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Lavania A, Carpenter WB, Oltrogge LM, Perez D, Turnšek JB, Savage DF, Moerner WE. Exploring Masses and Internal Mass Distributions of Single Carboxysomes in Free Solution Using Fluorescence and Interferometric Scattering in an Anti-Brownian Trap. J Phys Chem B 2022; 126:8747-8759. [PMID: 36282790 PMCID: PMC9639131 DOI: 10.1021/acs.jpcb.2c05939] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Carboxysomes are self-assembled bacterial microcompartments that facilitate carbon assimilation by colocalizing the enzymes of CO2 fixation within a protein shell. These microcompartments can be highly heterogeneous in their composition and filling, so measuring the mass and loading of an individual carboxysome would allow for better characterization of its assembly and function. To enable detailed and extended characterizations of single nanoparticles in solution, we recently demonstrated an improved interferometric scattering anti-Brownian electrokinetic (ISABEL) trap, which tracks the position of a single nanoparticle via its scattering of a near-infrared beam and applies feedback to counteract its Brownian motion. Importantly, the scattering signal can be related to the mass of nanoscale proteinaceous objects, whose refractive indices are well-characterized. We calibrate single-particle scattering cross-section measurements in the ISABEL trap and determine individual carboxysome masses in the 50-400 MDa range by analyzing their scattering cross sections with a core-shell model. We further investigate carboxysome loading by combining mass measurements with simultaneous fluorescence reporting from labeled internal components. This method may be extended to other biological objects, such as viruses or extracellular vesicles, and can be combined with orthogonal fluorescence reporters to achieve precise physical and chemical characterization of individual nanoscale biological objects.
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Affiliation(s)
- Abhijit
A. Lavania
- Department
of Chemistry, Stanford University, Stanford, California94305, United States,Department
of Applied Physics, Stanford University, Stanford, California94305, United States
| | - William B. Carpenter
- Department
of Chemistry, Stanford University, Stanford, California94305, United States
| | - Luke M. Oltrogge
- Department
of Molecular and Cell Biology, University
of California Berkeley, Berkeley, California94720, United States
| | - Davis Perez
- Department
of Chemistry, Stanford University, Stanford, California94305, United States
| | - Julia B. Turnšek
- Department
of Molecular and Cell Biology, University
of California Berkeley, Berkeley, California94720, United States
| | - David F. Savage
- Department
of Molecular and Cell Biology, University
of California Berkeley, Berkeley, California94720, United States
| | - W. E. Moerner
- Department
of Chemistry, Stanford University, Stanford, California94305, United States,Department
of Applied Physics, Stanford University, Stanford, California94305, United States,
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Huang J, Jiang Q, Yang M, Dykes GF, Weetman SL, Xin W, He HL, Liu LN. Probing the Internal pH and Permeability of a Carboxysome Shell. Biomacromolecules 2022; 23:4339-4348. [PMID: 36054822 PMCID: PMC9554877 DOI: 10.1021/acs.biomac.2c00781] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
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The carboxysome is a protein-based nanoscale organelle
in cyanobacteria
and many proteobacteria, which encapsulates the key CO2-fixing enzymes ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco)
and carbonic anhydrase (CA) within a polyhedral protein shell. The
intrinsic self-assembly and architectural features of carboxysomes
and the semipermeability of the protein shell provide the foundation
for the accumulation of CO2 within carboxysomes and enhanced
carboxylation. Here, we develop an approach to determine the interior
pH conditions and inorganic carbon accumulation within an α-carboxysome
shell derived from a chemoautotrophic proteobacterium Halothiobacillus neapolitanus and evaluate the shell
permeability. By incorporating a pH reporter, pHluorin2, within empty
α-carboxysome shells produced in Escherichia
coli, we probe the interior pH of the protein shells
with and without CA. Our in vivo and in vitro results demonstrate a lower interior pH of α-carboxysome shells
than the cytoplasmic pH and buffer pH, as well as the modulation of
the interior pH in response to changes in external environments, indicating
the shell permeability to bicarbonate ions and protons. We further
determine the saturated HCO3– concentration
of 15 mM within α-carboxysome shells and show the CA-mediated
increase in the interior CO2 level. Uncovering the interior
physiochemical microenvironment of carboxysomes is crucial for understanding
the mechanisms underlying carboxysomal shell permeability and enhancement
of Rubisco carboxylation within carboxysomes. Such fundamental knowledge
may inform reprogramming carboxysomes to improve metabolism and recruit
foreign enzymes for enhanced catalytical performance.
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Affiliation(s)
- Jiafeng Huang
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Crown Street, Liverpool L69 7ZB, United Kingdom.,School of Life Sciences, Central South University, Changsha 410017, China
| | - Qiuyao Jiang
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Crown Street, Liverpool L69 7ZB, United Kingdom.,Department of Central Laboratory, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan 250021, China
| | - Mengru Yang
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Crown Street, Liverpool L69 7ZB, United Kingdom
| | - Gregory F Dykes
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Crown Street, Liverpool L69 7ZB, United Kingdom
| | - Samantha L Weetman
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Crown Street, Liverpool L69 7ZB, United Kingdom
| | - Wei Xin
- Department of Central Laboratory, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan 250021, China.,Medical Science and Technology Innovation Center, Shandong First Medical University & Shandong Academy of Medical Sciences, Jinan 271000, China
| | - Hai-Lun He
- School of Life Sciences, Central South University, Changsha 410017, China
| | - Lu-Ning Liu
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Crown Street, Liverpool L69 7ZB, United Kingdom.,College of Marine Life Sciences, and Frontiers Science Center for Deep Ocean Multispheres and Earth System, Ocean University of China, Qingdao 266003, China
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Abstract
Despite the importance of microcompartments in prokaryotic biology and bioengineering, structural heterogeneity has prevented a complete understanding of their architecture, ultrastructure, and spatial organization. Here, we employ cryo-electron tomography to image α-carboxysomes, a pseudo-icosahedral microcompartment responsible for carbon fixation. We have solved a high-resolution subtomogram average of the Rubisco cargo inside the carboxysome, and determined the arrangement of the enzyme. We find that the H. neapolitanus Rubisco polymerizes in vivo, mediated by the small Rubisco subunit. These fibrils can further pack to form a lattice with six-fold pseudo-symmetry. This arrangement preserves freedom of motion and accessibility around the Rubisco active site and the binding sites for two other carboxysome proteins, CsoSCA (a carbonic anhydrase) and the disordered CsoS2, even at Rubisco concentrations exceeding 800 μM. This characterization of Rubisco cargo inside the α-carboxysome provides insight into the balance between order and disorder in microcompartment organization.
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