Unveiling the Mechanisms of Flagellin Glycosylation in Bacteria: Insights from Shewanella oneidensis

@Patrick_Viollier

Bacteria use a locomotive structure called the flagellum to move through liquid environments and spread during infections. The external part of the flagellum, known as the filament, is often decorated with glycans (sugars) from the sialic acid class. This process, called flagellin glycosylation, involves the covalent attachment of sialic acid derivatives to the flagellin protein subunits of the filament. Specialized proteins ensure that the glycans are correctly recognized and attached to specific sites on the flagellin.

In their recent study, GCIR Professor Patrick Viollier and his team explored two flagellin glycosylation systems, Maf-1 and Maf-2, in the environmental bacterium Shewanella oneidensis. They discovered that both systems use the same sialic acid derivative but attach it to different serine residues on the flagellin. Despite being evolutionarily related, Maf-1 and Maf-2 operate differently. Maf-2, which is shorter, requires an additional "helper" protein called GlfM to guide it to the flagellin. In contrast, Maf-1 has a built-in helper region attached to its tail that facilitates flagellin binding.

These findings shed light on the evolution of flagellin modification systems utilizing sialic acids. Sialic acid is not unique to human cells; it is also present in bacteria and archaea. Understanding how these proteins are selectively modified with sialic acids can provide valuable insights into similar processes in humans. This knowledge may also lead to advancements in biotechnology, particularly in reprogramming protein glycosylation systems for medical applications.

Full article: https://doi.org/10.1016/j.cub.2024.05.058

Exploring Bacterial Flagellin Glycosylation: Why is it important?

The research team focused on sialic acids, a type of sugar found on the surfaces of many bacteria. These sugars play an important role in how the human immune system recognizes and responds to bacterial infections. Sialic acids are present in different parts of bacteria, such as the capsule (K-antigen), the outer membrane (O-antigen), and the flagellin (H-antigen), which helps bacteria move.

Flagellin, in particular, can trigger a strong immune response and is being studied for its potential in vaccines and treatments. When flagellin is modified with sialic acid, it could help create better vaccines by boosting the immune system. Understanding how sialic acids attach to flagellin is crucial for developing these new medical tools.

In their study, the team examined how two systems, Maf-1 and Maf-2, add sialic acids to flagellin in a bacterium called Shewanella oneidensis. They discovered that although Maf-1 and Maf-2 use the same type of sialic acid, they attach it to different spots on the flagellin protein. Additionally, Maf-2 needs a helper protein called GlfM to function, while Maf-1 has a built-in helper.

By learning how these systems work, the team can start to engineer flagellin-derived vaccine carriers glycosylated with sialic acids. This is a significant step toward creating new vaccines and treatments that enhance the immune system's ability to fight infections.

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