Grafting a short chameleon sequence from αB crystallin into a β‐sheet scaffold protein

Abstract

Many protein and peptide sequences are self‐assembled into β‐sheet‐rich fibrous structures called amyloids. Their atomic details provide insights into fundamental knowledge related to amyloid diseases. To study the detailed structure of the amyloid, we have developed a model system that mimics the self‐assembling process of the amyloid within a water‐soluble protein, termed peptide self‐assembly mimic (PSAM). PSAM enables capturing of a peptide sequence within a water‐soluble protein, thus making structural and energetics‐related studies possible. In this work, we extend our PSAM approach to a naturally occurring chameleon sequence from αB crystallin. We chose “Val–Leu–Gly–Asp–Val (VLGDV)”, a five amino‐acid sequence, which forms a β‐turn in the native structure and a β‐barrel in the amyloid oligomer cylindrin, as a grafting sequence to the PSAM scaffold. The crystal structure revealed that the sequence grafting induced β‐sheet bending at the grafted site. We further investigated the role of the central glycine residue and found that its role in the β‐sheet bending is dependent on the neighboring residues. The ability of PSAM to observe the structural alterations induced by the grafted sequence provides an opportunity to evaluate the structural impact of a sequence from the peptide self‐assembly.

Structural analysis of the β‐sheet edge of peptide self‐assembly using a model protein

“…28 PSAM-edge was expressed as a soluble form in Escherichia coli the wild-type (OspA-sm1; 2.8 M). 19,22 The results indicate that PSAM-edge shows cooperative unfolding even though it lacks a C-terminal capping domain.…”

“…Urea concentrations were determined using a refractometer NAR-3 T (ATAGO Co. Ltd., Japan). The data were fitted to a two-state unfolding model as described previously 19,22 by an IgorPro software. Protein samples with urea (7.95 M) and without (0 M) were mixed to obtain various urea concentration samples.…”

“…We termed the resulting model system a peptide self-assembly mimic (PSAM). [16][17][18][19][20][21] The β-meander structure of SLB mimics peptide self-assembly. Each SLB is capped by two-terminal domains and these capping domains prevent the aggregation of SLB via sticky β-sheet edges.…”

Residue-Specific Binding Mechanisms of Thioflavin T to a Surface of Flat β-Sheets within a Peptide Self-Assembly Mimic

“…We developed a model system for mimicking protein/peptide self-assembly [peptide self-assembly mimic (PSAM)] − based on a Borrelia protein known as outer surface protein A (OspA; UniProtKB P0CL66). OspA has a unique structural feature in which two terminal domains are connected by a single-layer β-sheet (SLB), which consists of a flat β-meander structure that can mimic a β-strand assembly (Figure b).…”