Salmonellae survive and propagate in macrophages to cause serious systemic disease. Periplasmic
superoxide dismutase plays a critical role in this survival by combating phagocytic
superoxide. Salmonella Typhimurium strain 14028 produces two periplasmic
superoxide dismutases: SodCI and SodCII. Although both
proteins are produced during
infection, only SodCI is functional in the macrophage phagosome. We have previously shown that SodCI, relative to SodCII, is both
protease resistant and tethered within the periplasm and that either of these properties is sufficient to allow a SodC to protect against phagocytic
superoxide. Tethering is defined as remaining cell-associated after osmotic shock or treatment with
cationic antimicrobial peptides. Here we show that SodCI non-covalently binds
peptidoglycan. SodCI binds to Salmonella and Bacillus
peptidoglycan, but not
peptidoglycan from Staphylococcus. Moreover, binding can be inhibited by a
diaminopimelic acid containing tripeptide, but not a
lysine containing tripeptide, showing that the
protein recognizes the
peptide portion of the
peptidoglycan. Replacing nine
amino acids in SodCII with the corresponding residues from SodCI confers tethering, partially delineating an apparently novel
peptidoglycan binding domain. These changes in sequence increase the affinity of SodCII for
peptidoglycan fragments to match that of SodCI and allow the now tethered SodCII to function during
infection.