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.

Researchers at the Crick and King's College London have used phototherapy to inhibit a protein in E. Coli bacteria that makes them resistant to antibiotics. They designed a new chemical tool, Ru1, composed of a light-activated ruthenium metal complex attached to an organic ligand that binds to NDM-1, an enzyme in drug-resistant bacteria that breaks down common beta-lactam antibiotics like penicillin. When exposed to blue light, the metal complex produces reactive oxygen species that cause damage to NDM-1, preventing it from binding and destroying an antibiotic. They showed that Ru1 can boost the activity of meropenem antibiotic against E. Coli by 53 times, without showing toxicity to human cells.

Chemical reactions are initiated by an energy source that can be provided by heat, electric current or light, and are generally governed by the rules of thermodynamics. Mechanical forces are an alternative means of activating chemical reactions, often steering reaction pathways that result in products different from those obtained under thermodynamic control. In this work, researchers from the Crick demonstrated that mechanical forces activate chemical reactions that are chemically forbidden, such as the reduction of an individual protein disulfide bond by an inorganic sulfur-oxyanion. Occurring within the core of a protein with a physiological mechanical role, the force-unlocked reactivity has a direct impact on protein elasticity.

The amount of any given protein in a cell has to be controlled to keep its levels within a range required for healthy functions, which is especially important for proteins that group together in condensates which generally contain flexible parts and can form many interactions at the same time. Aiming to discover how the cell regulates the amounts of these proteins, researchers at the Crick and King's College London's UK Dementia Research Institute investigated nuclear speckles, condensates in the nucleus, discovering a new way for cells to maintain the equilibrium of many proteins that condense together. They termed this 'interstasis': how the accumulation of various proteins in a condensate can decrease further production of the same proteins by capturing their own mRNAs (messenger molecules) into the same condensate. In this way the cell can regulate genes that are particularly dose-dependent and proteins which are involved in many diseases of ageing.

The Arp2/3 complex initiates the growth of new actin filaments from the side of pre-existing filaments to generate branched actin networks that are essential for many different cellular processes. However, it can also nucleate single linear actin filaments when activated by WISH/DIP/SPIN90 family proteins. Unexpectedly, researchers at the Crick together with collaborators at Birkbeck, found Arp2/3 can nucleate bidirectional linear actin filaments when activated by SPIN90. By determining the structure of SPIN90 bound to actin filaments, they uncovered the mechanism by which this bidirectional nucleation occurs. Their analysis demonstrates that single filament nucleation by Arp2/3 is mechanistically more like branch formation than previously appreciated.

As ALS involves disruption to RNA-binding proteins, which coordinate the movement and metabolism of genetic messages called RNAs, researchers at the Crick and UCL investigated how changes to an RNA-binding protein called SFPQ could underpin some of the disease pathology. They identified an alternative version of the SFPQ protein, which is found in a different cellular location compared to the regular SFPQ protein. The team then found that ALS-affected cells are more likely to produce and use the alternative SFPQ protein rather than the regular one, which mirrors findings in ALS patient tissues that SFPQ is often found in abnormal places in the cell. Finally, they showed that the alternative SFPQ has different behaviour and function, which may underlie hallmarks of the disease in ALS-affected cells. This work suggests that correcting levels of alternative SFPQ might alleviate some of the negative downstream consequences for RNA molecules and ultimately damage to nerve cells in ALS.

The DNA replication checkpoint is essential for maintaining genome stability. Without it, when DNA copying restarts after a stall, too many replication origins—the starting points for copying—are mistakenly activated, ultimately leading to cell death. Researchers at the Crick showed, in human cells lacking this checkpoint, that excessive DNA synthesis from surplus origins consumes the vital replication proteins PCNA and RFC, preventing normal restart of stalled copying at replication forks. Without the protection of PCNA and RFC, the ends of the forks are attacked by a protein called HLTF, causing irreversible damage. Removing HLTF helps cells survive even in the absence of the checkpoint, which has implications for how resistance to anti-checkpoint cancer therapies may arise.