CLONING, SEQUENCING, AND EXPRESSION IN ESCHERICHIA-COLI OF OXLT, THE OXALATE, FORMATE EXCHANGE PROTEIN OF OXALOBACTER-FORMIGENES

OxlT is the oxalate/formate exchange protein that represents the vecto rial component of a proton-motive metabolic cycle in Oxalobacter formi genes. Here we report the cloning and sequencing of OxlT and describe its expression in Escherichia coli. The OxlT amino acid sequence speci fies a polytopic hydrophobic protein of 418 residues with a mass of 44 ,128 daltons. Analysis of hydropathy and consideration of the distribu tion of charged residues suggests an OxlT secondary structure having 1 2 transmembrane segments, oriented so that the N and C termini face th e cytoplasm. Expression of OxlT in E. coli coincides with appearance o f a capacity to carry out the self-exchange of oxalate and the heterol ogous, electrogenic exchange of oxalate with formate. The unusually hi gh velocity of OxlT-mediated transport is also preserved in E. coli. W e conclude that the essential features of OxlT are retained on its exp ression in E. coli.