STRUCTURE OF THE MYCOBACTERIUM-TUBERCULOSIS ANTIGEN-88, A PROTEIN RELATED TO THE ESCHERICHIA-COLI PSTA PERIPLASMIC PHOSPHATE PERMEASE SUBUNIT

We report the cloning and sequencing of the gene coding for antigen 88 from Mycobacterium tuberculosis by using monoclonal antibodies to screen an expression library in lambda gt11. The gene encodes a 403-amino-acid-residue protein,vith a calculated molecular mass of 43,790 Da which contains seven putative transmembrane or-helical domains and presents a significant homology to the PstA protein of Escherichia coli. In its N-terminal region, it contains a 61-amino-acid region highly homologous to the fifth transmembrane helix off. E coli PstC. PstA and PstC are the two hydrophobic subunits of an E. coli periplasmic phosphate permease. Since the phosphate-binding subunit of this putative permease in M. tuberculosis has previously been characterized, i.e., the 38-kDa mycobacterial protein (also called protein antigen b, Ag 5, and Ag 78) homologous to PstS off E. coli, it seems likely that functional permeases analogous to the periplasmic permeases of gram-negative bacteria also exist in mycobacteria.