Distinct affinity of binding sites for S-layer homologous domains in Clostridium thermocellum and Bacillus anthracis cell envelopes

Binding parameters were determined for the SLH (S-layer homologous) domains from the Clostridium thermocellum outer layer protein OlpB, from the C. th ermocellum S-layer protein SlpA, and from the Bacillus anthracis S-layer pr oteins EA1 and Sap, using cell walls from C. thermocellum and B. anthracis, Each SLH domain bound to C. thermocellum and B. anthracis cell walls with a different K-D, ranging between 7.1 x 10(-7) and 1.8 x 10(-8) M. Cell wall binding sites for SLH domains displayed different binding specificities in C. thermocellum and B. anthracis, SLH-binding sites were not detected in c ell walls of Bacillus subtilis. Cell walls of C. thermocellum lost their af finity for SLH domains after treatment with 48% hydrofluoric acid but not a fter treatment with formamide or dilute acid. A soluble component, extracte d from C. thermocellum cells by sodium dodecyl sulfate treatment, bound the SLH domains from C. thermocellum but not those from B, anthracis proteins. A corresponding component was not found in B. anthracis.