Helicity of a tardigrade disordered protein contributes to its protective function during desiccation

Abstract

In order to survive extreme drying (anhydrobiosis), many organisms, spanning every kingdom of life, accumulate intrinsically disordered proteins (IDPs). For decades, the ability of anhydrobiosis‐related IDPs to form transient amphipathic helices has been suggested to be important for promoting desiccation tolerance. However, evidence empirically supporting the necessity and/or sufficiency of helicity in mediating anhydrobiosis is lacking. Here we demonstrate that the linker region of CAHS D, a desiccation‐related IDP from the tardigrade Hypsibius exemplaris, that contains significant helical structure, is the protective portion of this protein. Perturbing the sequence composition and grammar of the linker region of CAHS D, through the insertion of helix‐breaking prolines, modulating the identity of charged residues, or replacement of hydrophobic amino acids with serine or glycine residues results in variants with different degrees of helical structure. Importantly, correlation of protective capacity and helical content in variants generated through different helix perturbing modalities do not show as strong a trend, suggesting that while helicity is important it is not the only property that makes a protein protective during desiccation. These results provide direct evidence for the decades old theory that helicity of desiccation‐related IDPs is linked to their anhydrobiotic capacity.This article is protected by copyright. All rights reserved.

Labile assembly of a tardigrade protein induces biostasis

“…This variant does not slow metabolism, which suggests that CAHS D is capable of conferring protection against hyperosmotic stress at the cellular level in both in condensed and uncondensed form, likely through distinct mechanisms. This is in line with previous in vitro studies which show that gelling and non-gelling variants of CAHS D protect labile proteins to varying degrees during desiccation (Biswas et al, 2024;Hesgrove et al, 2021;Packebush et al, 2023). In its non-condensed form, CAHS D might confer protection to cells undergoing hyperosmotic stress through the prevention of protein aggregation via molecular shielding and/or stabilization of membranes via helical absorption (Hesgrove & Boothby, 2020).…”