Overcoming the challenges of membrane protein crystallography

Abstract

Membrane protein structural biology is still a largely unconquered area, given that approximately 25% of all proteins are membrane proteins and yet less than 150 unique structures are available. Membrane proteins have proven to be difficult to study owing to their partially hydrophobic surfaces, flexibility and lack of stability. The field is now taking advantage of the high-throughput revolution in structural biology and methods are emerging for effective expression, solubilisation, purification and crystallisation of membrane proteins. These technical advances will lead to a rapid increase in the rate at which membrane protein structures are solved in the near future.

Identification of Specific Lipid-binding Sites in Integral Membrane Proteins

“…The occurrence of such interactions provides further evidence to the fact that specific protein-lipid interactions indeed play a role in the functioning of membrane proteins (4,10). The significance of membrane proteins that constitute ϳ25% of genomic sequences (19) is not reflected in the number of membrane structures that are currently available in the Protein Data Bank. Yet membrane proteins represent 70% of current drug targets (60).…”

“…The installment of membrane proteintargeted structural genomics and the rapid development of high throughput structural biology techniques are expected to result in a significant increase in the number of available membrane protein structures in the near future (19). But it is doubtful that these structures will show physiologically associated lipid molecules; the crystallization procedure typically delipidates the protein, and only the strongest bound lipid molecules may withstand the purification procedure and show sufficient electron density to be resolved at the atomic level.…”

Extracellular vesicles as a platform for membrane‐associated therapeutic protein delivery

“…Moreover, the methods for reconstituting purified membrane proteins in a lipid vesicle system (e.g., small unilamellar vesicles) are technically difficult [28,29]. These fundamental issues with expressing and purifying membrane proteins have hindered both the acquisition of proper structural information and the application of such proteins for therapeutic purposes [30,31]. …”

Arabidopsis thaliana intramembrane proteases

“…PSENs were also shown to be a subunit of the c-secretase complex, whereas the SPPs seem to act independently (Erez et al 2009). The SPPL2b protein identified in human cells was found to be proteolytically active (Fluhrer 2006;Carpenter et al 2008). In the A. thaliana genome two genes encoding presenilins, one gene encoding SPP, and five genes encoding SPP-like proteins, are present.…”