First Theorized 70 Years Ago – “Rippled Beta Sheet” Created for the First Time

Rippled Beta Sheet

The rippled beta sheet is a variation of the pleated beta sheet, a well-known structural motif found in thousands of proteins. Linus Pauling and Robert Corey described the rippled beta sheet in 1953, but it remained a largely theoretical structure for decades. Scientists have now created rippled sheets in the laboratory and characterized the structure using x-ray crystallography. Credit: J. Raskatov

University of California, Santa Cruz, scientists report the creation of three crystal structures of periodic rippled beta sheets, a novel protein structure.

A peculiar protein structure known as a “rippled beta sheet,” which was initially hypothesized in 1953, has now been generated in the laboratory and thoroughly characterized using x-ray crystallography.

The new findings, which were published in the journal Chemical Science, may allow for the rational design of unique materials based on the rippled sheet architecture.

“Our study establishes the rippled beta sheet layer configuration as a motif with general features and opens the road to the structure-based design of unique molecular architectures, with potential for materials development and biomedical applications,” said Jevgenij Raskatov, associate professor of chemistry and biochemistry at the University of California, Santa Cruz and corresponding author of the paper.

Proteins exist in a wide range of shapes and sizes to fulfill their many structural and functional roles in living cells. Many protein structures have common structural motifs, such as the alpha helix.

The rippling sheet is a variant of the pleated beta sheet, a well-known structural motif present in thousands of proteins. Linus Pauling and Robert Corey described the rippled beta sheet two years after introducing the pleated beta sheet concept. While the pleated beta sheet is generally known and commonly referred to simply as the beta sheet, the rippled sheet has remained theoretical for decades.

In a previous study published in 2021, Raskatov’s team reported obtaining a rippled beta sheet structure by mixing a small peptide with equal amounts of its mirror image. The researchers used mirror-image forms of triphenylalanine, a short peptide consisting of three phenylalanine amino acids. The mirror-image peptides joined in pairs to form “dimers” with the predicted structure, but they did not form the extended, periodic rippled beta-sheet layer topography hypothesized by Pauling and Corey.

“The dimers packed together into herringbone layer structures, which raised doubt as to whether the periodic rippled beta-sheet layer configuration was viable,” Raskatov said.

In the new study, the researchers substituted other amino acids for one of the triphenylalanines to create slightly different tripeptides and their mirror images. Using these new tripeptides, they were able to create three different aggregating peptide systems that formed extended antiparallel rippled beta sheet layers, in which mirror-image peptide strands were arranged in an alternating fashion. The results of x-ray crystallography showed that the crystal structures are in excellent overall agreement with the predictions made by Pauling and Corey.

Reference: “The rippled β-sheet layer configuration—a novel supramolecular architecture based on predictions by Pauling and Corey” by Amaruka Hazari, Michael R. Sawaya, Niko Vlahakis, Timothy C. Johnstone, David Boyer, Jose Rodriguez, David Eisenberg and Jevgenij A. Raskatov, 15 July 2022, Chemical Science.
DOI: 10.1039/d2sc02531k

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