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

Journal Article · Thu Feb 01 00:00:00 EST 1990 · Proceedings of the National Academy of Sciences of the United States of America; (USA)

DOI:https://doi.org/10.1073/pnas.87.3.1013· OSTI ID:7192263

Subramaniam, S; Marti, T; Khorana, H G ^[1]

---

1. 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), Vol. 87:3; ISSN 0027-8424
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
PROTONS
TRANSLOCATION
RHODOPSIN
ABSORPTION SPECTRA
ALANINES
ARGININE
ASPARTIC ACID
GLUTAMIC ACID
MUTATIONS
PH VALUE
SCHIFF BASES
SPECTROPHOTOMETRY
AMINO ACIDS
BARYONS
CARBOXYLIC ACIDS
ELEMENTARY PARTICLES
FERMIONS
HADRONS
IMINES
NUCLEONS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PIGMENTS
PROTEINS
SPECTRA
550200* - Biochemistry