The gene encoding gp63, the major surface glycoprotein of Leishmania promastigotes, was isolated from Leishmania major using a synthetic oligonucleotide probe based on the NH2-terminal protein sequence of purified gp63. DNA sequence analysis and the translated amino acid sequence indicate that gp63 is synthesized as precursor molecule having both an NH2-terminal preregion (signal peptide) and an adjacent proregion. This structure is consistent with the protease activity of gp63 since many other proteases are synthesized as precursor forms requiring processing for enzymatic activity. Hybridization studies demonstrated that there are multiple copies of the gp63 gene in the genome of L. major and other Leishmania species. The conservation of the coding sequence of gp63 amongst diverse species of Leishmania provides further support for the importance of gp63 during the life cycle of Leishmania.
Pathogenic bacteria in the Neisseriaceae and Pasteurellaceae possess outer membrane proteins that specifically bind transferrin from the host as the first step in the iron acquisition process. As a logical progression from prior studies of the ligand-receptor interaction using biochemical approaches, we have initiated an approach involving the production of recombinant chimeric transferrins to further identify the regions of transferrin involved in receptor binding. In order to prepare bovine/human hybrids, the bovine transferrin gene was cloned, sequenced, and compared with the existing human transferrin gene sequence. After identification of potential splice sites, hybrid transferrin genes were constructed using the polymerase chain reaction-based approach of splicing by overlap extension. Five hybrid genes containing sequences from both bovine and human transferrin were constructed. Recombinant transferrins were produced in a baculovirus expression vector system and affinity-purified using concanavalin A-Sepharose. The recombinant proteins were analyzed for reactivity against polyclonal and monoclonal antibodies and assessed for binding to Neisseria meningitidis transferrin receptor proteins in solidphase binding assays and affinity isolation experiments. These experiments enabled us to localize the regions of human transferrin predominantly involved in binding to the N. meningitidis receptor to amino acid residues 346 -588. The construction of these chimeras provides unique tools for the investigation of transferrin binding to receptors from both human and bovine bacterial pathogens.
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