Editing S-layer (section)

== Biological functions of the S-layer ==
For many bacteria, the S-layer represents the outermost interaction zone with their respective environment.<ref name="Sleytr2014" /><ref name="Sleytr2025" /><ref name="Sleytr1999">{{cite journal|last1=Sleytr|first1=UB|last2=Beveridge|first2=TJ|title=Bacterial S-layers|journal=Trends Microbiol.|volume=7|issue=6|pages=253–260|year=1999|pmid=10366863|doi=10.1016/s0966-842x(99)01513-9}}</ref> Its functions are very diverse and vary from species to species. In many archaeal species the S-layer is the only cell wall component and, therefore, is important for mechanical and osmotic stabilization.<ref name="Sleytr2014" /><ref name="Sleytr2025" /><ref>{{Cite journal |last1=Pfeifer |first1=Kevin |last2=Ehmoser |first2=Eva-Kathrin |last3=Rittmann |first3=Simon K.-M. R. |last4=Schleper |first4=Christa |last5=Pum |first5=Dietmar |last6=Sleytr |first6=Uwe B. |last7=Schuster |first7=Bernhard |date=2022-07-21 |title=Isolation and Characterization of Cell Envelope Fragments Comprising Archaeal S-Layer Proteins |journal=Nanomaterials |language=en |volume=12 |issue=14 |page=2502 |doi=10.3390/nano12142502 |pmid=35889727 |pmc=9320373 |issn=2079-4991 |doi-access=free }}</ref> The S-layer is considered to be porous, which contributes to many of its functions.<ref name="Sleytr2014" /><ref name="Sleytr2025" /><ref name="Buhlheller2024" /> A most relevant general function of S-layers of both, bacteria and archaea, seems to be their excellent anti-fouling properties.<ref name="Sleytr2014" /><ref name="Sleytr2025" /><ref name="Rothbauer2013">{{cite journal |vauthors=Rothbauer M, Küpcü S, Sticker D, Sleytr UB, Ertl P |date=2013 |title=Exploitation of S-layer Anisotropy: pH-dependent Nanolayer Orientation for Cellular Micropatterning |journal=ACS Nano |volume=7 |issue=9 |pages=8020–8030 |doi=10.1021/nn403198a |pmid=24004386 }}</ref> In Archaea that possess S-Layers as the exclusive cell wall component, a general function of S-layer lattices is that of a cell shape-determining/maintaining scaffold.<ref name="Pum1991" /><ref name= "Messner1986" >{{cite journal | vauthors = Messner P, Pum D, Sára M, Stetter KO, Sleytr UB | date = 1986 | title = Ultrastructure of the cell envelope of the archaebacteria ''Thermoproteus tenax'' and ''Thermoproteus neutrophilus'' | journal = J. Bacteriol. | volume = 166 | issue = 3 | pages = 1046–1054| doi=10.1128/jb.166.3.1046-1054.1986| pmid = 3086286 | pmc = 215230 }}</ref><ref name= "Zink2019" >{{cite journal | vauthors = Zink IA, Pfeifer K, Wimmer E, Sleytr UB, Schuster B, Schleper C | date = 2019 | title = CRISPR-mediated gene silencing reveals involvement of the archaeal S-layer in cell division and virus infection | journal = Nat. Commun. | volume = 10 | page = 4797| doi=10.1038/s41467-019-12745-x | pmid = 31641111 | pmc = 6805947 | bibcode = 2019NatCo..10.4797Z }}</ref> For an overview of functions of S-layers, see.<ref name="Sleytr2014" /><ref name="Sleytr2025" /> The spectrum  of functions associated with S-layers include:
* protection against [[bacteriophages]], [[Bdellovibrio]]s, and [[phagocytosis]]
* resistance against low [[pH]]
* barrier against high-molecular-weight substances (e.g., lytic [[enzymes]])
* adhesion (for [[glycosylated]] S-layers)
* stabilization of the membrane (e.g. the SDBC in ''[[Deinococcus radiodurans]]'') <ref name="Farci2016">{{cite journal |vauthors=Farci D, Slavov C, Tramontano E, Piano D |date=2016 |title=The S-layer Protein DR_2577 Binds Deinoxanthin and under Desiccation Conditions Protects against UV-Radiation in Deinococcus radiodurans |journal=Frontiers in Microbiology |volume=7 |page=155 |doi=10.3389/fmicb.2016.00155 |pmid=26909071 |pmc=4754619 |doi-access=free }}</ref><ref name="Farci2018">{{cite journal |vauthors=Farci D, Slavov C, Piano D |date=2018 |title=Coexisting properties of thermostability and ultraviolet radiation resistance in the main S-layer complex of Deinococcus radiodurans |journal=Photochem Photobiol Sci |volume=17 |issue=1 |pages=81–88 |doi=10.1039/c7pp00240h |pmid=29218340 |bibcode=2018PcPbS..17...81F |doi-access=free }}</ref>
