Tag Archives: carbohydrates

Let’s talk to our cells!

We are one step closer to achieve communication with those 37.2 trillion tiny components that make up our bodies. If you have ever wondered how the human body is capable of doing impressive amounts of chemical work without us even thinking about it, now you can understand it! Our bodies are efficient in converting energy, and communication among our cells is key to the understanding of all the basic processes that govern our life.

Cells often communicate via receptors made of sugars, that are exposed outside of their membranes. Such processes are often carried out by tiny sugar molecules that interact with those in their specific target. Recently, a team of researchers from The University of British Columbia published a synthetic method for modified sugars with incredible potential. In other words, it is now possible to obtain reliable materials to applications in cellular communication, metabolism and other biochemical processes.

 

Figure 1: Structural representations of the transformation of sugars carried out by the researchers. Adapted from ACS Catalysis

 

This method was developed by using clones of genetically modified bacteria to express enzymes that are capable of modifying the sugar in accordance to the interest of the researcher. To achieve this, the scientists screened a library of 175 genes of the species E.coli that encoded variations of enzymes that can be used to catalyze selective chemical reactions in sugars for creating glycosidic bonds.

Computational representation of a hydrolase, an enzyme that breaks sugars. Adapted from Wikipedia

Enzymes are proteins that provide a path of a biochemical reaction to occur more efficiently. They are relatively easy to obtain and work with; however, they are specific to their target substrates which limit the extent in which their capabilities can be exploited. The scientists solved this issue by modifying the internal composition of the enzymes to improve the diversity of products in a process called selective mutagenesis. With the aid of this technique, the investigators obtained all variants that were tested in this experiment.

Schematic representation of bacterial transformation and cloning. Adapted from Griffiths et a (2000)

As the use of biotechnology increases, the understanding of our microscopic world becomes a major tool for scientific development. In this case, E.coli cells are essential since bacteria are inoculated with synthetic versions of genes that encode these enzymes and are then used as living machineries for protein production.

It is worth to mention that transformations of sugars were already reported. Nonetheless, previous methods rely on the use of expensive reagents as catalysts, which represent  a major cost and are not widely accessible. This new approach opens a significant area in biochemical research. As technology improves to newer and more accessible  methods, the diversification of these enzymes could develop new approaches for interaction with cell receptors that could enable us to understand what our cells have to say.

-Aron Engelhard

Journal Source:

Armstrong, Z.; Liu, F.; Chen, H.-M.; Hallam, S. J.; Withers, S. G. Systematic Screening of Synthetic Gene-Encoded Enzymes for Synthesis of Modified Glycosides. ACS Catalysis 20199 (4), 3219–3227.

 

Making Different Sugars with Enzyme (Pac-Man) In Our Body

Although eating too much sugar can lead to health complications, a normal intake of sugar has its benefits. This is because sugars take part not only in many cellular activities as an energy source but also in cell-cell communication as a communicator. In 2019, a research team led by Dr. Stephen Withers at the University of British Columbia made different sugars by using enzymes (Pac-Man-like molecules) in bacteria. This finding enables the building of many sugars that are commonly hard to find in nature.

What are sugars?

All sugars are made of hexagonal building blocks as shown in red in Figure 1. Two common building blocks are glucose and fructose. To make different sugars with only two common building blocks, we can vary the number and arrangement of the building blocks. For example, cellulose has three long threads that are arranged almost parallel to each other. In contrast, starch has one long thread that adopts a helical structure.

Now we know that different sugars can be made by varying the kinds of building blocks, the numbers of building blocks and the arrangements of building blocks. What we haven’t talked about is how the building blocks are linked. There are two issues with linking the building blocks. First, building blocks are much smaller than our cells. Getting two building blocks together is as hard as fishing a needle from the Pacific Ocean. Besides, getting two building blocks together takes time because they prefer to be alone. How can our mother nature solve these problems to keep us alive?

Figure 1. Sugars are built differently. Some sugars are longer and more complex than others. Source: riasparklebiochemistry

Here comes the rescue…Pac-Man in the cells!

The illustrations of enzymes are like Pac-Man. However, different from Pac-Man that eats any “food” in different shapes, enzymes recognize different substrates and those substrates only! Because of this substrate-enzyme specificity, linking two building blocks together is much easier. As shown in Figure 2, the enzyme will attract two specific building blocks, making them closer to each other and eventually join.

Figure 2. Different enzymes recognize different substrates. Source: Wikipedia

Besides, enzymes can speed up the “hugging” process between the substrates (building blocks), making the formation of a long sugar favorable.

Figure 3. Enzymes speed up reactions. Source: pinimg.com

Manipulation of enzymes to build different sugars for cell-cell communication

Knowing that enzymes have many advantages, Dr. Wither and his team looked for enzymes that speed up the linkage of sugar building blocks in E. Coli, bacteria that live inside our digestive tracts. They chose eight enzymes out of the 175 sugar-specific enzymes in E. Coli. These eight enzymes were the most specific to the sugar building blocks they were interested in. However, after further investigation, the researchers found that the enzymes helped speed up the breakage of the linkage(s) between sugar building blocks instead of the formation of the linkage(s).

Figure 4. Some enzymes speed up the breakage of linkages while others speed up the formation of linkages.
Source: Canstock.com

To solve this problem, the researchers reverse-engineered these enzymes from speeding up breakage to speeding up linkage by changing parts of the enzymes. Now different sugars can be made! As mentioned above, cell-cell communication relies on sugars. This is because two cells adhere via the interaction between extracellular sugars and specific cell-surface receptors. Once these cells adhered to each other, they can talk to each other about their internal cellular condition/environment and trigger a corresponding response. This has great implications in triggering an immune response to a viral attack. By engineering more sugars on the surface of the cells, cells in our immune system can more quickly talk to each other and fight off infection.

 

Journal Source:

Armstrong, Z.; Liu, F.; Chen, H.-M.; Hallam, S. J.; Withers, S. G. Systematic Screening of Synthetic Gene-Encoded Enzymes for Synthesis of Modified Glycosides. ACS Catalysis 20199 (4), 3219–3227.

-Pricia Ouyang