Hanson, B.R., Runft, D.L., Streeter, C., Kumar, A., Carion, T.W., and Neely, M.N. (2012) Functional analysis of the CpsA protein of Streptococcus agalactiae. Journal of bacteriology. 194(7):1668-1678.
Streptococcal pathogens such as Streptococcus agalactiae (GBS) 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 wild type, and demonstrated that production of full length CpsA or the DNA-binding region
of CpsA resulted in increased capsule levels. In contrast, 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, were 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.
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