Editing Periplasm (section)

== Function ==
In [[diderm bacteria]], the periplasm contains a thin [[cell wall]] composed of [[peptidoglycan]]. In addition, it includes solutes such as ions and proteins, which are involved in wide variety of functions ranging from nutrient binding, transport, folding, degradation, substrate hydrolysis, to peptidoglycan synthesis, [[electron transport]], and alteration of substances toxic to the cell ([[xenobiotic metabolism]]).<ref name="isbn0-07-295175-3">{{cite book | vauthors = Klein DW, Prescott LM, Harley J |title=Microbiology |publisher=McGraw-Hill Higher Education |location=Boston |year=2005 |isbn=0-07-295175-3 }}</ref> Importantly, the periplasm is devoid of [[adenosine triphosphate|ATP]]. Several types of enzyme are present in the periplasm including [[alkaline phosphatase]]s, [[Cyclic nucleotide phosphodiesterase|cyclic phosphodiesterase]]s, [[acid phosphatase]]s and [[5'-nucleotidase|5’-nucleotidase]]s.<ref>{{cite journal | vauthors = Neu HC, Heppel LA | title = The release of enzymes from Escherichia coli by osmotic shock and during the formation of spheroplasts | journal = The Journal of Biological Chemistry | volume = 240 | issue = 9 | pages = 3685–3692 | date = September 1965 | pmid = 4284300 | doi = 10.1016/S0021-9258(18)97200-5 | doi-access = free }}</ref> Of note, the periplasm also contains enzymes important for the facilitation of [[protein folding]]. For example, disulfide bond protein A (DsbA) and disulfide bond protein C (DsbC), which are responsible for catalyzing peptide bond formation and isomerization, respectively, were identified in the periplasm of ''[[Escherichia coli|E. Coli]].''<ref>{{cite journal | vauthors = Denoncin K, Collet JF | title = Disulfide bond formation in the bacterial periplasm: major achievements and challenges ahead | journal = Antioxidants & Redox Signaling | volume = 19 | issue = 1 | pages = 63–71 | date = July 2013 | pmid = 22901060 | pmc = 3676657 | doi = 10.1089/ars.2012.4864 }}</ref> As disulfide bond formation is frequently a rate-limiting step in the folding of proteins, these oxidizing enzymes play an important role in the bacteria periplasm. In addition, the periplasm mediates the uptake of DNA in several strains of transformable bacteria.<ref name="Hahn_2021">{{cite journal | vauthors = Hahn J, DeSantis M, Dubnau D | title = Mechanisms of Transforming DNA Uptake to the Periplasm of Bacillus subtilis | journal = mBio | volume = 12 | issue = 3 | pages = e0106121 | date = June 2021 | pmid = 34126763 | pmc = 8262900 | doi = 10.1128/mBio.01061-21 | veditors = Freitag NE }}</ref> 
[[File:Rcsfsignalingmechanism.jpg|thumb|Figure demonstrating modulation of RcsF signaling by changes in the periplasmic intermembrane distance<ref name="Miller_2018"/>]]
The compartmentalization afforded by the periplasmic space gives rise to several important functions. Aside from those previously mentioned, the periplasm also functions in protein transport and quality control, analogous to the [[endoplasmic reticulum]] in eukaryotes.<ref name="Miller_2018">{{cite journal | vauthors = Miller SI, Salama NR | title = The gram-negative bacterial periplasm: Size matters | journal = PLOS Biology | volume = 16 | issue = 1 | pages = e2004935 | date = January 2018 | pmid = 29342145 | pmc = 5771553 | doi = 10.1371/journal.pbio.2004935 | doi-access = free }}</ref> Furthermore, the separation of the periplasm from the cytoplasm allows for the compartmentalization of enzymes that could be toxic in the cytoplasm.<ref name="Miller_2018" /> Some [[peptidoglycan]]s and [[lipoprotein]]s located in the periplasm provide a structural support system for the cell that aids in promoting the cell's ability to withstand turgor pressure. Notably, organelles such as the [[flagellum]] require the assembly of polymers within the periplasm for proper functioning. As the driveshaft of the flagellum spans the periplasmic space, its length is dictated by positioning of the outer membrane as induced by its contraction, which is mediated by periplasmic polymers.<ref name="Miller_2018" /> The periplasm also functions in [[cell signaling]], such as in the case of the lipoprotein RcsF, which has a globular domain residing in the periplasm and acts as a stress sensor. When RcsF fails to interact with BamA, such as in the case of an enlarged periplasm, RcsF is not exported to the cell surface and are able to trigger the Rcs signaling cascade. Periplasm size, therefore, plays an important role in stress signaling.<ref>{{cite journal | vauthors = Rodríguez-Alonso R, Létoquart J, Nguyen VS, Louis G, Calabrese AN, Iorga BI, Radford SE, Cho SH, Remaut H, Collet JF | display-authors = 6 | title = Structural insight into the formation of lipoprotein-β-barrel complexes | journal = Nature Chemical Biology | volume = 16 | issue = 9 | pages = 1019–1025 | date = September 2020 | pmid = 32572278 | pmc = 7610366 | doi = 10.1038/s41589-020-0575-0 }}</ref><ref name="Miller_2018" />