Functional Analysis of the CpsA Protein of Streptococcus agalactiae

• Published in: Journal of Bacteriology 2012-04, Vol.194 (7), p.1668-1678
• Main Authors: Hanson, Brett R, Runft, Donna L, Streeter, Cale, Kumar, Abhin, Carion, Thomas W, Neely, Melody N
• Format: Article
• Language: English
• Subjects: Animals; Bacterial Capsules - biosynthesis; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacteriology; Binding sites; Biological and medical sciences; blood; cell walls; Danio rerio; Deoxyribonucleic acid; DNA; Erythrocytes - microbiology; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Bacterial; Gram-positive bacteria; Humans; loci; lysozyme; Microbiology; Miscellaneous; Operon; Pathogens; Promoter Regions, Genetic; Protein Binding; Protein Structure, Tertiary; Proteins; Streptococcal Infections - microbiology; Streptococcus agalactiae; Streptococcus agalactiae - chemistry; Streptococcus agalactiae - genetics; Streptococcus agalactiae - metabolism; Streptococcus agalactiae - pathogenicity; transcription factors; Virulence; Zebrafish
• ISSN: 0021-9193; 1098-5530; 1067-8832
• DOI: 10.1128/jb.06373-11

Streptococcal pathogens, such as the group B streptococcus (GBS) Streptococcus agalactiae, are an important cause of systemic disease, which is facilitated in part by the presence of a polysaccharide capsule. The CpsA protein is a putative transcriptional regulator of the capsule locus, but its exact contribution to regulation is unknown. To address the role of CpsA in regulation, full-length GBS CpsA and two truncated forms of the protein were purified and analyzed for DNA-binding ability. Assays demonstrated that CpsA is able to bind specifically to two putative promoters within the capsule operon with similar affinity, and full-length protein is required for specificity. Functional characterization of CpsA confirmed that the ΔcpsA strain produced less capsule than did the wild type and demonstrated that the production of full-length CpsA or the DNA-binding region of CpsA resulted in increased capsule levels. In contrast, the production of a truncated form of CpsA lacking the extracellular LytR domain (CpsA-245) in the wild-type background resulted in a dominant-negative decrease in capsule production. GBS expressing CpsA-245, but not the ΔcpsA strain, was attenuated in human whole blood. However, the ΔcpsA strain showed significant attenuation in a zebrafish infection model. Furthermore, chain length was observed to be variable in a CpsA-dependent manner, but could be restored to wild-type levels when grown with lysozyme. Taken together, these results suggest that CpsA is a modular protein influencing multiple regulatory functions that may include not only capsule synthesis but also cell wall associated factors.