Metastable Dimeric Intermediate Drives Native-like Spidroin Fibrillogenesis, while Dehydration Promotes Cross-β Transition
- 1Division of Materials Science, Graduate School of Science and Technology, Nara Institute of Science and Technology, 8916-5, Takayama, Ikoma, Nara 630-0192, Japa
Abstract
The exceptional mechanical properties of spider dragline silk originate from hierarchical spidroin self-assembly, yet mimicking this process to generate native-like structures remains challenging. Here, we report a metastable dimeric intermediate as an essential molecular factor for fibrillogenesis. Small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM) revealed a compact core stabilized by solvent-excluded "dry interfaces" surrounded by extended random coil regions. Within the core, a subset of the polyalanine blocks is held by side-chain packing rather than by main-chain {beta}-sheets; the majority remain exposed in the surrounding coil regions. Upon lowering the denaturant concentration, these exposed polyalanine segments pair with their counterparts at a fibril end, forming intermolecular {beta}-sheets that act as linkers and drive the stepwise end-to-end polymerization of the dimeric particles. In solution, the resulting fibrils exhibit an ordered {beta}-structure in which the polypeptide chains run parallel to the fibril axis, in contrast to amyloid-like cross-{beta}, in which the strands lie perpendicular to it; this matches key features of native silk nanofibril architecture. However, X-ray diffraction (XRD) analysis demonstrates that these native-like nanofibrils undergo an effectively irreversible transition toward amyloid-like cross-{beta} structures upon drying. Native-like fibrils are thus achievable by self-assembly, but structural control is lost during the final dehydration step. Accordingly, we propose a general principle for decoupling self-assembly from dehydration: native-like nanofibrils are formed first, then dried under conditions that restrict molecular-chain mobility (for example, mechanical constraint or immobilization on a surface), which we expect to suppress thermodynamic relaxation into cross-{beta} structures.
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BibTeX
@misc{kajimoto2026metastable,
title = {{Metastable Dimeric Intermediate Drives Native-like Spidroin Fibrillogenesis, while Dehydration Promotes Cross-β Transition}},
author = {H. Kajimoto and K. Yonezawa and K. S. Chan and K. Hayashi and Y. Okamoto and R. Aiba and Y. Nakatani and K. Kimura and M. Bessho and Y. Yamazaki and S. Toma-Fukai and T. Uchihashi and T. K. Sato and H. Kamikubo},
howpublished = {bioRxiv},
year = {2026},
month = sep,
doi = {10.64898/2026.09.09.749980},
url = {https://www.biorxiv.org/content/10.64898/2026.09.09.749980v1},
note = {CC BY-NC-ND},
}
RIS
TY - UNPB
TI - Metastable Dimeric Intermediate Drives Native-like Spidroin Fibrillogenesis, while Dehydration Promotes Cross-β Transition
AU - H. Kajimoto
AU - K. Yonezawa
AU - K. S. Chan
AU - K. Hayashi
AU - Y. Okamoto
AU - R. Aiba
AU - Y. Nakatani
AU - K. Kimura
AU - M. Bessho
AU - Y. Yamazaki
AU - S. Toma-Fukai
AU - T. Uchihashi
AU - T. K. Sato
AU - H. Kamikubo
PY - 2026
DA - 2026/09/09
PB - bioRxiv
DO - 10.64898/2026.09.09.749980
UR - https://www.biorxiv.org/content/10.64898/2026.09.09.749980v1
AB - The exceptional mechanical properties of spider dragline silk originate from hierarchical spidroin self-assembly, yet mimicking this process to generate native-like structures remains challenging. Here, we report a metastable dimeric intermediate as an essential molecular factor for fibrillogenesis. Small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM) revealed a compact core stabilized by solvent-excluded "dry interfaces" surrounded by extended random coil regions. Within the core, a subset of the polyalanine blocks is held by side-chain packing rather than by main-chain {beta}-sheets; the majority remain exposed in the surrounding coil regions. Upon lowering the denaturant concentration, these exposed polyalanine segments pair with their counterparts at a fibril end, forming intermolecular {beta}-sheets that act as linkers and drive the stepwise end-to-end polymerization of the dimeric particles. In solution, the resulting fibrils exhibit an ordered {beta}-structure in which the polypeptide chains run parallel to the fibril axis, in contrast to amyloid-like cross-{beta}, in which the strands lie perpendicular to it; this matches key features of native silk nanofibril architecture. However, X-ray diffraction (XRD) analysis demonstrates that these native-like nanofibrils undergo an effectively irreversible transition toward amyloid-like cross-{beta} structures upon drying. Native-like fibrils are thus achievable by self-assembly, but structural control is lost during the final dehydration step. Accordingly, we propose a general principle for decoupling self-assembly from dehydration: native-like nanofibrils are formed first, then dried under conditions that restrict molecular-chain mobility (for example, mechanical constraint or immobilization on a surface), which we expect to suppress thermodynamic relaxation into cross-{beta} structures.
ER -