ABSTRACT
Membrane Protein .........................................................................................34 3.9 Crystallization of Purified Membrane Transport Proteins ...........................35 3.10 Nuclear Magnetic Resonance (NMR) Approaches ......................................36 3.11 Conclusion ....................................................................................................36 Acknowledgments ..................................................................................................37 References ..............................................................................................................37
Membrane transport proteins are involved in nutrient capture, antibiotic efflux, protein secretion, toxin production, photosynthesis, oxidative phosphorylation, envi-
ronmental sensing, and other vital functions in bacteria (Figure 3.1). Already there is commercial interest in inhibiting the activities of some membrane transport proteins, optimizing the activities of others, employing them as transducers of electrical/chemical/mechanical energy for nanotechnology, and so on. However, membrane proteins are notoriously difficult to study. Owing to their extreme hydrophobicity, they are refractory to direct manipulation and can only be removed from the membrane, and their solubility maintained, in the presence of a detergent.1 In addition, transport proteins are usually only expressed at low levels and constitute less than 0.1% of total cell protein. Such difficulties help explain why fewer than 100 unique membrane protein structures have been resolved (see relevant examples in References2,3), although the structures of over 8000 unique soluble proteins (from almost 30,000 total structures, many not unique) have been solved. In fact, less than 1% of unique structures in the Protein Structures Database are membrane proteins, whereas they account for about 30% of all proteins in the cell.2,3
