IDENTIFICATION OF A TRANSFERRIN-BINDING PROTEIN FROM BORRELIA-BURGDORFERI

Bacterial pathogens have evolved various strategies to acquire iron fr om the iron-restricted environment found in mammalian hosts. Borrelia burgdorferi should be no different with regard to its requirement for ferric iron, and previous studies have suggested that transferrin (Tf) may be a source of iron in vivo. By probing blots with Tf conjugated to horseradish peroxidase, we have identified an outer membrane protei n (28 kDa) from B. burgdorferi B31 that bound holo-Tf but not apo-Tf. The 28-kDa protein bound human, rat, or mouse Tf and was produced only by low-passage (less than passage 5), virulent isolates of strain B31 . In addition, the Tf-binding protein (Tbp) from strain B31 retained t he ability to bind Tf after treatment with 2% sodium dodecyl sulfate-1 % beta-mercaptoethanol and heating to 100 degrees C for 5 min. These p roperties are remarkably similar to those of the Tbp of Staphylococcus aureus and Tbp2 from Neisseria meningitidis, B. burgdorferi Sh-2-82 p roduced an outer membrane protein different in size, i.e., 26 kDa, but with properties similar to those of to the protein from strain B31, s uggesting variation in B. burgdorferi Tbps. The exact role of the 28-k Da protein in iron acquisition by B. burgdorferi remains to be determi ned.