膜蛋白的结构与功能(三).ppt

Bacteriorhodopsin
Introduction to bacteriorhodopsin
Archaebacteria Halobacteria Salinarium are the source of bacteriorhodopsin
They are halophilic bacteria (found in very salty water . Great Salt Lake)
Bacteriorhodopsin
The purple membrane patches are areas on the membrane where BR is concentrated
BR absorbs light at 570 nm (visible green light)
Red and Blue light is reflected, giving membrane its purple colour
Bacteriorhodopsin
The purple membrane was built by replicating in space a hexagonal unit cell using periodic boundary conditions. The unit cell contains 3 monomeric bR molecules, 28 lipid molecules, and 8410 water molecules, giving a total number of 23783 atoms. This structure is replicated in all directions of space, following a hexagonal symmetry, to construct a multilammelar PM model.
Bacteriorhodopsin
The function of bacteriorhodopsin
—bacteriorhodopsin functions as a proton pump
—Bacteriorhodopsin uses light energy to pump H+ to the exterior of the cell, thus generating a H+ electrochemical gradient, or proton-motive force
—Photons react with a bound retinal group causing conformational change in bacteriorhodopsin
—The cells use this proton-motive force to synthesise ATP and to perform other vital functions requiring energy expenditure
Bacteriorhodopsin
Bacteriorhodopsin takes energy from photons
This energy is converted and creates a proton gradient by pumping protons outside the cell
Protons are allowed back into the cell by an ATP synthase
In a nutshell: Photons are used to power the cell
Bacteriorhodopsin
Extracellular matrix
Cytosol
OK
H
H
-D85 deprotonated
-PRS reprotonated
-back to square 1 until
another proton isomerizes
the All-trans retinal
PRS
H
H+
Early Electron Microscopy Studies of Bacteriorhodopsin
Bacteriorhodopsin naturally forms 2-dimensional crystals.
Lipid is 25 % of purple membrane & bR is the other 75 %.
First membrane protein structure: Henderson & Unwin, Nature 257, 28-32 (1975).
Electron micro