A sharper image for proteins

Date:
April 28, 2022
Source:
Arizona State University
Summary:
Scientists describe a new technique that promises to revolutionize
the imaging of proteins and other vital biomolecules, allowing
these tiny entities to be visualized with unprecedented clarity
and by simpler means than existing methods.



FULL STORY ========================================================================== Proteins may be the most important and varied biomolecules within living systems. These strings of amino acids, assuming complex 3-dimensional
forms, are essential for the growth and maintenance of tissue, the
initiation of thousands of biochemical reactions, and the protection of
the body from pathogens through the immune system. They play a central
role in health and disease and are primary targets for pharmaceutical
drugs.


==========================================================================
To fully understand proteins and their myriad functions, researchers
have developed sophisticated means to see and study them through
advanced microscopy, improving light detection, imaging software, and
the integration of advanced hardware systems.

In a new study, corresponding author Shaopeng Wang and his colleagues
at Arizona State University describe a new technique that promises to revolutionize the imaging of proteins and other vital biomolecules,
allowing these tiny entities to be visualized with unprecedented clarity
and by simpler means than existing methods.

"The method we report in this study uses normal cover glass instead of
gold coated cover glass, which has two advantages over our previously
reported label-free single-protein imaging method, Wang says. It is
compatible with fluorescence imaging for in-situ cross validation, and it reduces the light- induced heating effect that could harm the biological samples. Pengfei Zhang, an outstanding postdoctoral researcher in my
group, is the technical lead of this project." Wang has a joint faculty position in the Biodesign Center for Bioelectronics and Biosensors and
School of Biological and Health Systems Engineering. The group's research findings appear in the current issue of the journal Nature Communications.

The new method, known as evanescent scattering microscopy (ESM), is based
on an optical property first recognized in antiquity, known as total
internal reflection. This occurs when light passes from a high-refractive medium, (like glass) into a low-refractive medium (like water).



==========================================================================
When the angle of incident light is moved away from the perpendicular
(relative to the surface), it eventually reaches the "critical angle," resulting in all the incident light being reflected, rather than
passing through the second medium. (To properly illuminate biological
samples, laser light is used.) Total internal reflection produces an evanescent field, which can excite cells or molecules like proteins at
the glass-water interface, when such molecules are affixed to a cover
glass, allowing researchers to visualize them in startling detail.

Previous methods commonly label the biomolecules of interest with
fluorescent tags known as fluorophores, to better image them. This process
can interfere with the subtle interactions being observed and requires cumbersome sample preparation. The ESM technique is a label-free imaging
method requiring no fluorescent dye or gold coating for sample slides.

Instead, the method exploits subtle irregularities in the surface of
the cover glass to produce images of razor-sharp contrast. This is
achieved by imaging the interference of evanescent light scattered by
the single-molecule samples and the rough texture of the cover glass.

The use of evanescent wave scattering allows samples, including proteins,
to be probed at extremely shallow depth, typically <100 microns. This
allows ESM to create an optical slice, with dimensions comparable to a
thin electron microscopy section.

The new study describes the use of ESM to detect four model
proteins:bovine serum albumin (BSA), mouse immunoglobulin G (IgG),
human immunoglobulin A (IgA), human immunoglobulin M (IgM).

Protein-protein interactions, including the rapid binding and
dissociation of individual proteins were observed in a series of
experiments. Understanding such binding kinetics is essential for the
design of safer and more effective drugs. The researchers also used ESM
to keenly observe conformational changes in DNA, further demonstrating
the power and versatility of the new method.


========================================================================== Story Source: Materials provided by Arizona_State_University. Original
written by Richard Harth. Note: Content may be edited for style and
length.


========================================================================== Journal Reference:
1. Pengfei Zhang, Lei Zhou, Rui Wang, Xinyu Zhou, Jiapei Jiang,
Zijian Wan,
Shaopeng Wang. Evanescent scattering imaging of single
protein binding kinetics and DNA conformation changes. Nature
Communications, 2022; 13 (1) DOI: 10.1038/s41467-022-30046-8 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220428104010.htm

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