Nady, A. | bioRxiv Science

bioRxiv2024

An amyloidogenic fragment of the SARS CoV-2 envelope protein promotes serum amyloid A misfolding and fibrillization

SARS CoV-2 infection can affect a surprising number of organs in the body and cause symptoms such as abnormal blood coagulation, fibrinolytic disturbances, and neurodegeneration. Our study delves into the intricate pathogenic potential of a SARS-CoV-2 envelope protein peptide, shedding light on its implications for multi-organ effects and amyloid formation. Specifically, we focus on the peptide SK9 or 54SFYVYSRVK62 derived from the C-terminus of human SARS coronavirus 2 envelope protein. We demonstrate that SK9 containing peptides readily form classic amyloid structures consistent with predictions of amyloid aggregation algorithms. In vivo, overexpression of proteases such as neutrophil elastase during inflammation can potentially lead to C-terminal peptides containing SK9. We also demonstrate that SK9 can promote the fibrillization of SAA, a protein marker of acute inflammation. Our investigations reveal that the aromatic residues Phe2 and Tyr3 of SK9 play a pivotal role in its amyloidogenic function. We show that the primary sites of SK9-SAA binding lie in the amyloidogenic hotspots of SAA itself. Our results highlight two possible complications of SARS CoV-2 infection in individuals with hyper-inflammation either due to amyloids arising from SK9 containing peptides or SK9-induced AA amyloidosis.

biochemistry↗

bioRxiv2023

Structural studies of a serum amyloid A octamer that is primed to scaffold lipid nanodiscs

Serum amyloid A (SAA) is a highly conserved acute-phase protein that acts on multiple pro-inflammatory pathways during the inflammatory response and is used as a biomarker of inflammation. It has also been linked to beneficial roles in tissue repair through improved clearance of lipids and cholesterol. In patients with chronic inflammatory diseases, elevated SAA may contribute to increased severity of the underlying condition. The majority of circulating SAA is bound to high-density lipoprotein (HDL), stabilizing SAA and altering its functional properties, likely through altered accessibility of protein-protein interaction sites on SAA. While high-resolution structures for lipid-free forms of SAA have been reported, their relationship with the lipid or HDL-bound forms of the protein, has not been established. We used multiple biophysical techniques, including SAXS, TEM, SEC-MALS, native gel electrophoresis, glutaraldehyde crosslinking, and trypsin digestion to characterize the lipid-free and lipid-bound forms of SAA. SAXS and TEM data show the presence of soluble octamers of SAA with structural similarity to the ring-like structures reported for lipid-free ApoA-I. These SAA octamers represent a previously uncharacterized structure for lipid-free SAA and are capable of scaffolding lipid nanodiscs with similar morphology to those formed by ApoA-I. SAA-lipid nanodiscs contain four SAA molecules and have similar exterior dimensions as the lipid-free SAA octamer, suggesting that relatively few conformational rearrangements are required for lipid binding. This study suggests a new model for SAA-lipid interactions and provides new insight into the ability of SAA to stabilize protein-lipid nanodiscs or even replace ApoA-I on HDL particles during inflammation.

biochemistry↗