ABSTRACT
Membrane proteins are of critical importance for a wide variety of biological processes. They constitute ion channels, transport proteins, receptors for hormones, light, and odorants, just to mention a few examples. Over half of prescription drugs act on G protein-coupled receptors.1 In the completely sequenced genomes, the proportion of genes coding for membrane proteins is estimated to be about 25%.2-4
In spite of the biological importance of membrane proteins, there are only a few proteins for which the three-dimensional structures have been solved experimentally due to difficulties in crystallizing these proteins. Currently, only about 1 to 2% of all structures in the PDB5 are membrane proteins.6 Thus, there is a large gap to bridge. Bioinformatics can be of great value when it comes to identifying membrane-
spanning proteins from the amino acid sequence alone and predicting their topology, that is, delineating the transmembrane segments and the orientation of the protein in the membrane.
