Blue Cone Receptor Protein

Color vision in humans and other mammals uses three receptor pigments embedded in the membranes of cone cells: one each for blue, red and green light. Each of the proteins is linked to a vitamin A derivative, retinal. Each protein-retinal combination has different light-absorbing properties. The protein crosses back and forth across the membrane and has seven transmembrane segments, marked in the sequence below. Comparison of the sequences of the blue, red and green receptors suggests that they are all derived by duplication and modification of a common ancestral molecule that is in turn related to the rhodopsin of the rod cells. Mutations in these proteins have been associated with various kinds of color-blindness.

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Blue cone receptor protein

( )=extracellular domain
[ ]=transmembrane domain
{ }=cytoplasmic domain

Link to the Music: Blue Cone Receptor Protein

Notes on the music.

This piece was scored for a small group of string, wind and percussion instruments. The full 350-amino acid sequence is played through twice -- once with strings, flute and oboe, and the second time as a string trio, with other instruments playing to indicate the extracellular, transmembrane, and cytoplasmic domains of the protein. In both sections the instruments playing the full sequence play the pitches represented amino acids of low, medium and high solubility. The solo cello sequence that begins and ends the piece also represents high-solubility residues. The periodic spacing of the transmembrane domains is heard in the chimes playing at through the first section of the pieces. The chimes are played at twice the tempo of the main protein, sequence so that in this part of the piece the transmembrane "tunes" do not align with the appropriate amino acid residues represented in the strings and winds. However, the appearance and reappearance of the chimes in this section give a sense of the spacing of the transmembrane domains. In the second playthrough of the sequence, the extracellular domains are represented by piano, the transmembrane domains by oboe and the cytoplasmic domains by bells.