Editing Tryptophan synthase (section)

{{Short description|Class of enzymes}}
{{Infobox enzyme
| Name       = Tryptophan Synthase
| EC_number  = 4.2.1.20
| CAS_number = 9014-52-2
| GO_code    = 0004834
| image      = Tryptophan Synthase Dimer 3.png
| width      =
| caption    = ''Subunits: <span style="color:blue;">Beta Subunit</span>, <span style="color:lime;">Alpha Subunit</span> with <span style="color:orange;">PLP</span>, <span style="color:magenta;">IGP</span>''
}}

'''Tryptophan synthase''' or '''tryptophan synthetase''' is an [[enzyme]] ({{EnzExplorer|4.2.1.20}}) that catalyzes the final two steps in the biosynthesis of [[tryptophan]].<ref name="Tryptophan synthase">{{cite journal |vauthors=Dunn MF, Niks D, Ngo H, Barends TR, Schlichting I | title = Tryptophan synthase: the workings of a channeling nanomachine | journal = Trends in Biochemical Sciences | volume = 33 | issue = 6 | pages = 254–64 |date=June 2008 | pmid = 18486479 | doi = 10.1016/j.tibs.2008.04.008}}</ref><ref name="pmid2053470">{{cite book | vauthors = Miles EW | title = Advances in Enzymology and Related Areas of Molecular Biology | chapter = Structural basis for catalysis by tryptophan synthase | series = Advances in Enzymology and Related Areas of Molecular Biology | volume = 64 | pages = 93–172 | date = 1991 | pmid = 2053470 | doi = 10.1002/9780470123102.ch3 | isbn = 9780470123102 | author-link = Edith Wilson Miles }}</ref> It is commonly found in [[Eubacteria]],<ref name="Eubacteria">{{cite journal |vauthors=Jablonski P, Jablonski L, Pintado O, Sriranganathan N, Howde C | title = Tryptophan synthase: Identification of Pasteurella multocida tryptophan synthase B-subunit by antisera against strain PI059 | journal = Microbiology | volume = 142 | pages = 115–21 |date=September 1996 | pmid = 8581158 | doi = 10.1099/13500872-142-1-115| doi-access = free }}</ref> [[Archaebacteria]],<ref name="Archaebacteria">{{cite journal |vauthors=Lazcano A, Diaz-Villgomez E, Mills T, Oro J | title = On the levels of enzymatic substrate specificity: Implications for the early evolution of metabolic pathways | journal = Advances in Space Research | volume = 15 | issue = 3 | pages = 345–56 |date=March 1995 | pmid = 11539248 | doi = 10.1016/S0273-1177(99)80106-9}}</ref> [[Protista]],<ref name="Protista">{{cite journal |vauthors=Anderson I, Watkins R, Samuelson J, Spencer D, Majoros W, Grey M, Loftus B | title = Gene Discovery in the Acanthamoeba castellanii Genome | journal = Protist | volume = 156 | issue = 2 | pages = 203–14 |date=August 2005 | pmid = 16171187 | doi = 10.1016/j.protis.2005.04.001}}</ref> [[Fungi]],<ref name="Fungi">{{cite journal |vauthors=Ireland C, Peekhaus N, Lu P, Sangari R, Zhang A, Masurekar P, An Z | title = The tryptophan synthetase gene TRP1 of Nodulisporium sp.: molecular characterization and its relation to nodulisporic acid A production | journal = Appl Microbiol Biotechnol | volume = 79 | issue = 3 | pages = 451–9 |date=April 2008 | pmid = 18389234 | doi = 10.1007/s00253-008-1440-3| s2cid = 7230896 }}</ref> and [[Plantae]].<ref name="Plantae">{{cite journal | author = Sanjaya, Hsiao PY, Su RC, Ko SS, Tong CG, Yang RY, Chan MT | title = Overexpression of Arabidopsis thaliana tryptophan synthase beta 1 (AtTSB1) in Arabidopsis and tomato confers tolerance to cadmium stress | journal = Plant Cell Environ | volume = 31 | issue = 8 | pages = 1074–85 |date=April 2008 | pmid = 18419734 | doi = 10.1111/j.1365-3040.2008.01819.x| doi-access = }}</ref> However, it is absent from [[Animalia]].<ref name="Animalia">{{cite journal |vauthors=Eckert SC, Kubler E, Hoffmann B, Braus GH | title = The tryptophan synthase-encoding trpB gene of Aspergillus nidulans is regulated by the cross-pathway control system | journal = Mol Gen Genet | volume = 263 | issue = 5 | pages = 867–76 |date=June 2000 | pmid = 10905354 | doi = 10.1007/s004380000250| s2cid = 22836208 }}</ref> It is typically found as an α2β2 tetramer.<ref>{{cite journal | vauthors = Ahmed SA, Miles EW, Davies DR | title = Crystallization and preliminary X-ray crystallographic data of the tryptophan synthase alpha 2 beta 2 complex from Salmonella typhimurium | journal = The Journal of Biological Chemistry | volume = 260 | issue = 6 | pages = 3716–3718 | date = March 1985 | pmid = 3882715 | doi = 10.1016/s0021-9258(19)83682-7 | author-link2 = Edith Wilson Miles | doi-access = free }}</ref><ref>{{cite journal | vauthors = Hyde CC, Ahmed SA, Padlan EA, Miles EW, Davies DR | title = Three-dimensional structure of the tryptophan synthase alpha 2 beta 2 multienzyme complex from Salmonella typhimurium | journal = The Journal of Biological Chemistry | volume = 263 | issue = 33 | pages = 17857–17871 | date = November 1988 | pmid = 3053720 | doi = 10.1016/s0021-9258(19)77913-7 | doi-access = free }}</ref> The α subunits catalyze the reversible formation of [[indole]] and [[glyceraldehyde-3-phosphate]] (G3P) from indole-3-glycerol phosphate (IGP). The β subunits catalyze the irreversible condensation of indole and [[serine]] to form tryptophan in a [[pyridoxal phosphate]] (PLP) dependent reaction. Each α active site is connected to a β active site by a 25 Ångstrom long hydrophobic channel contained within the enzyme. This facilitates the diffusion of indole formed at α active sites directly to β active sites in a process known as [[substrate channeling]].<ref name="Overview">{{cite journal |vauthors=Raboni S, Bettati S, Mozzarelli A | title = Tryptophan synthase: a mine for enzymologists | journal = Cell Mol Life Sci | volume = 66 | issue = 14| pages = 2391–403 |date=April 2009 | pmid = 19387555 | doi = 10.1007/s00018-009-0028-0| hdl = 11381/2293687 | s2cid = 30220030 | hdl-access = free }}</ref> The active sites of tryptophan synthase are [[allosterically]] coupled.<ref name="Regulation">{{cite journal |vauthors=Fatmi MQ, Ai R, Chang CA | title = Synergistic regulation and ligand-induced conformational changes of tryptophan synthase | journal = Biochemistry | volume = 48 | issue = 41| pages = 9921–31 |date=September 2009 | pmid = 19764814 | doi = 10.1021/bi901358j}}</ref>