Protonation state of Asp (Glu)-85 regulates the purple-to-blue transition in bacteriorhodopsin mutants Arg-82----Ala and Asp-85----Glu: The blue form is inactive in proton translocation
- Massachusetts Institute of Technology, Cambridge (USA)
Previous studies with site-specific mutants of bacteriorhodopsin have demonstrated that replacement of Asp-85 or Arg-82 affects the absorption spectrum. Between pH 5.5 and 7, the Asp-85----Glu and Arg-82----Ala mutants exist in a pH-dependent equilibrium between purple (lambda max approximately 550/540 nm) and blue (lambda max approximately 600/590 nm) forms of the pigment. Measurement of proton transport as a function of wavelength in reconstituted vesicles shows that proton-pumping activities for the above mutants reside exclusively in their respective purple species. For both mutants, formation of the blue form with decreasing pH is accompanied by loss of proton transport activity. The Asp-85----Asn mutant displays a blue chromophore (lambda max approximately 588 nm), is inactive in proton translocation from pH 5 to 7.5, and shows no transition to the purple form. In contrast, the Asp-212----Asn mutant is purple (lambda max approximately 555 nm) and shows no transition to a blue chromophore with decreasing pH. The experiments suggest that (i) the pKa of the purple-to-blue transition is directly influenced by the pKa of the carboxylate at residue 85 and (ii) the relative strengths of interaction between the protonated Schiff base, Asp-85, Asp-212, and Arg-82 make a major contribution to the regulation of color and function of bacteriorhodopsin.
- OSTI ID:
- 7192263
- Journal Information:
- Proceedings of the National Academy of Sciences of the United States of America; (USA), Journal Name: Proceedings of the National Academy of Sciences of the United States of America; (USA) Vol. 87:3; ISSN 0027-8424; ISSN PNASA
- Country of Publication:
- United States
- Language:
- English
Similar Records
Substitution of amino acids Asp-85, Asp-212, and Arg-82 in bacteriorhodopsin affects the proton release phase of the pump and the pK of the Schiff base
Structure-function studies on bacteriorhodopsin. X. Individual substitutions of arginine residues by glutamine affect chromophore formation, photocycle, and proton translocation
Related Subjects
59 BASIC BIOLOGICAL SCIENCES
ABSORPTION SPECTRA
ALANINES
AMINO ACIDS
ARGININE
ASPARTIC ACID
BARYONS
CARBOXYLIC ACIDS
ELEMENTARY PARTICLES
FERMIONS
GLUTAMIC ACID
HADRONS
IMINES
MUTATIONS
NUCLEONS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PH VALUE
PIGMENTS
PROTEINS
PROTONS
RHODOPSIN
SCHIFF BASES
SPECTRA
SPECTROPHOTOMETRY
TRANSLOCATION