Single-Particle Chemical Force Microscopy to Characterize Virus Surface Chemistry

Mi, Xue; Heldt, Caryn L.

doi:10.2144/btn-2020-0085

Cited by 10 publications

(6 citation statements)

References 39 publications

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“…( A ) Inactivated SARS-CoV-2 particles were covalently immobilized on a Au-coated slide that contained a self-assembled monolayer that presented COOH and CH 3 functional groups. NHS/EDC chemistry covalently bound the virus to the COOH groups [ 16 , 17 ]. Au tips were functionalized to provide either negatively charged carboxyl (COO − ) or positively charged quaternary amine (NR 4 + ) groups.…”

Section: Figurementioning

confidence: 99%

“…We developed a single-particle method to measure the IEP of virus with an atomic force microscope (AFM). The technique, called chemical force microscopy (CFM), uses a functionalized AFM tip to measure the adhesion force of the functionalized AFM tip and the virus immobilized on a surface [ 16 , 17 ]. The adhesion is measured in different pH solutions, thus measuring a range of electrostatic interactions near the IEP.…”

mentioning

confidence: 99%

“…The AFM tips used must have a low spring constant (around 0.1 N/m), as the forces we are measuring are in the picoNewton range. We have also found that the magnitudes of the forces from the carboxylic acid probe are less than the quaternary amine [ 16 , 17 ]. This may be because the charge is permanent on the quaternary amine versus the carboxylic acid which is deprotonated at most pHs used in this work.…”

mentioning

confidence: 99%

“…The adhesion force between the charged probe and the covalently bound virus using NHS/EDC chemistry was measured in 20 mM citrate buffer between pH 4–6 or 20 mM phosphate buffer at pH 7.0 with an AFM. By measuring a range of pHs, the IEP could be determined, as described previously [ 16 , 17 ], and is shown in Figure 1 . The measured IEP for SARS-CoV-2 (USA-WA1/2020) was 5.2–5.3.…”

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Single-Particle Characterization of SARS-CoV-2 Isoelectric Point and Comparison to Variants of Interest

et al. 2021

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SARS-CoV-2, the cause of COVID-19, is a new, highly pathogenic coronavirus, which is the third coronavirus to emerge in the past 2 decades and the first to become a global pandemic. The virus has demonstrated itself to be extremely transmissible and deadly. Recent data suggest that a targeted approach is key to mitigating infectivity. Due to the proliferation of cataloged protein and nucleic acid sequences in databases, the function of the nucleic acid, and genetic encoded proteins, we make predictions by simply aligning sequences and exploring their homology. Thus, similar amino acid sequences in a protein usually confer similar biochemical function, even from distal or unrelated organisms. To understand viral transmission and adhesion, it is key to elucidate the structural, surface, and functional properties of each viral protein. This is typically first modeled in highly pathogenic species by exploring folding, hydrophobicity, and isoelectric point (IEP). Recent evidence from viral RNA sequence modeling and protein crystals have been inadequate, which prevent full understanding of the IEP and other viral properties of SARS-CoV-2. We have thus experimentally determined the IEP of SARS-CoV-2. Our findings suggest that for enveloped viruses, such as SARS-CoV-2, estimates of IEP by the amino acid sequence alone may be unreliable. We compared the experimental IEP of SARS-CoV-2 to variants of interest (VOIs) using their amino acid sequence, thus providing a qualitative comparison of the IEP of VOIs.

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Single-Particle Characterization of SARS-CoV-2 Isoelectric Point and Comparison to Variants of Interest

et al. 2021

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“…We have developed a method to measure the chemical differences between individual viral particles using an atomic force microscope . The adhesion of a chemically modified atomic force microscope tip in buffers of different pH has been used to determine the isoelectric point of three viruses. , This single-particle measurement does not require extremely pure stocks of virus when studying isoelectric points or other full population characteristics.…”

Section: Introductionmentioning

confidence: 99%

Empty and Full AAV Capsid Charge and Hydrophobicity Differences Measured with Single-Particle AFM

et al. 2023

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Adeno-associated virus (AAV) is showing promise as a therapy for diseases that contain a single-gene deletion or mutation. One major scale-up challenge is the removal of empty or non-gene of interest containing AAV capsids. Analytically, the empty capsids can be separated from full capsids using anion exchange chromatography. However, when scaled up to manufacturing, the minute changes in conductivity are difficult to consistently obtain. To better understand the differences in the empty and full AAV capsids, we have developed a single-particle atomic force microscopy (AFM) method to measure the differences in the charge and hydrophobicity of AAV capsids at the single-particle level. The atomic force microscope tip was functionalized with either a charged or a hydrophobic molecule, and the adhesion force between the functionalized atomic force microscope tip and the virus was measured. We measured a change in the charge and hydrophobicity between empty and full AAV2 and AAV8 capsids. The charge and hydrophobicity differences between AAV2 and AAV8 are related to the distribution of charge on the surface and not the total charge. We propose that the presence of nucleic acids inside the capsid causes minor but measurable changes in the capsid structure that lead to measurable surface changes in charge and hydrophobicity.

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An Update on Theoretical and Metrological Aspects of the Surface Hydrophobicity of Virus and Virus‐Like Particles

Sautrey

2024

Advanced Biology

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Viruses are biological entities embodied in protein‐based nanoparticles devoid of metabolic activity. Hence, the colloidal, interfacial, and chemical reactivity of virus particles (VPs) profoundly affects the fate of natural and artificial viruses in biotic or abiotic aqueous systems. These rely on the physical chemistry at the outer surface of VPs. In other words, whether wild or synthetic VPs and regardless of the scientific fields involved, taming viruses implies thus managing the physical chemistry at the VP external surface. The surface hydrophobicity (SH) of VPs is a critical feature that must be looked at. Still, the literature dealing with nanoscale hydrophobic domains at the proteinaceous surface of VPs underlying their global SH is like a fragmented puzzle. This article provides an overview of the topic from the perspective of modern protein biophysics for updating the classic physicochemical picture of outer VP/water interfaces hitherto accepted. Patterns of non‐polar and “false‐polar” patches, expressing variable hydrophobic degrees according to neighboring polar patches, are now drawn. The extensive discussion of reviewed data generates such fresh ideas to explore in the coming years for better modeling the SH of wild virions or engineered virus‐based nanoparticles, paving the way for new directions in fundamental virology and virus‐based chemistry.

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Single-Particle Chemical Force Microscopy to Characterize Virus Surface Chemistry

Cited by 10 publications

References 39 publications

Single-Particle Characterization of SARS-CoV-2 Isoelectric Point and Comparison to Variants of Interest

Single-Particle Characterization of SARS-CoV-2 Isoelectric Point and Comparison to Variants of Interest

Empty and Full AAV Capsid Charge and Hydrophobicity Differences Measured with Single-Particle AFM

An Update on Theoretical and Metrological Aspects of the Surface Hydrophobicity of Virus and Virus‐Like Particles

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