Streptococcus mutans YidC1 and YidC2 affect P1 surface immunoreactivity/function

Streptococcus mutans encodes two paralogs of the bacterial membrane-localized chaperone YidC.  Removal of yidC2, but not yidC1 results in stress-sensitivity similar to that observed following disruption of the co-translational signal recognition particle protein translocation pathway.  This phenotype is contributed to by the charged C-terminal tail of YidC2.  A similar domain in the Saccharomyces cervisiae ortholog oxa1 binds mitochondrial ribosomes.  Objectives: The current study evaluated the effects of elimination of YidC1, YidC2, or the C-terminus of YidC2 on surface localization and function of adhesin P1 (Antigen I/II), predicted to be secreted post-translationally via the general secretion pathway.   Methods: Chromosomal DNA encoding YidC1, YidC2 or the C-terminus of YidC2 was eliminated.  Mutants were tested by dot blot for immunoreactivity with anti-P1 polyclonal and seven different monoclonal antibodies, for binding to immobilized salivary agglutinin (SAG) by BiaCore assay, and for aggregation by fluid-phase SAG.  Complementation of ΔyidC2 by plasmid-encoded E.coli yidC or yeast oxa1 or oxa2 was also tested.  Results: S. mutans NG8 ΔyidC2 (but not yidC2ΔC) demonstrated decreased immunoreactivity with all Abs.  The effect was more pronounced with several MAbs recognizing conformationally-dependent epitopes.  The ΔyidC1 strain demonstrated increased immunoreactivity with all Abs tested.  Adherence was increased in the ΔyidC1, decreased in the ΔyidC2, and unaltered in the yidC2ΔC strains.  Slight loss of SAG-mediated aggregation was observed for all three mutants.  Yeast oxa1 and oxa2 fully restored Ab reactivity and partially rescued adherence of the ΔyidC2 strain, whereas E.coli yidC further decreased immunoreactivity and did not restore adherence.  Yeast oxa2, but not oxa1, restored S. mutans ΔyidC2 aggregation, whereas E. coli yidC further decreased aggregation.  Conclusions: Results are consistent with a balanced surface biogenesis mechanism involving both YidC1 and YidC2 that contributes to P1 quantity, maturation and functional activity that is complemented or exacerbated to varying degrees by yidC, oxa1 or oxa2.  (NIH-R01DE08007)