Description:
<jats:title>ABSTRACT</jats:title>
<jats:p>
The SraP adhesin of
<jats:italic>Staphylococcus aureus</jats:italic>
is a member of a highly conserved family of serine-rich surface glycoproteins of gram-positive bacteria. For streptococci, export of the SraP homologs requires a specialized transport pathway (the accessory Sec system). Compared to streptococci, however, SraP is predicted to differ in its signal peptide and glycosylation, which may affect its dependence on a specialized system for transport. In addition, two genes (
<jats:italic>asp4</jats:italic>
and
<jats:italic>asp5</jats:italic>
) essential for export in
<jats:italic>Streptococcus gordonii</jats:italic>
are missing in
<jats:italic>S. aureus</jats:italic>
. Thus, the selectivity of the accessory Sec system in
<jats:italic>S. aureus</jats:italic>
may also differ compared to streptococci. To address these issues, the five genes encoding the putative accessory Sec system (
<jats:italic>secY2</jats:italic>
,
<jats:italic>secA2</jats:italic>
, and
<jats:italic>asp1-3</jats:italic>
) were disrupted individually in
<jats:italic>S. aureus</jats:italic>
ISP479C, and the resultant mutants were examined for SraP export. Disruption of
<jats:italic>secA2</jats:italic>
resulted in the near complete loss of SraP surface expression. Similar results were seen with disruption of
<jats:italic>secY2</jats:italic>
and
<jats:italic>asp1</jats:italic>
,
<jats:italic>asp2</jats:italic>
, or
<jats:italic>asp3</jats:italic>
. To assess whether the accessory Sec system transported other substrates, we compared secreted proteomes of ISP479C and a
<jats:italic>secA2</jats:italic>
isogenic mutant, by two-dimensional fluorescence difference gel electrophoresis. Although two consistent differences in proteome content were noted between the strains, neither protein appeared to be a likely substrate for accessory Sec export. Thus, the accessory Sec system of
<jats:italic>S. aureus</jats:italic>
is required for the export of SraP, and it appears to be dedicated to the transport of this substrate exclusively.
</jats:p>