# Multiple origins and functions: evolutionary pathways of HSP70 proteins in viruses

## TL;DR

This study explores the evolutionary origins and functions of HSP70 proteins in viruses, revealing multiple independent acquisitions and distinct evolutionary pathways.

## Contribution

The study identifies HSP70 homologues in viruses with diverse genome types and provides insights into their evolutionary origins and functional adaptations.

## Key findings

- HSP70 homologues were found in viruses with dsDNA genomes, including up to three gene copies per genome in Megaviricetes.
- Structural and phylogenetic analyses suggest horizontal gene transfer from protist hosts for dsDNA virus HSP70s.
- ssRNA virus HSP70s form a distinct evolutionary group with higher sequence and structural diversity.

## Abstract

Heat shock protein 70s (HSP70s) are highly conserved molecular chaperones found across all domains of life, where they play essential roles in cellular stress responses. Whilst HSP70 homologues have been previously identified in closteroviruses that have ssRNA genomes, their broader presence and evolutionary history in viruses remain poorly understood. In this study, we conducted a comprehensive search of viral protein databases and identified HSP70 homologues in viruses beyond those with ssRNA genomes, including examples with dsDNA genomes in the class Megaviricete. These viral HSP70s exhibit diverse gene organizations, copy numbers and structural features. Notably, HSP70s of viruses from Megaviricetes showed up to three gene copies per genome and distinct structural motifs, whilst those from closteroviruses displayed higher sequence and structural diversity, suggesting faster evolutionary rates. Structural and phylogenetic analyses revealed two major clusters of viral HSP70s, with dsDNA virus HSP70s closely resembling those of their protist hosts, supporting the hypothesis of horizontal gene transfer. In contrast, ssRNA virus HSP70s formed a distinct, highly divergent group. Our findings suggest multiple independent acquisitions of HSP70 genes by viruses and provide new insights into their evolutionary trajectories and potential functional adaptations.