Advances in Cryo-Electron Microscopy


Back in August this year I attended the EFMC-ISMC in Manchester, a really enjoyable conference with a plethora of great talks covering a variety of medicinal chemistry topics. In the emerging topics session there was a fantastic presentation from Dr Neil Ranson from the University of Leeds on the recent advances in the field of cryo-electron microscopy (cryo-EM) and its utility in structural biology. For me it was a new technique that I hadn’t seen much on before.

Recent technological advances with electron microscopes by using direct electron detectors for imaging molecules and using refined software packages that translate two dimensional sets of images into three dimensional models have pioneered the generation high resolution near atomic (< 4Å) protein structures. Reviewed nicely by Bai et al.

In his talk Dr Ranson highlighted the advantages and identified some limitations with the technique. One advantage that cryo-EM has over X-ray crystallography is that there is no prior need to crystallise the protein, reducing the time spent on optimisation of crystallisation conditions and soaking experiments. This also highlights the advantage that it is possible to obtain structural data on proteins that are notoriously difficult to crystallise, for example membrane proteins. Progress over the past couple years in this area has been significant with structures of the ion channel TRPV1 and the integral membrane protein gamma secretase being solved with cryo-EM. Of particular interest with the TRPV1 publication the ion channel is imbedded into a lipid nanodisc infrastructure, allowing the generation of more structurally relevant data of proteins in conditions that are analogous to their native biological environment. This methodology will be instrumental in the solution of further membrane protein structures, which could provide a similar impact to research as X-ray crystallography had with soluble proteins.

One of the major hurdles that cryo-EM faces is that small (<150kDa) proteins are not as static when bombarded by electrons as larger proteins or protein complexes are. This currently leads to poor data generation for small or flexible proteins and further technological development or technique refinement will be vital in progressing this area. As the technique is receiving a renewed interest from a variety of researchers, progress over these hurdles will hopefully in time be overcome.

In summary, the progress made with cryo-EM over the past few years has been substantial. Future data generated with this technique will certainly deliver structural insight into membrane proteins and protein complexes aiding the discovery of new chemical tools for these biologically important targets.

References

Review on cryo-EM – Bai et al. Trends in Biochemical Sciences, January 2015, Vol. 40, No. 1, p 49-57

TRPV1 publication – Gao et al. Nature, 16 June 2016, Vol 534, p 347-351

Gamma secretase publication – Bai et al. Nature, 10 September 2015, Vol 525, p 212-217

Blog written by Ryan West

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