Protein Chemistry by Lars Backman

Author:Lars Backman
Language: eng
Format: epub
Publisher: De Gruyter
Published: 2019-12-02T13:57:46.475000+00:00

8.5

Integral membrane proteins

It is much more challenging to determine the structure of an integral membrane protein than of a soluble protein. It must be possible to release the membrane protein from the membrane in an undamaged and stable form. As a membrane protein is partly hydrophobic and partly hydrophilic, it is difficult to keep the protein in solution. These are the first obstacles on the way to a structure. Still, there are two major reasons that motivate the study of these stubborn proteins: they constitute around 30% of the human proteome and around 50% of current drug targets.

It was not until the 1980s proper conditions had been worked out to obtain crystals of membrane proteins. Soon after, the first high-resolution structure of an integral membrane protein was published. Johann Deisenhofer, Robert Huber and Hartmut Michel were able to isolate, crystallize and determine the structure of the photosynthetic reaction center of the purple bacteria Rhodopseudomonas viridis by X-ray crystallography.

However, 10 years before a low-resolution model of bacteriorhodopsin, a light-driven hydrogen pump from the purple bacteria Halobacterium halobium was presented by Richard Henderson and Nigel Unwin. The structure, determined by electron microscopy, did not display any fine details, such as position of sidechains (Figure 8.6).

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