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Amyloids are long, thread-like protein fibrils that form when certain proteins misfold and begin to stick together in an organised fashion. Over time, these fibrils can form aggregates or clumps known as plaques. 

This abnormal accumulation with its intercellular inclusion, called amyloidosis, is the hallmark of several serious health conditions, many of which become more common with ageing. Because of this connection, amyloids developed a negative reputation. They became widely known for their role in brain disorders such as Alzheimer’s and Parkinson’s disease, where protein aggregates disrupt normal brain function and gradually damage nerve cells. 

For many years, amyloids were viewed almost exclusively as harmful structures, molecular mistakes that needed to be prevented or removed. Yet, nature has its ways of surprising humans. Over the past two decades, researchers have discovered that amyloids aren鈥檛 always harmful. In fact, many living organisms, from simple bacteria to complex life forms, use amyloids intentionally. 

These are termed 鈥渇unctional amyloids鈥� that help microbes build protective layers, allow cells to stick together, support communication between biological systems, and store hormones. Therefore, instead of being accidental clumps, amyloids function as tiny biological tools that perform important tasks in living organisms.

The review highlights the recent advances in understanding cross-alpha amyloids. The reviewers discuss their unique structural features, stepwise assembly processes, and functional roles in natural biological systems. By integrating insights from both naturally occurring and laboratory-designed proteins/peptides, the reviewers provide a comprehensive view of their remarkable versatility. 

The reviewers also demonstrate the emerging applications of cross-alpha amyloids in biomaterials and nanotechnology, as well as in energy harvesting. 

A Structural Surprise: Discovery of the Cross-Alpha Amyloids

Since the identification of the first atomic structure of amyloid, scientists have believed that all amyloids, irrespective of their sources and amino acid sequences, share a common structural arrangement. Their protein/peptide building blocks align into flat 尾-strands, which are connected side-by-side to form a 尾-sheet structure. These sheets run along the length of the fibril axis, forming the 鈥渃ross-beta鈥� pattern. This arrangement gives amyloid fibrils their remarkable strength and stability, and for many years, it was considered the defining signature of all amyloids. 

Then, in 2017, a group of researchers discovered the structure of a completely different kind of amyloid that didn鈥檛 follow the cross-beta blueprint. Instead of being built from beta sheets, this new form was made from helical protein structures and was thus termed the 鈥渃ross-alpha鈥� amyloid. These helices stack in the same orderly manner and form rigid fibrils. This was a major shift in understanding the amyloid formation. 

Scientists realised that the same type of fibrillar assemblies of protein material could be built from a completely different secondary structural framework. This discovery didn鈥檛 just add a variation to the rule; it expanded the very definition of what an amyloid can be, opening the door to new biological insights and design possibilities.

From Nature to the Lab: Expanding the Cross-Alpha Paradigm 

Cross-alpha amyloids were first identified in certain microbes, where they serve specific biological functions. But what makes this discovery even more exciting is that scientists have also been able to design artificial short peptides in the lab that can also form cross-alpha amyloids. In other words, this structure isn鈥檛 just a rare quirk of nature; it鈥檚 something that we can intentionally build. That opens the door to creative possibilities. If proteins and peptides can be programmed to assemble into stable, well-ordered amyloid fibrils, they could be used as building materials for many pathological and technological applications.  

Why Cross-Alpha Amyloids Matter?

The dual roles of cross-alpha amyloids illustrate the complexity of biological systems. Molecules once associated solely with disease are now revealing surprising constructive and innovative roles. By studying how these protein fibrils form, organise, and function, scientists are uncovering new principles of molecular design. The field, primarily focused on preventing harmful protein aggregation, is now emerging as a frontier of bio-inspired engineering.

As researchers unravel the mechanisms governing their formation and function, opportunities are arising to harness these structures for innovative technologies. What began as a structural curiosity is rapidly becoming a foundation for future scientific and technological breakthroughs – envision custom-designed protein fibrils for drug delivery, tissue engineering, or sustainable materials in the near future.

– Edited by Priyanka, Senior Manager, Communications – Office of Research and Development, 51茶馆

This blog has been adapted from the original review article, available .