An Enterococcus faecium secreted antigen, SagA, exhibits broad-spectrum binding to extracellular matrix proteins and appears essential for E. faecium growth.

TitleAn Enterococcus faecium secreted antigen, SagA, exhibits broad-spectrum binding to extracellular matrix proteins and appears essential for E. faecium growth.
Publication TypeJournal Article
Year of Publication2003
AuthorsTeng, F, Kawalec, M, Weinstock, GM, Hryniewicz, W, Murray, BE
JournalInfect Immun
Volume71
Issue9
Pagination5033-41
Date Published2003 Sep
ISSN0019-9567
KeywordsAmino Acid Sequence, Antigens, Bacterial, Bacterial Proteins, Base Sequence, Chromosome Mapping, DNA, Bacterial, Enterococcus faecium, Extracellular Matrix Proteins, Fibrinogen, Genes, Bacterial, Humans, Molecular Sequence Data, Protein Binding, Recombinant Proteins, Virulence
Abstract

A gene encoding a major secreted antigen, SagA, was identified in Enterococcus faecium by screening an E. faecium genomic expression library with sera from patients with E. faecium-associated endocarditis. Recombinant SagA protein showed broad-spectrum binding to extracellular matrix (ECM) proteins, including fibrinogen, collagen type I, collagen type IV, fibronectin, and laminin. A fibrinogen-binding protein, purified from culture supernatants of an E. faecium clinical isolate, was found to match the N-terminal sequence of the predicted SagA protein and to react with the anti-SagA antibody, confirming that it was the SagA protein; this protein appeared as an 80- to 90-kDa smear on a Western blot that was sensitive to proteinase K and resistant to periodate treatment and glycoprotein staining. When overexpressed in E. faecium and Escherichia coli, the native and recombinant SagA proteins formed stable oligomers, apparently via their C-terminal domains. The SagA protein is composed of three domains: (i) a putative coiled-coil N-terminal domain that shows homology to the N-terminal domain of Streptococcus mutans SagA protein (42% similarity), previously shown to be involved in cell wall integrity and cell shape maintenance, and to the P45 protein of Listeria monocytogenes (41% similarity); (ii) a central domain containing direct repeats; and (iii) a C-terminal domain that is similar to that found in various proteins, including P45 (50% similarity) and P60 (52% similarity) of L. monocytogenes. The P45 and P60 proteins both have cell wall hydrolase activity, and the latter has also been shown to be involved in virulence, whereas cell wall hydrolase activity was not detected for SagA protein. The E. faecium sagA gene, like the S. mutans homologue, is located in a cluster of genes encoding proteins that appear to be involved in cell wall metabolism and could not be disrupted unless it was first transcomplemented, suggesting that the sagA gene is essential for E. faecium growth and may be involved in cell wall metabolism. In conclusion, the extracelluar E. faecium SagA protein is apparently essential for growth, shows broad-spectrum binding to ECM proteins, forms oligomers, and is antigenic during infection.

Alternate JournalInfect. Immun.
PubMed ID12933846
PubMed Central IDPMC187350
Grant ListR01 AI042399 / AI / NIAID NIH HHS / United States
R56 AI042399 / AI / NIAID NIH HHS / United States
AI42399 / AI / NIAID NIH HHS / United States