Exploring molecular landscapes inside cells with in situ cryo-electron tomography

Cells accomplish the biochemical reactions of life by concentrating their proteins into a variety of subcellular compartments called organelles. Engel’s group explores the relationship between the form of the organelle and the function of its resident macromolecules. How does organelle architecture direct molecular function, and reciprocally, how do macromolecules sculpt and shape organelles? To investigate these questions, they use focused ion beam (FIB) milling of frozen cells followed by cryo-electron tomography to image macromolecules within their native cellular environment. Through a combination of nanometer-precision localization and high-resolution structural analysis, Engel aims to chart the molecular landscapes of organelles. Thanks to its superb cryo-EM contrast and textbook organelle architecture, the unicellular green alga Chlamydomonas is an ideal specimen for this approach. Engel’s group has taken a holistic approach to survey the whole integrated “planimal”, with in situ molecular studies of the nuclear envelope, ER, Golgi, basal body apparatus (centrioles), and chloroplast. In this talk, Engel will provide an overview of some of these studies, touching on proteasome-rich degradation centers, the nuclear pore complex, COPI coats, and the molecular organization of chloroplast’s thylakoid membranes and pyrenoid.