A team of scientists from the Institute of Biotechnology at Vilnius University Life Sciences Centre (VU GMC) has made a significant contribution to the understanding of bacterial defence mechanisms. Led by PhD researchers Dr. Dalia Smalakytė, Audronė Rukšėnaitė, Giedrius Sasnauskas, Dr. Giedrė Tamulaitienė, and Dr. Gintautas Tamulaitis, the group has uncovered the structure and function of the CRISPR-Cas “protein scissors” found in bacteria. Their findings have been published in the prestigious journal Molecular Cell under the title “Filament Formation Activates Protease and Ring Nuclease Activities of CRISPR Lon-SAVED.
CRISPR-Cas: Nature’s Genome Editor
CRISPR-Cas systems are a bacterial immune mechanism designed to fend off viral attacks. These systems come in several variations, each with different compositions and modes of action. Among the best-known are the Cas9 and Cas12 proteins, dubbed DNA “scissors” for their ability to make precise cuts in the genome. This ability has been revolutionary for genome editing, enabling scientists to repair genetic mutations that cause diseases.
The VU GMC team, under the guidance of Dr. Tamulaitis, is focusing on a lesser-known CRISPR-Cas system: CRISPR-Cas10. This system serves as a bacterial sensor, detecting viral infections and sending molecular “messages” through the production of unique signalling molecules called cyclic oligoadenylates. These molecules activate various effector proteins that enhance the bacterium’s defences.
Unlocking the Complexity of CRISPR-Cas10
Recent computational studies predicted that CRISPR-Cas10-associated effectors might exhibit diverse enzymatic activities, allowing bacteria to defend themselves against viral threats in multiple ways. In their new research, Dr. Gintautas Tamulaitis and his team have deciphered the function of the CRISPR-Cas10-associated effector complex, CalpL-CalpT-CalpS.
“We’ve been able to investigate how this complex operates and how it’s regulated,” explains Dr. Tamulaitis. “This work opens the door to a deeper understanding of the intricate bacterial defence systems.”
The CalpL-CalpT-CalpS effector is composed of three key proteins: CalpL, a “protein scissors” that recognises viral signals; CalpS, which regulates gene expression; and CalpT, an inhibitor of CalpS. Using advanced biochemical, biophysical, and cryo-electron microscopy techniques, the scientists at VU GMC demonstrated that upon detecting viral infection, CalpL forms a polymeric filament to which the CalpT-CalpS complex binds. This filament positions the scissors to sever CalpT, releasing CalpS to regulate gene expression, which ultimately protects the bacterium from viral infection.
A Time-Controlled Response
Lead author Dr. Dalia Smalakytė highlights an important discovery: the CRISPR-Cas “protein scissors” are equipped with a time-sensitive mechanism. This internal “timer” activates as soon as the signalling molecules bind to the filament, ensuring that the bacterial defence system responds in a timely and controlled manner. This mechanism sets the CRISPR-Cas10 system apart from other bacterial defence proteins.
Implications for Future Research
This groundbreaking study not only illustrates the complexity of bacterial immune systems but also provides a foundation for future practical applications. The regulated CRISPR-Cas “protein scissors” may be harnessed as molecular indicators of infection, potentially advancing the development of new antimicrobial strategies.
“Molecular Cell is one of the leading journals in the field of molecular biology, and publishing our research here underscores the significance of our findings,” says Dr. Tamulaitis.
Funding and Support
This research was funded by the Lithuanian Research Council (LMTLT) under contract No S-MIP-22-9, with Dr. Gintautas Tamulaitis as the principal investigator.
The discovery marks an exciting leap forward in the study of CRISPR systems, offering new insights into how bacteria protect themselves from viral threats and laying the groundwork for future innovations in molecular biology.
