Editing S-layer (section)

{{Short description|Protein-based part of the cell envelope found in most archaea and some bacteria}}
An '''S-layer''' (surface layer) is a part of the [[cell envelope]] found in almost all [[archaea]], as well as in many types of [[bacteria]].<ref name="Albers2011">{{cite journal |vauthors=Albers SV, Meyer BH |date=2011 |title=The archaeal cell envelope |journal=Nature Reviews Microbiology |volume=9 |issue= 6|pages=414–426 |doi=10.1038/nrmicro2576 |pmid=21572458 |s2cid=10297797 }}</ref><ref name= "Sleytr2014" >{{cite journal |vauthors = Sleytr UB, Schuster B, Egelseer EM, Pum D |date=2014 |title=S-layers: Principles and Applications |journal=FEMS Microbiology Reviews |volume=38 |issue=5 |pages=823–864 |doi=10.1111/1574-6976.12063 |pmc=4232325 |pmid=24483139 }}</ref><ref name= "Sleytr2025" >{{cite journal | vauthors = Sleytr UB, Pum D | date = 2025 | title = S-layers: from a serendipitous discovery to a toolkit for nanobiotechnology | journal = Quarterly Reviews of Biophysics | volume = 58 | issue = e4 | pages = e4 | doi=10.1017/S0033583524000106 | pmid = 39819733 }}</ref>
The S-layers of both archaea and bacteria consists of a [[Monolayer|monomolecular layer]] composed of only one (or, in a few cases, two) identical [[proteins]] or [[glycoproteins]].<ref name="Sleytr2014" /><ref name="Sleytr2025" /><ref>{{Cite journal|last1=Rodrigues-Oliveira|first1=Thiago|last2=Belmok|first2=Aline|last3=Vasconcellos|first3=Deborah|last4=Schuster|first4=Bernhard|last5=Kyaw|first5=Cynthia M.|date=2017-12-22|title=Archaeal S-Layers: Overview and Current State of the Art|journal=Frontiers in Microbiology|volume=8|page=2597|doi=10.3389/fmicb.2017.02597|issn=1664-302X|pmc=5744192|pmid=29312266|doi-access=free}}</ref> This structure is built via [[self-assembly]] and encloses the whole cell surface. Thus, the S-layer protein can represent up to 15% of the whole protein content of a cell.<ref name = "Sleytr1993">{{cite journal |vauthors=Sleytr U, Messner P, Pum D, Sára M |title=Crystalline bacterial cell surface layers |journal=Mol. Microbiol. |volume=10 |issue=5 |pages=911–6 |year=1993 |pmid=7934867 |doi=10.1111/j.1365-2958.1993.tb00962.x|s2cid=86119414 }}</ref> S-layer proteins are poorly conserved or not conserved at all, and can differ markedly even between related species.  Depending on species, the S-layers have a thickness between 5 and 25&nbsp;nm and possess identical pores 2–8&nbsp;nm in diameter.<ref name="Sleytr2014" /><ref name="Sleytr2025" /><ref name="Sleytr2016" /><ref name= " Buhlheller2024" >{{cite journal | vauthors=Buhlheller C, Sagmeister T, Grininger C, Gubensak N, Sleytr UB, Uson I, Pavkov-Keller T| date = 2024 | title = SymProFold: Structural prediction of symmetrical biological assemblies | journal = Nat Commun | volume = 15 | issue = 1| page = 8152 | doi=10.1038/s41467-024-52138-3| pmid = 39294115 | bibcode = 2024NatCo..15.8152B | hdl = 10261/372119 | hdl-access = free }}</ref>

The terminology "S-layer" was used the first time in 1976.<ref name="Sleytr1976">{{cite journal |author=Sleytr UB |date=1976 |title=Self-assembly of the hexagonally and tetragonally arranged subunits of bacterial surface layers and their reattachment to cell walls |journal=J. Ultrastruct. Res. |volume=55 |issue=3 |pages=360–367 |doi=10.1016/S0022-5320(76)80093-7 |pmid=6800 }}</ref> The general use was accepted at the "First International Workshop on Crystalline Bacterial Cell Surface Layers, Vienna (Austria)" in 1984, and in the year 1987 S-layers were defined at the [[European Molecular Biology Organization]] Workshop on "Crystalline Bacterial Cell Surface Layers", Vienna as "Two-dimensional arrays of proteinaceous subunits forming surface layers on prokaryotic cells" (see "Preface", page VI in Sleytr "et al. 1988"<ref name="Sleytr1988">{{cite book |vauthors=Sleytr UB, Messner P, Pum D, Sára M |editor1-first=Uwe B |editor1-last=Sleytr |editor2-first=Paul |editor2-last=Messner |editor3-first=Dietmar |editor3-last=Pum |editor4-first=Margit |editor4-last=Sára |date=1988 |title=Crystalline Bacterial Cell Surface Layers |url=https://www.springer.com/de/book/9783642735394 |location=Berlin |publisher=Springer |doi=10.1007/978-3-642-73537-0 |isbn=978-3-540-19082-0 |s2cid=20244135 }}</ref>). For a brief summary on the history of S-layer research see "References"''.''<ref name="Sleytr2014" /><ref name="Sleytr2016">{{cite book |author=Sleytr UB |date=2016 |title=Curiosity and Passion for Science and Art |volume=7 |location=Singapore |publisher=World Scientific Publishing |isbn=978-981-3141-81-0 |doi=10.1142/10084 |series=Series in Structural Biology }}</ref>A comprehensive historical account of the development of fundamental and applied S-layer research is given in the following current review.<ref name="Sleytr2025" />