title: S-layers at second glance? Altiarchaeal grappling hooks (hami) resemble archaeal S-layer proteins in structure and sequence.
abstract: The uncultivated "Candidatus Altiarchaeum hamiconexum" (formerly known as SM1 Euryarchaeon) carries highly specialized nano-grappling hooks ("hami") on its cell surface. Until now little is known about the major protein forming these structured fibrous cell surface appendages, the genes involved or membrane anchoring of these filaments. These aspects were analyzed in depth in this study using environmental transcriptomics combined with imaging methods. Since a laboratory culture of this archaeon is not yet available, natural biofilm samples with high Ca. A. hamiconexum abundance were used for the entire analyses. The filamentous surface appendages spanned both membranes of the cell, which are composed of glycosyl-archaeol. The hami consisted of multiple copies of the same protein, the corresponding gene of which was identified via metagenome-mapped transcriptome analysis. The hamus subunit proteins, which are likely to self-assemble due to their predicted beta sheet topology, revealed no similiarity to known microbial flagella-, archaella-, fimbriae- or pili-proteins, but a high similarity to known S-layer proteins of the archaeal domain at their N-terminal region (44-47% identity). Our results provide new insights into the structure of the unique hami and their major protein and indicate their divergent evolution with S-layer proteins.
authors.affiliation: Department of Internal Medicine, Medical University of Graz Graz, Austria ; Department of Microbiology and Archaea Center, University of Regensburg Regensburg, Germany.
authors.forename: Alexandra K
authors.initials: AK
authors.lastname: Perras
authors.affiliation: Department of Structural Biology, Max Planck Institute of Biophysics Frankfurt, Germany.
authors.forename: Bertram
authors.initials: B
authors.lastname: Daum
authors.affiliation: Department of Biophysics, University of Regensburg Regensburg, Germany.
authors.forename: Christine
authors.initials: C
authors.lastname: Ziegler
authors.affiliation: Chemical Sciences Division, Lawrence Berkeley National Laboratory Berkeley, CA, USA.
authors.forename: Lynelle K
authors.initials: LK
authors.lastname: Takahashi
authors.affiliation: Chemical Sciences Division, Lawrence Berkeley National Laboratory Berkeley, CA, USA.
authors.forename: Musahid
authors.initials: M
authors.lastname: Ahmed
authors.affiliation: Faculty of Biology, Ludwig-Maximilians-University of Munich Munich, Germany.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Wanner
authors.affiliation: Faculty of Biology, Ludwig-Maximilians-University of Munich Munich, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Klingl
authors.affiliation: Research Unit Electron Microscopic Techniques, Institute of Cell Biology, Histology and Embryology, Medical University of Graz Graz, Austria.
authors.forename: Gerd
authors.initials: G
authors.lastname: Leitinger
authors.affiliation: Institute of Cell Biology, Histology and Embryology, Medical University of Graz Graz, Austria ; Core Facility Ultrastructure, Analysis, Center for Medical Research Institute, Medical University of Graz Graz, Austria.
authors.forename: Dagmar
authors.initials: D
authors.lastname: Kolb-Lenz
authors.affiliation: Unité Biologie Moléculaire du Gene chez les Extrêmophiles, Departément de Microbiologie, Institut Pasteur Paris, France.
authors.forename: Simonetta
authors.initials: S
authors.lastname: Gribaldo
authors.affiliation: Department of Microbiology and Archaea Center, University of Regensburg Regensburg, Germany.
authors.forename: Anna
authors.initials: A
authors.lastname: Auerbach
authors.affiliation: Department of Internal Medicine, Medical University of Graz Graz, Austria.
authors.forename: Maximilian
authors.initials: M
authors.lastname: Mora
authors.affiliation: Department of Earth and Planetary Science, University of California, Berkeley Berkeley, CA, USA.
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Probst
authors.affiliation: Department of Microbiology and Archaea Center, University of Regensburg Regensburg, Germany.
authors.forename: Annett
authors.initials: A
authors.lastname: Bellack
authors.affiliation: Department of Internal Medicine, Medical University of Graz Graz, Austria ; Department of Microbiology and Archaea Center, University of Regensburg Regensburg, Germany ; BioTechMed-Graz Graz, Austria.
authors.forename: Christine
authors.initials: C
authors.lastname: Moissl-Eichinger
keywords: S-layers; archaea; archaeal cell surface appendages; double-membrane; electron cryo-tomography; environmental transcriptomics; hami; nano-grappling hooks