Structural and Dynamic Basis of Polysaccharide Production at the Cell Surface
The Stansfeld GroupLink opens in a new window, in the School of Life Sciences and Department of Chemistry, University of Warwick, have published two papers in the journal Nature on the production of polysaccharides around cells.
In the first paper, in collaboration with Jochen Zimmer, University of Virginia (US), the process of how hyaluronic acid is stitched together and secreted by enzyme called hyaluronan synthase (HAS) was determined. Hyaluronic acid is an essential polysaccharide, with broad medical applications. Our bodies naturally produce hyaluronic acid to hydrate cells, heal wounds, and lubricate joints. The molecule also helps form new tissues and plays a role in cancer metastasis. Furthermore, as many cosmetic enthusiasts will be aware, hyaluronic acid is a superfood for skin, and is found in moisturisers, and a variety of other cosmetics as a molecule to increase the suppleness and smoothness of the skin.
In the second study, the process by which Gram-negative bacteria create their liposaccharide outer coat was uncovered by capturing the structure and interactions of the WaaL ligase, in collaboration with Filippo Mancia, at Columbia University (US) (https://www.mancialab.com), and Stephen Trent, at the University of Georgia (US) (https://mib.uga.edu/directory/people/m-stephen-trent), and several other colleagues, including David Roper in Life Sciences at Warwick who was also a recent visiting Schaeffer research fellow at Columbia in the Mancia group (https://warwick.ac.uk/fac/sci/lifesci/people/droper/). Here they uncover how the outer O-antigen sugars are added to the Lipid A core of lipopolysaccharide. These polysaccharides are the foremost barrier on the outside of a bacterial cell and therefore a major hurdle for novel antimicrobials to overcome to permit access to the bacterial cell to have their antibacterial effects.
Both publications have applied cryo-electron microscopy (EM) simulations, in combination with protein antibodies to increase the overall size of the small membrane protein structures. In WaaL’s case fragments of antibodies (FABs) were developed by the lab of Anthony Kossiakoff (https://kosslab.uchicago.eduLink opens in a new window), while for HAS, the Jan Steyaert lab (https://steyaertlab.sites.vib.be/Link opens in a new window) engineered HAS-selective nanobodies from llamas. The addition of the antibodies makes the images derived from the cryo-EM method easier to piece together and therefore increased the likelihood of capturing a high-quality structure.
For both projects, the Stansfeld group have used a computational approach called molecular dynamics (MD) simulations to uncover how the substrate polysaccharides and lipids bind and interact with the two enzymes. This information provides a means to understand how the enzymes work and therefore how the processeses may either be optimised or inhibited.
For HAS, they show how the enzyme alternatively adds two sugars (N-acetylglucosamine and glucuronic acid) to the growing hyaluronan polysaccharide chain while simultaneously pushing the chain out of the cell. For WaaL, they show how the O-antigen is delivered to the active site by a lipid-linked carrier and then is attached to the Lipid A core oligosaccharide.
The HAS work could allow scientists to tweak HAS and potentially develop new hyaluronic acid-based biomaterials. Engineered hyaluronic acids could aid wound healing, dermal fillers for use in cosmetic or reconstructive surgeries, and perhaps even anti-cancer treatments. While the WaaL study may enable the development of much needed new antibiotics to inhibit the production of the bacterial surface.
The next step is to understand how both enzymes produce polysaccharides of different type and size, and how these processes differ in distinct organisms. These discoveries aim to provide a basis to develop novel therapeutics.
Finn P. Maloney, Jeremi Kuklewicz, Robin A. Corey et al.
“Structure, substrate-recognition, and initiation of hyaluronan synthase.”
https://www.nature.com/articles/s41586-022-04534-2 Link opens in a new window
Khuram Ashraf, Rie Nygaard, Owen N. Vickery et al.
“Structural basis of Lipopolysaccharide Maturation by the WaaL O-Antigen Ligase.”
https://www.nature.com/articles/s41586-022-04555-xLink opens in a new window