolysacachirdes mediate leukotoxin secretion in Aggregatibacter actinomycetemcomitans. Mol Oral Microbiol 27: 70-82. (PMID: 22394466; PMC3296970).
Tang G. & Mintz K. P. (2010). Glycosylation of the collagen adhesin EmaA of Aggregatibacter actinomycetemcomitans is dependent upon the lipopolysaccharide biosynthetic pathway. J Bacteriol 192:1395-1404. (PMID: 20061477; PMC2820841).
Tang G., Kitten T., Munro C. L., Wellman G. C. & Mintz K. P. (2008). EmaA, a potential virulence determinant of Aggregatibacter actinomycetemcomitans in infective endocarditis. Infect Immun 76:2316-2324. (PMID: 18347033; PMC2423096).
National Institute of Health (NIH) training grant R90 DE22528-3 in Bacteriology, University of Southern California, Los Angeles, CA. 2013-2015