Editing Secretion (section)

==={{anchor|T4SS}}Type IV secretion system (T4SS or TFSS)===
{{Infobox protein family
| Symbol = T4SS
| Name = T4SS
| image = Image:T4SS.svg
| width =
| caption = Type IV secretion system
| Pfam = PF07996
| Pfam_clan =
| InterPro = IPR012991
| SMART =
| PROSITE =
| MEROPS =
| SCOP = 1gl7
| TCDB = 3.A.7
| OPM family = 215
| OPM protein = 3jqo
| CAZy =
| CDD =
}}

{{Main|Type IV secretion system}}
It is homologous to [[Bacterial conjugation|conjugation]] machinery of bacteria, the [[conjugative pili]]. It is capable of transporting both DNA and proteins. It was discovered in ''Agrobacterium tumefaciens'', which uses this system to introduce the T-DNA portion of the Ti plasmid into the plant host, which in turn causes the affected area to develop into a crown gall (tumor). ''[[Helicobacter pylori]]'' uses a type IV secretion system to deliver [[CagA]] into gastric epithelial cells, which is associated with gastric carcinogenesis.<ref name="pmid16367902">{{cite journal | vauthors = Hatakeyama M, Higashi H | title = Helicobacter pylori CagA: a new paradigm for bacterial carcinogenesis | journal = Cancer Science | volume = 96 | issue = 12 | pages = 835–43 | date = December 2005 | pmid = 16367902 | doi = 10.1111/j.1349-7006.2005.00130.x | s2cid = 5721063 | doi-access = free | pmc = 11159386 }}</ref> ''[[Bordetella pertussis]]'', the causative agent of whooping cough, secretes the [[pertussis toxin]] partly through the type IV system. ''[[Legionella pneumophila]]'', the causing agent of legionellosis (Legionnaires' disease) utilizes a [[type IVB secretion system]], known as the icm/dot ('''i'''ntra'''c'''ellular '''m'''ultiplication / '''d'''efect in '''o'''rganelle '''t'''rafficking genes) system, to translocate numerous [[Bacterial effector protein|effector proteins]] into its eukaryotic host.<ref name="pmid15035043">{{cite journal | vauthors = Cascales E, Christie PJ | title = The versatile bacterial type IV secretion systems | journal = Nature Reviews. Microbiology | volume = 1 | issue = 2 | pages = 137–49 | date = November 2003 | pmid = 15035043 | pmc = 3873781 | doi = 10.1038/nrmicro753 }}</ref> The prototypic Type IVA secretion system is the VirB complex of ''[[Agrobacterium tumefaciens]]''.<ref name="pmid16153176">{{cite journal | vauthors = Christie PJ, Atmakuri K, Krishnamoorthy V, Jakubowski S, Cascales E | title = Biogenesis, architecture, and function of bacterial type IV secretion systems | journal = Annual Review of Microbiology | volume = 59 | pages = 451–85 | year = 2005 | pmid = 16153176 | pmc = 3872966 | doi = 10.1146/annurev.micro.58.030603.123630 }}</ref>

Protein members of this family are components of the type IV secretion system. They mediate [[intracellular]] transfer of [[macromolecule]]s via a [[Nuclear receptor#Mechanism of action|mechanism]] ancestrally related to that of [[bacterial conjugation]] machineries.<ref name="pmid15546668">{{cite journal | vauthors = Christie PJ | title = Type IV secretion: the Agrobacterium VirB/D4 and related conjugation systems | journal = Biochimica et Biophysica Acta (BBA) - Molecular Cell Research | volume = 1694 | issue = 1–3 | pages = 219–34 | date = November 2004 | pmid = 15546668 | pmc = 4845649 | doi = 10.1016/j.bbamcr.2004.02.013 }}</ref><ref name="pmid14673074">{{cite journal | vauthors = Yeo HJ, Yuan Q, Beck MR, Baron C, Waksman G | title = Structural and functional characterization of the VirB5 protein from the type IV secretion system encoded by the conjugative plasmid pKM101 | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 100 | issue = 26 | pages = 15947–52 | date = December 2003 | pmid = 14673074 | pmc = 307673 | doi = 10.1073/pnas.2535211100 | bibcode = 2003PNAS..10015947Y | jstor = 3149111 | doi-access = free }}</ref>

====Function====
The Type IV secretion system (T4SS) is the general mechanism by which bacterial cells secrete or take up macromolecules. Their precise mechanism remains unknown. T4SS is encoded on [[Gram negative bacteria|Gram-negative]] conjugative elements in [[bacteria]]. T4SS are cell envelope-spanning complexes, or, in other words, 11–13 core proteins that form a channel through which DNA and proteins can travel from the cytoplasm of the donor cell to the cytoplasm of the recipient cell. T4SS also secrete [[virulence]] factor proteins directly into host cells as well as taking up DNA from the medium during natural [[Transformation (bacteria)|transformation]].<ref name="pmid12855161">{{cite journal | vauthors = Lawley TD, Klimke WA, Gubbins MJ, Frost LS | title = F factor conjugation is a true type IV secretion system | journal = FEMS Microbiology Letters | volume = 224 | issue = 1 | pages = 1–15 | date = July 2003 | pmid = 12855161 | doi = 10.1016/S0378-1097(03)00430-0 | doi-access = free }}</ref>

====Structure====
As shown in the above figure, TraC, in particular consists of a three helix bundle and a loose globular appendage.<ref name="pmid14673074" />

====Interactions====
T4SS has two effector proteins: firstly, ATS-1, which stands for Anaplasma translocated substrate 1, and secondly [[Ankyrin repeat|AnkA]], which stands for ankyrin repeat domain-containing protein A. Additionally, T4SS coupling proteins are VirD4, which bind to VirE2.<ref name="pmid20670295">{{cite journal | vauthors = Rikihisa Y, Lin M, Niu H | title = Type IV secretion in the obligatory intracellular bacterium Anaplasma phagocytophilum | journal = Cellular Microbiology | volume = 12 | issue = 9 | pages = 1213–21 | date = September 2010 | pmid = 20670295 | pmc = 3598623 | doi = 10.1111/j.1462-5822.2010.01500.x }}</ref>