AB toxin

{{Infobox protein family | Symbol = ADPrib_exo_Tox | Name = C2-like exotoxin "A" part | image = PDB 1giq EBI.jpg | width = | caption = Crystal structure of the enzymatic component of iota-toxin from ''Clostridium perfringens'' with NADH | Pfam = PF03496 | Pfam_clan = CL0084 | InterPro = IPR003540 | SMART = | PROSITE = | MEROPS = | SCOP = 1giq | TCDB = | OPM family = | OPM protein = | CAZy = | CDD = }} {{Infobox protein family | Symbol = Binary_toxB | Name = AB7-type toxin, "B" part | image = PDB 1tzo EBI.jpg | width = | caption = crystal structure of the anthrax toxin protective antigen heptameric prepore | Pfam = PF03495 | Pfam_clan = | InterPro = IPR003896 | SMART = | PROSITE = | MEROPS = | SCOP = 1acc | TCDB = 1.C.42 | OPM family = | OPM protein = | CAZy = | CDD = }} The '''AB toxins''' are two-component protein complexes secreted by a number of pathogenic bacteria, though there is a pore-forming AB toxin found in the eggs of a snail.<ref>{{Cite journal |last1=Giglio |first1=M.L. |last2=Ituarte |first2=S. |last3=Milesi |first3=V. |last4=Dreon |first4=M.S. |last5=Brola |first5=T.R. |last6=Caramelo |first6=J. |last7=Ip |first7=J.C.H. |last8=Maté |first8=S. |last9=Qiu |first9=J.W. |last10=Otero |first10=L.H. |last11=Heras |first11=H. |date=August 2020 |title=Exaptation of two ancient immune proteins into a new dimeric pore-forming toxin in snails |url=https://linkinghub.elsevier.com/retrieve/pii/S1047847720301040 |journal=Journal of Structural Biology |language=en |volume=211 |issue=2 |article-number=107531 |doi=10.1016/j.jsb.2020.107531|pmid=32446810 |hdl=11336/143650 |hdl-access=free }}</ref> They can be classified as Type III toxins because they interfere with internal cell function.<ref name="urlBacterial Pathogenesis: Bacterial Factors that Damage the Host - Producing Exotoxins - A-B Toxins">{{cite web|url=http://student.ccbcmd.edu/courses/bio141/lecguide/unit2/bacpath/abtox.html |title=Bacterial Pathogenesis: Bacterial Factors that Damage the Host - Producing Exotoxins - A-B Toxins |access-date=2008-12-13 |archive-url=https://web.archive.org/web/20100727001308/http://student.ccbcmd.edu/courses/bio141/lecguide/unit2/bacpath/abtox.html |archive-date=2010-07-27 }}</ref> They are named AB toxins due to their components: the "A" component is usually the "active" portion, and the "B" component is usually the "binding" portion.<ref name="urlBacterial Pathogenesis: Bacterial Factors that Damage the Host - Producing Exotoxins - A-B Toxins"/><ref name="pmid15204437">{{cite journal |vauthors =De Haan L, Hirst TR |title=Cholera toxin: a paradigm for multi-functional engagement of cellular mechanisms (Review) |journal=Mol. Membr. Biol. |volume=21 |issue=2 |pages=77–92 |year=2004 |pmid=15204437 |doi=10.1080/09687680410001663267 |s2cid=22270979 |doi-access=free }}</ref> The "A" subunit possesses enzyme activity, and is transferred to the host cell following a conformational change in the membrane-bound transport "B" subunit.<ref name="pmid8225592">{{cite journal | vauthors = Perelle S, Gibert M, Boquet P, Popoff MR | title = Characterization of Clostridium perfringens iota-toxin genes and expression in Escherichia coli | journal = Infect. Immun. | volume = 61 | issue = 12 | pages = 5147–56 |date=December 1993 | pmid = 8225592 | pmc = 281295 | doi = 10.1128/IAI.61.12.5147-5156.1993}}</ref>