* resistance against electromagnetic stress (e.g. ionizing radiations and high temperatures) <ref name="Farci2016">{{cite journal |vauthors=Farci D, Slavov C, Tramontano E, Piano D |date=2016 |title=The S-layer Protein DR_2577 Binds Deinoxanthin and under Desiccation Conditions Protects against UV-Radiation in Deinococcus radiodurans |journal=Frontiers in Microbiology |volume=7 |page=155 |doi=10.3389/fmicb.2016.00155 |pmid=26909071 |pmc=4754619 |doi-access=free }}</ref><ref name="Farci2018">{{cite journal |vauthors=Farci D, Slavov C, Piano D |date=2018 |title=Coexisting properties of thermostability and ultraviolet radiation resistance in the main S-layer complex of Deinococcus radiodurans |journal=Photochem Photobiol Sci |volume=17 |issue=1 |pages=81–88 |doi=10.1039/c7pp00240h |pmid=29218340 |bibcode=2018PcPbS..17...81F |doi-access=free }}</ref>
* provision of adhesion sites for exoproteins <ref name= "Egelseer1995" >{{cite journal |vauthors = Egelseer E, Schocher I, Sára M, Sleytr UB |date = 1995 | title= The S-layer from Bacillus stearothermophilus DSM 2358 functions as adhesion site for a high-molecular-weight amylase | journal = J Bacteriol | volume = 177 | issue = 6 | pages = 1444–1451 | doi=10.1128/jb.177.6.1444-1451.1995 |pmid = 7533757 | pmc = 176758 }}</ref>
* provision of a periplasmic compartment in Gram-positive prokaryotes together with the peptidoglycan and the cytoplasmic membranes <ref name="Sleytr1999" />
* biomineralization<ref name="Schultzelam1992">{{cite journal |vauthors=Schultze-Lam S, Harauz G, Beveridge TJ |date=1992 |title=Participation of a cyanobacterial S layer in fine-grain mineral formation|journal=J. Bacteriol. |volume=174 |issue=24 |pages=7971–7981 |doi=10.1128/jb.174.24.7971-7981.1992 |pmid=1459945 |pmc=207533 }}</ref><ref name="Shenton1997">{{cite journal |vauthors=Shenton W, Pum D, Sleytr UB, Mann S |date=1997 |title=Synthesis of CdS superlattices using self-assembled bacterial S-layers |journal=Nature |volume=389 |issue= 6651|pages=585–587 |doi=10.1038/39287 |s2cid=4317884 }}</ref><ref name="Mertig1999">{{cite journal |vauthors=Mertig M, Kirsch R, Pompe W, Engelhardt H |date=1999 |title=Fabrication of highly oriented nanocluster arrays by biomolecular templating |journal=Eur. Phys. J. D |volume=9 |issue=1 |pages=45–48 |doi=10.1007/s100530050397 |bibcode=1999EPJD....9...45M |s2cid=120507258 }}</ref>
* molecular sieve and barrier function<ref name="Sleytr2014"/><ref name="Sara1987">{{cite journal |vauthors=Sára M, Sleytr, UB |date=1987 |title=  Production and characteristics of ultrafiltration membranes with uniform pores from two-dimensional arrays of proteins |journal=J. Membr. Sci. |volume=33 |issue=1  |pages=27–49 |doi=10.1016/S0376-7388(00)80050-2 }}</ref><ref>{{cite journal |last1=von Kügelgen |first1=Andriko |last2=Cassidy |first2=C. Keith |last3=van Dorst |first3=Sofie |last4=Pagani |first4=Lennart L. |last5=Batters |first5=Christopher |last6=Ford |first6=Zephyr |last7=Löwe |first7=Jan |last8=Alva |first8=Vikram |last9=Stansfeld |first9=Phillip J. |last10=Bharat |first10=Tanmay A. M. |title=Membraneless channels sieve cations in ammonia-oxidizing marine archaea |journal=Nature |date=6 June 2024 |volume=630 |issue=8015 |pages=230–236 |doi=10.1038/s41586-024-07462-5 |doi-access=free|pmid=38811725 |pmc=11153153 |bibcode=2024Natur.630..230V }}</ref><ref name="Schuster2021">{{cite journal |vauthors=Schuster B, Sleytr UB |date=2021 |title=S-Layer Ultrafiltration Membranes |journal=Membranes |volume=11 |issue=4 |page=275 |doi=10.3390/membranes11040275 |pmid=33918014 |pmc=8068369 |doi-access=free }}</ref>
A great example of a bacterium which utilizes the biological functions of the S-layer is ''Clostridioides difficile.'' In ''C. difficile'', the S-layer has helped with biofilm formation, host cell adhesion, and immunomodulation through cell signaling of the host response.<ref>{{Cite journal |last1=Ormsby |first1=Michael J. |last2=Vaz |first2=Filipa |last3=Kirk |first3=Joseph A. |last4=Barwinska-Sendra |first4=Anna |last5=Hallam |first5=Jennifer C. |last6=Lanzoni-Mangutchi |first6=Paola |last7=Cole |first7=John |last8=Chaudhuri |first8=Roy R. |last9=Salgado |first9=Paula S. |last10=Fagan |first10=Robert P. |last11=Douce |first11=Gillian R. |date=2023-06-29 |title=An intact S-layer is advantageous to Clostridioides difficile within the host |journal=PLOS Pathogens |language=en |volume=19 |issue=6 |pages=e1011015 |doi=10.1371/journal.ppat.1011015 |issn=1553-7374 |pmc=10310040 |pmid=37384772 |doi-access=free }}</ref>