Hartmut MICHEL

Nobel Laureate in Chemistry,
Max Planck Institute of Biophysics, Frankfurt am Main, Germany

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Title: Membrane Proteins - Importance, Functions, Mechanism

All living cells are surrounded by membranes. In addition, cells of higher organisms are compartmentalized by internal membranes. Biological membranes consist of lipids and membrane proteins. The lipids have a more passive role and lead to the electric insulator properties of biological membranes. As a consequence electric voltages can be generated and maintained across membranes. The proteins inserted into membranes are more active players. Functionally they can be classified as follows:

(i) Transporters and channels allow the passage or transport selected substrates across the membranes.
(ii) Many of them act as sensors and signal receptors and transduce the signals across the membranes.
(iii) Others are involved in biological electron transfer, e.g. in cellular respiration or photosynthesis.
(iv) Some act as enzymes, in particular for hydrophobic substrates.

Membrane proteins constitute about 30 % of all proteins, but more than 50 % of all drugs act by blocking or activating membrane proteins. Therefore there is a big interest in medicine and the pharmaceutical industry to understand membrane proteins. Handling of membrane proteins is difficult, because there surface is partly hydrophobic and partly hydrophilic. Nevertheless a few of them could be crystallized and their structures could be determined by X-ray crystallography. Examples of membrane proteins involved in transport and in electron transfer will be presented and their mechanisms of action will be discussed.