== Examples ==

* DT-like toxins: all toxins of these class are ADP-ribosyltransferases, which means they damage the cell by attaching an ADP-ribose moiety onto important target components: in this case eEF2.<ref name="pmid25023120">{{cite journal |last1=Simon |first1=NC |last2=Aktories |first2=K |last3=Barbieri |first3=JT |title=Novel bacterial ADP-ribosylating toxins: structure and function. |journal=Nature Reviews. Microbiology |date=September 2014 |volume=12 |issue=9 |pages=599–611 |doi=10.1038/nrmicro3310 |pmid=25023120|pmc=5846498 }}</ref> ** The Diphtheria toxin (DT) is an AB toxin. It inhibits protein synthesis in the host cell through ADP-ribosylation of the eukaryotic elongation factor 2 (eEF2), which is an essential component for protein synthesis. It is slightly unusual in that it combines the A and B parts in the same protein chain: the pre-toxin is cleaved into two parts, then the two parts are joined by a disulfide bond.<ref name="pmid25023120"/> ** The exotoxin A of ''Pseudomonas aeruginosa'' is another example of an AB toxin that targets the eEF2. The "A" part is structurally similar to the DT "A" part; the "B" part is located to the N-terminal direction to the "A" part, unlike DT. The bioinformatically-identified "Cholix" toxin from ''V. cholerae'' is similar.<ref name="pmid25023120"/> * AB7 toxins: all toxins of this class share a related heptameric "B" subunit, but differ in the function of their "A" part.<ref name="pmid8225592" /> ** C2-like toxins: the "A" parts are G-actin ADP-ribosyltransferases, which carry out a modification that prevents actin from polymerizing. Members include ''C. botulinum''<ref name="pmid8645309">{{cite journal | vauthors = Fujii N, Kubota T, Shirakawa S, Kimura K, Ohishi I, Moriishi K, Isogai E, Isogai H | title = Characterization of component-I gene of botulinum C2 toxin and PCR detection of its gene in clostridial species | journal = Biochem. Biophys. Res. Commun. | volume = 220 | issue = 2 | pages = 353–9 |date=March 1996 | pmid = 8645309 | doi = 10.1006/bbrc.1996.0409 }}</ref> ''C. perfringens'' iota toxin and ''Clostridioides difficile'' ADP-ribosyltransferase.<ref name="pmid10802189">{{cite journal | vauthors = Stubbs S, Rupnik M, Gibert M, Brazier J, Duerden B, Popoff M | title = Production of actin-specific ADP-ribosyltransferase (binary toxin) by strains of Clostridium difficile | journal = FEMS Microbiol. Lett. | volume = 186 | issue = 2 | pages = 307–12 |date=May 2000 | pmid = 10802189 | doi = 10.1111/j.1574-6968.2000.tb09122.x| doi-access = free }}</ref><ref name="pmid25023120"/> ** Anthrax toxins: The protective antigen (PA) is the "B" component shared by the two "A" toxins in ''B. anthracis'': the edema factor (EF) and the lethal factor (LF).<ref name="pmid1910002">{{cite journal | vauthors = Pezard C, Berche P, Mock M | title = Contribution of individual toxin components to virulence of Bacillus anthracis | journal = Infect. Immun. | volume = 59 | issue = 10 | pages = 3472–7 |date=October 1991 | pmid = 1910002 | pmc = 258908 | doi = 10.1128/IAI.59.10.3472-3477.1991}}</ref><ref name="pmid3148491">{{cite journal | vauthors = Welkos SL, Lowe JR, Eden-McCutchan F, Vodkin M, Leppla SH, Schmidt JJ | title = Sequence and analysis of the DNA encoding protective antigen of Bacillus anthracis | journal = Gene | volume = 69 | issue = 2 | pages = 287–300 |date=September 1988 | pmid = 3148491 | doi =10.1016/0378-1119(88)90439-8 | url = http://www.dtic.mil/get-tr-doc/pdf?AD=ADA204674| archive-url = https://web.archive.org/web/20170923033835/http://www.dtic.mil/get-tr-doc/pdf?AD=ADA204674| archive-date = September 23, 2017| url-access = subscription }}</ref> LF is a Zn metalloprotease that cleaves MAPKK; EF is an adenylate cyclase that targets protein kinases. * AB5 toxins – all these toxins share a related pentameric "B" subunit, but differ in the function of their "A" part. * Ricin is expressed a single polypeptide that gets cleaved into two parts, one acting as "A" and the other acting as "B". Abrin is similar. * ''Clostridium'' neurotoxins, i.e. the tetanus toxin and the botulinum toxin, are expressed a single polypeptide that gets cleaved into two parts, one acting as "A" and the other acting as "B".

== Research ==

The two-phase mechanism of action of AB toxins is of particular interest in cancer therapy research. The general idea is to modify the B component of existing toxins to selectively bind to malignant cells. This approach combines results from cancer immunotherapy with the high toxicity of AB toxins, giving raise to a new class of chimeric protein drugs, called immunotoxins.<ref name="pmid28788054">{{cite journal |vauthors=Zahaf N, Schmidt G |date=2017-07-18 |title=Bacterial Toxins for Cancer Therapy |journal=Toxins (Basel) |volume=9 |issue=8 |page=236 |doi=10.3390/toxins9080236 |pmc=5577570 |pmid=28788054 |doi-access=free }}</ref>

==See also== *Toxalbumin *Perivitellin-2

==References== {{Reflist}}

{{DEFAULTSORT:Ab Toxin}} Category:Bacterial toxins Category:Protein families