Opening the Schiff base moiety of bacteriorhodopsin by mutation of the four extracellular Glu side chains

• Published in: FEBS letters Vol. 456; no. 1; pp. 191 - 195
• Main Authors: Sanz, Carolina, Lazarova, Tzvetana, Sepulcre, Francesc, González-Moreno, Rafael, Bourdelande, José-Luis, Querol, Enric, Padrós, Esteve
• Format: Journal Article
• Language: English
• Published: England Elsevier B.V 30.07.1999
• Subjects: 4Glu, the bacteriorhodopsin mutant E9Q+E74Q+E194Q+E204Q; Bacteriorhodopsin; Bacteriorhodopsins - chemistry; Bacteriorhodopsins - genetics; BR, bacteriorhodopsin; Darkness; E9Q+E74Q+E194Q+E204Q mutant; Extracellular structure; Glutamic Acid - chemistry; Hydrogen-Ion Concentration; Hydroxylamine - chemistry; Hydroxylamine accessibility; Kinetics; Light; Mutagenesis, Site-Directed; Mutation; Salts; Schiff Bases; Spectrum Analysis; Bacteriorhodopsin; Extracellular structure; 4Glu, the bacteriorhodopsin mutant E9Q+E74Q+E194Q+E204Q; BR, bacteriorhodopsin; Hydroxylamine accessibility; E9Q+E74Q+E194Q+E204Q mutant
• ISSN: 0014-5793; 1873-3468
• DOI: 10.1016/S0014-5793(99)00950-3

The quadruple bacteriorhodopsin (BR) mutant E9Q+E74Q+E194Q+E204Q shows a λ max of about 500 nm in water at neutral pH and a great influence of pH and salts on the visible absorption spectrum. Accessibility to the Schiff base is strongly increased, as detected by the rapid bleaching effect of hydroxylamine in the dark as well as in light. Both the proton release kinetics and the photocycle are altered, as indicated by a delayed proton release after proton uptake and changed M kinetics. Moreover, affinity of the color-controlling cation(s) is found to be decreased. We suggest that the four Glu side chains are essential elements of the extracellular structure of BR.