Saliva-binding protein (SsaB) from Streptococcus sanguis 12 is a lipoprotein

Two lipoprotein consensus sequences (Leu-X-X-Cys) are found in the presumptive signal peptide region (positions 12 to 15 and 17 to 20) of saliva-binding protein (SsaB) from Streptococcus sanguis 12. Three analogs of SsaB containing Cys-->Gly mutations were constructed by site-directed mutagenesis of pSA2, the recombinant plasmid expressing SsaB. [3H]palmitate was incorporated into SsaB only when the native Cys-20 residue was present. These data show that SsaB is a lipoprotein and that Cys-20 is the critical site for acylation.