# Divergent roles of Hsp70 chaperones in orthoflavivirus protein secretion and virion formation

## TL;DR

This study explores how Hsp70 chaperones help orthoflaviviruses like TBEV and WNV produce proteins and form infectious particles, suggesting new antiviral strategies.

## Contribution

The study reveals distinct roles of Hsp70 and BiP in orthoflavivirus protein secretion and infectivity, offering new insights into antiviral drug development.

## Key findings

- Hsp70 and BiP contribute differently to orthoflavivirus protein secretion and infectivity.
- Inhibitor YM-1 reduces infectivity of multiple orthoflaviviruses.
- BiP is essential for NS1 secretion in tick-borne orthoflaviviruses but not for infectivity.

## Abstract

Orthoflaviviruses, such as tick-borne encephalitis virus (TBEV) and West Nile virus (WNV), can cause severe neurological disease and remain without specific antiviral treatments. We found that orthoflavivirus envelope (E) and non-structural protein 1 (NS1) interact with heat shock protein 70 (Hsp70) chaperones, key regulators of protein homeostasis and existing cancer drug targets. We examined how Hsp70 and endoplasmic reticulum–resident BiP contribute to viral protein secretion and infectivity of tick and mosquito-borne orthoflaviviruses. Targeting the Hsp70 nucleotide-binding domain with small-molecule inhibitor YM-1 significantly reduced infectivity of multiple orthoflaviviruses, while substrate-binding domain inhibitor PES-Cl specifically impaired NS1 secretion of tick-borne orthoflaviviruses. Protein degradation inhibitors restored NS1 expression in BiP-deficient cells but failed to rescue NS1 secretion. These data indicate that while BiP is essential for secretion of tick-borne orthoflavivirus NS1, it is not required for infectivity. The antiviral effect of YM-1 likely reflects inhibition of other chaperones or additional cellular targets.