INTERRELATIONS OF BIOENERGETIC AND SENSORY FUNCTIONS OF THE RETINAL PROTEINS

Rhodopsins are intrinsic membrane retinal-containing proteins composed of 7 hydrophobic alpha-helical transmembrane columns and hydrophilic sequences of various length connecting the helices and localized at N- and C-ends of the polypeptide. The chromophore (retinal) forms a Schi ff base with a lysine residue in the middle part of the last alpha-hel ix. Absorption of a photon results in isomerization of retinal which g ives rise to a conformational change in the protein moiety. Rhodopsins can be involved in two entirely different types of activities, i.e. i on pumping and photosensing. Recent observations concerning the pumpin g and sensory mechanisms allowed both these events to be explained in terms of one and the same unitary concept, which postulates the format ion of a hydrophilic cleft in the hydrophobic part of the protein mole cule as a crucial step in energy conservation and photosensing.