title: Two novel heat-soluble protein families abundantly expressed in an anhydrobiotic tardigrade.
abstract: Tardigrades are able to tolerate almost complete dehydration by reversibly switching to an ametabolic state. This ability is called anhydrobiosis. In the anhydrobiotic state, tardigrades can withstand various extreme environments including space, but their molecular basis remains largely unknown. Late embryogenesis abundant (LEA) proteins are heat-soluble proteins and can prevent protein-aggregation in dehydrated conditions in other anhydrobiotic organisms, but their relevance to tardigrade anhydrobiosis is not clarified. In this study, we focused on the heat-soluble property characteristic of LEA proteins and conducted heat-soluble proteomics using an anhydrobiotic tardigrade. Our heat-soluble proteomics identified five abundant heat-soluble proteins. All of them showed no sequence similarity with LEA proteins and formed two novel protein families with distinct subcellular localizations. We named them Cytoplasmic Abundant Heat Soluble (CAHS) and Secretory Abundant Heat Soluble (SAHS) protein families, according to their localization. Both protein families were conserved among tardigrades, but not found in other phyla. Although CAHS protein was intrinsically unstructured and SAHS protein was rich in β-structure in the hydrated condition, proteins in both families changed their conformation to an α-helical structure in water-deficient conditions as LEA proteins do. Two conserved repeats of 19-mer motifs in CAHS proteins were capable to form amphiphilic stripes in α-helices, suggesting their roles as molecular shield in water-deficient condition, though charge distribution pattern in α-helices were different between CAHS and LEA proteins. Tardigrades might have evolved novel protein families with a heat-soluble property and this study revealed a novel repertoire of major heat-soluble proteins in these anhydrobiotic animals.
authors.affiliation: Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Tokyo, Japan.
authors.forename: Ayami
authors.initials: A
authors.lastname: Yamaguchi
authors.forename: Sae
authors.initials: S
authors.lastname: Tanaka
authors.forename: Shiho
authors.initials: S
authors.lastname: Yamaguchi
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Kuwahara
authors.forename: Chizuko
authors.initials: C
authors.lastname: Takamura
authors.forename: Shinobu
authors.initials: S
authors.lastname: Imajoh-Ohmi
authors.forename: Daiki D
authors.initials: DD
authors.lastname: Horikawa
authors.forename: Atsushi
authors.initials: A
authors.lastname: Toyoda
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Katayama
authors.forename: Kazuharu
authors.initials: K
authors.lastname: Arakawa
authors.forename: Asao
authors.initials: A
authors.lastname: Fujiyama
authors.forename: Takeo
authors.initials: T
authors.lastname: Kubo
authors.forename: Takekazu
authors.initials: T
authors.lastname: Kunieda
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003681:Dehydration / Q000378:metabolism*; D017433:Protein Structure, Secondary; D011506:Proteins / Q000378:metabolism*; D040901:Proteomics; D058467:Tardigrada / Q000378:metabolism*
chemical_list: D011506:Proteins