Bacteriorhodopsin fusion membrane protein expression system

An expression vector comprising:

• a) a polynucleotide sequence encoding a mutant bacteriorhodopsin having at least 80% sequence identity to SEQ ID NO:
• 1;
• b) a multiple cloning site, located downstream from the polynucleotide encoding the mutant bacteriorhodopsin;
• c) a T7 promoter, operably linked to the polynucleotide sequence encoding the mutant bacteriorhodopsin,
• d) a nucleic acid sequence encoding a polyhistidine tag, located downstream from the polynucleotide sequence encoding the mutant bacteriorhodopsin and upstream from the multiple cloning site;
• e) a first polynucleic acid encoding a first protease cleavage site, located downstream from the nucleic acid sequence encoding the polyhistidine tag and upstream from the multiple cloning site;
• f) optionally a second polynucleic acid encoding a second protease cleavage site, located between the polynucleotide sequence encoding the mutant bacteriorhodopsin and the nucleic acid sequence encoding the polyhistidine tag;
• and
• g) optionally a nucleotide sequence encoding a linker located between the first polynucleic acid encoding the first protease cleavage site and the multiple cloning site;
• wherein the mutant bacteriorhodopsin retains Asn94 of SEQ ID NO:
• 1.