Superresolution microscopy of the β-carboxysome reveals a homogeneous matrix

• Published in: Molecular biology of the cell Vol. 28; no. 20; pp. 2734 - 2745
• Main Authors: Niederhuber, Matthew J, Lambert, Talley J, Yapp, Clarence, Silver, Pamela A, Polka, Jessica K
• Format: Journal Article
• Language: English
• Published: United States The American Society for Cell Biology 01-10-2017
• Subjects: Bacterial Proteins - metabolism; Carbon Cycle; Carbon Dioxide - metabolism; Cyanobacteria - enzymology; Cyanobacteria - metabolism; Microscopy - methods; Organelles - metabolism; Protein Isoforms; Protein Transport; Ribulose-Bisphosphate Carboxylase - metabolism; Synechococcus - enzymology; Synechococcus - metabolism
• ISSN: 1059-1524; 1939-4586
• DOI: 10.1091/mbc.E17-01-0069

Carbon fixation in cyanobacteria makes a major contribution to the global carbon cycle. The cyanobacterial carboxysome is a proteinaceous microcompartment that protects and concentrates the carbon-fixing enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) in a paracrystalline lattice, making it possible for these organisms to fix CO
from the atmosphere. The protein responsible for the organization of this lattice in beta-type carboxysomes of the freshwater cyanobacterium
, CcmM, occurs in two isoforms thought to localize differentially within the carboxysome matrix. Here we use wide-field time-lapse and three-dimensional structured illumination microscopy (3D-SIM) to study the recruitment and localization of these two isoforms. We demonstrate that this superresolution technique is capable of distinguishing the localizations of the outer protein shell of the carboxysome and its internal cargo. We develop an automated analysis pipeline to analyze and quantify 3D-SIM images and generate a population-level description of the carboxysome shell protein, RuBisCO, and CcmM isoform localization. We find that both CcmM isoforms have similar spatial and temporal localization, prompting a revised model of the internal arrangement of the β-carboxysome.