title: Role of the cell wall microenvironment in expression of a heterologous SpaP-S1 fusion protein by Streptococcus gordonii.
abstract: The charge density in the cell wall microenvironment of Gram-positive bacteria is believed to influence the expression of heterologous proteins. To test this, the expression of a SpaP-S1 fusion protein, consisting of the surface protein SpaP of Streptococcus mutans and a pertussis toxin S1 fragment, was studied in the live vaccine candidate bacterium Streptococcus gordonii. Results showed that the parent strain PM14 expressed very low levels of SpaP-S1. By comparison, the dlt mutant strain, which has a mutation in the dlt operon preventing d-alanylation of the cell wall lipoteichoic acids, and another mutant strain, OB219(pPM14), which lacks the LPXTG major surface proteins SspA and SspB, expressed more SpaP-S1 than the parent. Both the dlt mutant and the OB219(pPM14) strain had a more negatively charged cell surface than PM14, suggesting that the negative charged cell wall played a role in the increase in SpaP-S1 production. Accordingly, the addition of Ca(2+), Mg(2+), and K(+), presumably increasing the positive charge of the cell wall, led to a reduction in SpaP-S1 production, while the addition of bicarbonate resulted in an increase in SpaP-S1 production. The level of SpaP-S1 production could be correlated with the level of PrsA, a peptidyl-prolyl cis/trans isomerase, in the cells. PrsA expression appears to be regulated by the cell envelope stress two-component regulatory system LiaSR. The results collectively indicate that the charge density of the cell wall microenvironment can modulate heterologous SpaP-S1 protein expression in S. gordonii and that this modulation is mediated by the level of PrsA, whose expression is regulated by the LiaSR two-component regulatory system.
authors.affiliation: Dept. of Applied Oral Sciences, Faculty of Dentistry, Dalhousie University, Halifax, Nova Scotia, Canada B3H 3J5.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Davis
authors.forename: Dustin
authors.initials: D
authors.lastname: Kennedy
authors.forename: Scott A
authors.initials: SA
authors.lastname: Halperin
authors.forename: Song F
authors.initials: SF
authors.lastname: Lee
mesh_terms: D002412:Cations / Q000378:metabolism; D002473:Cell Wall / Q000737:chemistry / Q000378:metabolism*; D015870:Gene Expression; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008670:Metals / Q000378:metabolism; D037342:Pertussis Toxin / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D055672:Static Electricity; D054773:Streptococcus gordonii / Q000235:genetics / Q000378:metabolism*; D013499:Surface Properties
chemical_list: D002412:Cations; D008565:Membrane Proteins; D008670:Metals; D011994:Recombinant Proteins; C083388:pertussis toxin, S1 subunit; D037342:Pertussis Toxin