BIOCHEMICAL-ANALYSIS OF LACTOFERRIN RECEPTORS IN THE NEISSERIACEAE - IDENTIFICATION OF A 2ND BACTERIAL LACTOFERRIN RECEPTOR PROTEIN

Bacterial transferrin receptors that have been described in the famili es Pasteurellaceae and Neisseriaceae are composed of two receptor prot eins, transferrin binding proteins 1 and 2 (Tbp1 and Tbp2). In contras t, bacterial lactoferrin receptors have only been described for human pathogens in the family Neisseriaceae, and were believed to consist of a single protein, Lbp1,which is highly homologous to Tbp1. We describ e a modified affinity isolation procedure that facilities isolation of a second lactoferrin receptor protein Lbp2 (a presumptive Tbp2 homolo gue) from Neisseria meningitidis, Moraxella catarrhalis and Moraxella bovis using immobilized lactoferrin. Antiserum specific for either the M. catarrhalis Tbp1+2 molecules, the M. catarrhalis Lbp1 molecule, or for a commercial preparation of human lactoferrin did not react on we stern blots with the same organisms' affinity purified Lbp2. In additi on, the M. catarrhalis Lbp2 could be isolated in a functional form wit hout contaminating Lbp1 or Tbp1+2. We also demonstrate that the bovine pathogen, M. bovis, produces functional transferrin and lactoferrin r eceptors specific for the bovine forms of these glycoproteins. A putat ive IbpB gene, recently speculated to reside immediately upstream of t he N. meningitidis Lbp1 structural gene, IbpA, likely encodes the newl y isolated Lbp2 protein from this bacterial species. (C) 1995 Academic Press Limited