Histidine residues regulate the transition of photoexcited rhodopsin to its active conformation, metarhodopsin II

Neuron. 1992 Mar;8(3):465-72. doi: 10.1016/0896-6273(92)90274-h.


The biologically active photoproduct of rhodopsin, metarhodopsin II (M II), exists in a pH-sensitive equilibrium with its precursor, metarhodopsin I (M I). Increasing acidity favors M II, with the midpoint of the pH titration curve at pH 6.4. To test the long-standing proposal that histidine protonation regulates this conformational transition, we characterized mutant rhodopsins in which each of the 6 histidines was replaced by phenylalanine or cysteine. Only mutants substituted at the 3 conserved histidines showed abnormal M I-M II equilibria. Those in which His-211 was replaced by phenylalanine or cysteine formed little or no M II at either extreme of pH, whereas mutants substituted at His-65 or at His-152 showed enhanced sensitivity to protons. The simplest interpretation of these results is that His-211 is the site where protonation strongly stabilizes the M II conformation and that His-65 and His-152 are sites where protonation modestly destabilizes the M II conformation.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Cattle
  • DNA Mutational Analysis
  • Digitonin
  • Eye Proteins / chemistry
  • Histidine / chemistry
  • Hydrogen-Ion Concentration
  • Molecular Sequence Data
  • Peptides / chemistry
  • Photochemistry
  • Recombinant Proteins / chemistry
  • Rhodopsin / analogs & derivatives*
  • Rhodopsin / chemistry*
  • Rod Opsins
  • Solubility
  • Spectrum Analysis


  • Eye Proteins
  • Peptides
  • Recombinant Proteins
  • Rod Opsins
  • Histidine
  • metarhodopsins
  • Rhodopsin
  • Digitonin