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Theme 2 colloquium July: "Membrane-associated protein biogenesis in vitro, ex vivo and in situ" (Lecture)

Date
Tuesday 10 July 2018Add to my calendar
Time
from 16:00
Location
HG00.304
Speaker
Prof. Friedrich Förster (Cryo-Electron Microscopy, Utrecht University)
Description


Prof. Friedrich Förster (UU)Approximately one third of the cell’s proteome is synthesized at organelle membranes: the Endoplasmic Reticulum (ER) membrane hosts synthesis of secretory pathway proteins by cytosolic ribosomes and mitochondrial ribosomes residing at the inner mitochondrial membrane translate mitochondria-encoded genes. Ribosomes associate to membranes via protein complexes, which are responsible for various functions, including protein insertion/translocation into/across membranes, post-translational modification, folding, and coordination of product assembly. To address this broad range of functions, these membrane-associated ‘gateways’ are of transient nature. Both, the association with lipid membranes and the variable molecular composition make their structural and mechanistic characterization challenging; the low affinity of many interactions and the adverse effects of detergents limit the range of applications for methods requiring solubilization and purification in vitro. Cryo-electron tomography (ET) is uniquely suited to capture three-dimensional (3-D) snapshots of complexes in their native environment. Using membrane-associated protein biogenesis as an example we explain the methodology for structure determination of complexes in their different functional states to resolutions in the subnanometer regime. Ex vivo analysis of isolated organelle fractions allows determining structures of membrane-associated complexes in the organelle membranes using subtomogram averaging and classification approaches. The recent advent of the preparative cryo-focused ion beam (FIB) technology allows resolving complexes completely in situ by cryo-ET of unperturbed cells. It will be shown how insights from cryoelectron tomography alter our understanding of protein biogenesis at the ER and in mitochondria in health and disease.