Unlocking the eukaryotic membrane protein structural proteome.

Most of the 231 unique membrane protein structures (as of 3/2010) are of bacterial membrane proteins (MPs) expressed in bacteria, or eukaryotic MPs from natural sources. However eukaryotic membrane proteins, especially those with more than three membrane crossings rarely succumb to any suitable expression in bacterial cells. They typically require expression in eukaryotic cells that can provide appropriate endoplasmic reticulum, chaperones, targeting and post-translational processing. In evidence, only approximately 20 eukaryotic MP structures have resulted from heterologous expression. This is required for a general approach to target particular human or pathogen membrane proteins of importance to human health. The first of these appeared in 2005. Our review addresses the special issues that pertain to the expression of eukaryotic and human membrane proteins, and recent advances in the tool kit for crystallization and structure determination.