RETRACTED ARTICLE: Glyoxal modification mediates conformational alterations in silk fibroin: Induction of fibrillation w
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Ó Indian Academy of Sciences (0123456789().,-volV) (0123456789().,-volV)
Glyoxal modification mediates conformational alterations in silk fibroin: Induction of fibrillation with amyloidal features SAURADIPTA BANERJEE Department of Biophysics, Molecular Biology and Bioinformatics, University of Calcutta, Kolkata 700 009, India (Email, [email protected]) MS received 20 February 2019; accepted 13 January 2020 Silkworm silk protein fibroin is widely exploited to develop novel silk-based biomaterials due to its stable b-sheet structure, providing high crystallinity and tensile strength. The polymorphic behaviour of silk fibroin provides a window to modulate its structural transitions during self-assembly for different functional outcomes. Most studies are therefore mainly focused on formation of well-developed b-sheet structure and self-assembly of silk fibroin which are regulated by many parameters. Glyoxal, a highly reactive a-oxoaldehyde, reacts with different proteins to form advanced glycation end products (AGEs) following Maillard-like reaction. Considering the significance of protein modification by glyoxal-derived AGEs, in the present study the effect of glyoxal (250, 500 and 1000 lM) on the structure of silk fibroin has been investigated. CD and fluorescence studies reveal that higher concentrations of the a-oxoaldehyde induce considerable alterations of secondary and tertiary structure of the protein leading to aggregation following incubation with for 3 weeks. The aggregates exhibit fibrillar morphology with amyloidal nature as evident from SEM, FTIR and XRD experiments. The findings highlight that glycationinduced modification can be a possible approach for modulating the conformation of the silk protein which may be relevant in connection to clinical, biomedical or synthetic biology based applications. Keywords.
Advanced glycation end product; amyloid aggregation; glyoxal; silk fibroin
1. Introduction Bombyx mori silk is composed of fibroin protein coated with sericin protein. Sericins are a group of adhesive glycoproteins that account for 25–30% of the total silkworm cocoon by weight, expressed in the middle silk gland of the silkworm. Silk fibroin, on the other hand, is a hydrophobic structural protein consisting of heavy chain of *390 kDa and light chains of *26 kDa linked by disulphide bond. It is a block copolymer rich in hydrophobic b-sheet-forming blocks linked by small hydrophilic linker segments or spacers. The crystalline regions are primarily composed of glycine-X repeats, where X is alanine, serine, threonine or valine. Within these domains lie subdomains that are rich in glycine, alanine, serine and tyrosine. The result is a hydrophobic protein that self assembles to form strong and resilient materials. The dominance of the b-sheet-forming regimes within
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the fibroin structure imparts the protein-based materials high mechanical strength and toughness. Due to its stable b-sheet structure, silk fibroin has high crystallinity as well as high molecular orientation, thereby provid
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