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Quantifying oriented myelin in mouse and human brain

2021/05/262021/06/08

Myelin “insulates” our neurons enabling fast signal transduction in our brain; myelin levels, integrity, and neuron orientations are important determinants of brain development and disease. However, myelin imaging methods used in clinics or research are non-specific or destructive.

Using small-angle X-ray scattering tensor tomography (SAXS-TT), we exploited myelin’s ~17nm periodicity to non-invasively derive 3D myelin and neuron orientation maps in macroscopic tissue volumes (Figure). We demonstrated the method on a mouse brain (a-d), a mouse spinal cord, a human visual cortex and two human white matter specimens. We validated the readouts with 2D and 3D histology, and correlated the results with MRI contrasts.

Helping to neutralise greenhouse gases

2020/07/082020/07/09

Researchers used the Canadian Light Source (CLS) at the University of Saskatchewan to create an affordable and efficient electrocatalyst that can transform CO2 into valuable chemicals. The result could help businesses as well as the environment.

Electrocatalysts help to collect CO₂ pollution and efficiently convert it into more valuable carbon monoxide gas, which is an important product used in industrial applications. Carbon monoxide gas could also help the environment by allowing renewable fuels and chemicals to be manufactured more readily.

The end goal would be to try to neutralize the greenhouse gases that worsen climate change.

Precious metals are often used in electrocatalysts, but a team of scientists from Canada and China set out to find a less expensive alternative that would not compromise performance. In a new paper, the stability and energy efficiency of the team’s novel electrocatalyst offered promising results.

Read more on the Canadian Light Source website

Image : Schematic of an electrochemistry CO₂-to-CO reduction reaction.

Helping our immune systems bypass antibiotic resistance

2020/07/012020/07/01

Over 700,000 people die each year due to drug-resistant diseases and this figure could increase to 10 million per year by 2050, according to a 2019 report.

As the search continues for new antibiotics to treat drug-resistant infections, a group of researchers used the Canadian Light Source (CLS) at the University of Saskatchewan to address the problem from a different direction, by trying to weaken the ability of bacteria to develop resistance in the first place.

“The goal is to knock the bacterial cells down in terms of their resistance,” said Dr. Anthony Clarke, Professor and Dean of Science at Wilfrid Laurier University and adjunct professor at the University of Guelph. “We haven’t been successful over the last 30 years in finding new classes of antibiotics so, in the short term, we’re trying to weaken the cells so our own immune system can take over to fight infection.”

The target for his team’s work is peptidoglycan, which gives bacterial cell walls their rigidity. “Think of it as building a brick wall around the bacteria’s cells,” said Clarke. Since peptidoglycan can be broken down by lysozyme, an enzyme that exists in human immune systems, bacteria have developed strategies that block these enzymes by modifying their peptidoglycan, thereby “cementing the bricks in place,” and resisting our defences.

Read more on the Canadian Light Source website

Image: Dr. Clarke inspecting flasks of bacterial cultures in a student laboratory.

Cross-β Structure – a Core Building Block for Streptococcus mutans Functional Amyloids

2020/06/302020/08/24

Most amyloids¹ are misfolded proteins, having enormous variety in native structures. Pathological amyloids are implicated in diseases including Alzheimer’s disease and many others. They are characterized by long, unbranched fibrillar structure, enhanced birefringence on binding Congo red dye, and cross-β structure – β-strands running approximately perpendicular to the fibril axis, forming long β-sheets running in the direction of the axis. Fiber diffraction patterns from amyloids are marked by strong intensity at about 4.8 Å in the meridional direction (parallel to the fibril axis), corresponding to the separation of strands in a β-sheet, and in many cases broader but distinct equatorial intensity at about 10 Å. The 10 Å intensity (whose position may vary considerably) comes from the distance between stacked β-sheets. This stacking is characteristic of the many amyloids formed by small peptides, including peptide fragments of larger amyloidogenic proteins. While some authors have required the 10 Å intensity to characterize an amyloid, it is not strictly necessary, since architecturally more complex examples have been found of Congo-red-staining fibrils with cross-β structure, but without the stacked-sheet structure, and consequently without the 10 Å intensity on the equator.

Amyloids do not always stem from protein misfolding. Organisms across all kingdoms utilize functional amyloids in numerous biological processes. Bacteria are no exception. Bacterial amyloids contribute to biofilm formation and stability. Tooth decay is the most common infectious disease in the world. A major etiologic agent, Streptococcus mutans, is a quintessential biofilm dweller that produces at least three different amyloid-forming proteins, adhesins P1 and WapP, and the cell density and competence regulator Smu_63c². The naturally occurring truncation derivatives of P1 and WapA, C123 and AgA, represent the amyloidogenic moieties, and a new paradigm of Gram-positive bacterial adhesins is emerging of adhesins having dual functions in monomeric and amyloid forms. While each S. mutans protein possesses considerable β-sheet structure, the tertiary structures of each protein are quite different (Fig. 1). This study further characterized S. mutans amyloids and addressed the ongoing debate regarding the underlying structure and assembly of bacterial amyloids including speculation that they are structurally dissimilar from better-characterized amyloids.

Read more on the SSRL website

Image: Crystal or predicted 3D structures of S. mutans C123 (left), AgA (center), and Smu_63c (right).