THE REGION OF HUMAN TRANSFERRIN INVOLVED IN BINDING TO BACTERIAL TRANSFERRIN RECEPTORS IS LOCALIZED IN THE C-LOBE

Iron-saturated human transferrin was digested with either chymotrypsin or trypsin to produce C-lobe and N-lobe protein fragments. Individual protein fragments were purified by a combination of gel filtration an d Concanavalin A affinity chromatographic procedures. The C-lobe and N -lobe fragments of human transferrin were then used in binding assays to assess their ability in binding to the bacterial transferrin recept ors. Competitive binding assays demonstrated that the C-lobe fragment of human transferrin binds as well as intact human transferrin to bact erial transferrin receptors from Neisseria meningitidis, Neisseria gon orrhoeae and Haemophilus influenzae. Using isogenic mutants of N. meni ngitidis deficient in either of the transferrin-binding proteins (Tbps ), we demonstrated that both transferrin-binding proteins were able to bind to the C-lobe fragment of human transferrin.