Publication highlights

Researchers at the Crick and Imperial College report a method to characterise and track sugar-coated cell sensors called proteoglycans using click chemistry. Through a 'bump and hole' engineering technique, they modified a hole in an enzyme and a bump in a sugar, to alter an enzyme that glues the two together so it accepts a bumped version of the sugar. This modified sugar contains a chemical tag which means it can be traced using click chemistry, such as attaching a fluorescent molecule to 'see' the molecule by imaging, or a molecule acting like an anchor to isolate and further study it. In the future, these molecules could be tagged and tracked in different contexts, or proteoglycan function could be altered by replacing the sugar chain with a different biological or synthetic molecule.

Members of the Chemical Glycobiology Laboratory at the Crick have developed a new method to study a type of sugar modification on proteins that is relevant for cancer. The sugar modification is initiated by an enzyme called MGAT5 that is upregulated in many types of cancer. Methods to study enzymes such as MGAT5 have been lacking, but particularly benefit from innovations in chemistry. In an international collaboration, the lab have modified the enzyme so that it can “arm” the cancer-relevant sugar with a chemical tag linked to a reporter molecule, meaning that the sugar modification and its linked proteins can be visualised, isolated and characterised.

Cell-surface and secreted proteins play critical roles in human development, growth factor signalling, and cell adhesion. Proteoglycans are an important subset of these proteins and are modified with long chains of sugar molecules called Glycosaminoglycans (GAGs) such as heparan sulphate (HS) or chondroitin sulphate (CS), but they all start with the same four sugars – only after the addition of the fifth sugar is the fate of the growing chain sealed.

While protein and DNA synthesis are template-driven, from DNA or RNA, synthesis of the proteoglycan GAG chains are not. In a collaboration between the Crick and Imperial, the researchers devised a synthesis system to allow precise control of eight of the enzymes in the biosynthesis pathway. They discovered that chrondroitin sulphate is the “default” modification, and that the enzyme responsible for priming chrondroitin sulphate synthesis modifies all sites equally. They also found that the enzyme responsible for priming heparan sulphate synthesis (EXTL3) has a positively charged patch that interacts with negatively charged amino acids near the attachment site and will only modify certain substrates. This will help to predict how mutations surrounding the glycosaminoglycan attachment sites could be implicated in diseases like cancer or developmental conditions.

Prostate cancer is the most common cancer in men and it is estimated that over 350,000 men worldwide die of prostate cancer every year. There remains an unmet clinical need to improve how clinically significant prostate cancer is diagnosed and develop new treatments for advanced disease. Aberrant glycosylation is a hallmark of cancer implicated in tumour growth, metastasis, and immune evasion. One of the key drivers of aberrant glycosylation is the dysregulated expression of glycosylation enzymes within the cancer cell. Here, the researchers demonstrate using multiple independent clinical cohorts that the glycosyltransferase enzyme GALNT7 is upregulated in prostate cancer tissue. They show GALNT7 can identify men with prostate cancer, using urine and blood samples, with improved diagnostic accuracy than serum PSA alone. They also show that GALNT7 levels remain high in progression to castrate-resistant disease, and using in vitro and in vivo models, reveal that GALNT7 promotes prostate tumour growth. Mechanistically, GALNT7 can modify O-glycosylation in prostate cancer cells and correlates with cell cycle and immune signalling pathways. The study provides a new biomarker to aid the diagnosis of clinically significant disease and cements GALNT7-mediated O-glycosylation as an important driver of prostate cancer progression.