Local properties of biological complexes studied by local cryo-EM metrics

• Grant number: 20/01156-8
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Start date: March 01, 2021
• End date: February 28, 2025
• Field of knowledge: Biological Sciences - Biochemistry - Chemistry of Macromolecules
• Principal Investigator: Marin Gerard van Heel
• Grantee: Sayan Bhakta
• Host Institution: Centro Nacional de Pesquisa em Energia e Materiais (CNPEM). Campinas , SP, Brazil
• Associated research grant: 20/06062-1 - Biological complexes in action, in vitro and in silico (Exploiting Big-Data in Cryo-EM), AP.TEM

Abstract

Single-particle Cryogenic Electron Microscopy (Cryo-EM) has evolved from low-resolution "blobology", a few decades ago, to near-atomic resolution maps, allowing for de-novo structure determination of macro-molecular complexes today: a true "resolution revolution". The resolution assessment of the Cryo-EM results is performed routinely using a global Fourier Shell Correlation (FSC) measurement. However, local blurriness in the macromolecular structures can arise, directly associated with conformational heterogeneity and biological function. Such local effects cannot be covered by a global FSC metric. Although a number of proposals exist for defining local resolution of cryo-EM maps, they use different local metrics than the FSC used for the global one, leading to inconsistent resolution scales. The FSC is the standard resolution metric in cryo-EM and increasingly in X-ray tomography, X-ray crystallography, super resolution light microscopy, etc. By using the same metric and threshold function for global and local resolution assessed, all are mapped on the same resolution scale. Preliminary tests showing details of biological molecules confirm the validity of the approach. We already could highlight transmembrane helices in an enveloped virus, with and without the surrounding phospholipid bilayer. We also successfully imaged glycosylation on the exterior of large complexes, including those of viruses. Applications include the visualisation of dynamic interactions of factors with the ribosome which may inspire the development of new antibiotics. The proposed work will be a natural symbiosis between methods development and the study of complex biological systems. The development of user-friendly computational tools for the interpretation of dynamic biological structures are envisaged.