|Gene:||trpA||Accession Numbers: EG11024 (EcoCyc), b1260, ECK1254|
Synonyms: try, tryp, α subunit, TSase α, A protein
Component of: tryptophan synthase (summary available)
The TrpA polypeptide (TSase α) functions as the α subunit of the tetrameric (α2-β2) tryptophan synthase complex [Miles77]. As a purified protein, the α subunit is a monomer. TSase α contains the binding site for indole-3-glycerol-phosphate (InGP) and can carry out the cleavage reaction of InGP to indole and glyceraldehyde-3-phosphate, also termed the α reaction. Within the physiological complex with the β subunit, the reaction rate is increased by 1-2 orders of magnitude (in [Kirschner91]).
TrpA has been shown to lack tryptophan residues [Henning62]. Numerous TrpA mutant studies have examined structure-function relationships in this protein. Mutations that affect catalytic activity [Hiraga96, Sarker95, Lim91, Milton86, Yutani87, Yee96, Yanofsky93, Lim91a], subunit interactions [Swift92, Lim91a], conformational stability [Hiraga96a, Lim92] and folding [Kim01d, Lim91a] have been identified.
The crystal structure of the wild-type TrpA protein has been reported at 2.8 Å resolution [Jeong04, Jeong04a], 2.5 Å resolution [Jeong05] and 2.3 Å resolution [Nishio05]. The crystal structure of a double mutant TrpA protein has been reported at 1.8 Å resolution [Jeong04a, Jeong05].
The TrpA protein has been structurally classified as a (beta alpha)(8) TIM barrel protein, a member of the common TIM barrel superfamily. Nuclear magnetic resonance spectroscopic techniques have been used to investigate its equilibrium folding mechanism in order to obtain insights into the development of structure and stability [Vadrevu08]. Many previous studies of the folding mechanism of recombinant wild-type and mutant TrpA proteins using various biophysical techniques identified intermediates in the folding pathway, for example [Beasty86, Choi95, Gualfetti99, Jeong03, Wintrode05, Wu05b, Wu07a].
|Map Position: [1,314,440 <- 1,315,246] (28.33 centisomes, 102°)||Length: 807 bp / 268 aa|
Molecular Weight of Polypeptide: 28.724 kD (from nucleotide sequence), 30.0 kD (experimental) [Gschwind79 ]
Unification Links: ASAP:ABE-0004232 , CGSC:74 , DIP:DIP-35957N , DisProt:DP00252 , EchoBASE:EB1017 , EcoGene:EG11024 , EcoliWiki:b1260 , ModBase:P0A877 , OU-Microarray:b1260 , PortEco:trpA , PR:PRO_000024117 , Pride:P0A877 , Protein Model Portal:P0A877 , RefSeq:NP_415776 , RegulonDB:EG11024 , SMR:P0A877 , String:511145.b1260 , UniProt:P0A877
Relationship Links: InterPro:IN-FAMILY:IPR002028 , InterPro:IN-FAMILY:IPR011060 , InterPro:IN-FAMILY:IPR013785 , InterPro:IN-FAMILY:IPR018204 , PDB:Structure:1V7Y , PDB:Structure:1WQ5 , PDB:Structure:1XC4 , PDB:Structure:1XCF , Pfam:IN-FAMILY:PF00290 , Prosite:IN-FAMILY:PS00167
|Biological Process:||GO:0000162 - tryptophan biosynthetic process
[UniProtGOA12, UniProtGOA11a, GOA06, Yanofsky93]
GO:0009073 - aromatic amino acid family biosynthetic process [UniProtGOA11a, Yanofsky93]
GO:0006568 - tryptophan metabolic process [GOA01a]
GO:0008152 - metabolic process [GOA01a]
GO:0008652 - cellular amino acid biosynthetic process [UniProtGOA11a]
|Molecular Function:||GO:0016829 - lyase activity
GO:0003824 - catalytic activity [GOA01a]
GO:0004834 - tryptophan synthase activity [GOA06, GOA01, GOA01a]
GO:0030170 - pyridoxal phosphate binding [Gaudet10]
|Cellular Component:||GO:0005737 - cytoplasm
GO:0005829 - cytosol [DiazMejia09, Ishihama08, LopezCampistrou05]
|MultiFun Terms:||metabolism → biosynthesis of building blocks → amino acids → tryptophan|
|Growth Medium||Growth?||T (°C)||O2||pH||Osm/L||Growth Observations|
|LB enriched||Yes||37||Aerobic||6.95||Yes [Gerdes03, Comment 1]|
|LB Lennox||Yes||37||Aerobic||7||Yes [Baba06, Comment 2]|
|M9 medium with 0.4% glucose||No||37||Aerobic||7.2||0.27||No [Patrick07, Comment 3]|
|M9 medium with 1% glycerol||No||37||Aerobic||7.2||0.35||No [Joyce06]|
|MOPS medium with 0.4% glucose||Indeterminate||37||Aerobic||7.2||0.22||Yes [Baba06, Comment 2] |
No [Feist07, Comment 4]
Enzymatic reaction of: indoleglycerol phosphate aldolase (tryptophan synthase, α subunit)
EC Number: 22.214.171.124
The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction of enzyme catalysis.
This reaction is reversible. [Yutani87]
This partial reaction catalyzed by the α subunit alone is reversible, while the overall physiological reaction catalyzed by the α2β2 tryptophan synthase complex is not (in [Lane91]).
The reverse partial reaction (indoleglycerol phosphate synthesis) catalyzed by either the α2β2 complex [Weischet76], or the α subunit [Weischet76a], has been subjected to steady-state kinetic analysis to define the reaction mechanism.
Subunit of: tryptophan synthase
Subunit composition of
tryptophan synthase = [TrpA]2[(TrpB)2]
tryptophan synthase, α subunit = TrpA (extended summary available)
tryptophan synthase, β subunit dimer = (TrpB)2 (extended summary available)
tryptophan synthase, β subunit = TrpB
The physiologically active form of tryptophan synthase is a tetrameric α2-β2 complex consisting of two α subunits (the protein product of the trpA gene) and a dimer of two β subunits (the protein product of the trpB gene). This complex catalyzes the last two steps in the biosynthesis of tryptophan [Lane91].
Although the α2-β2 complex from Escherichia coli has been well studied, the purified α2-β2 complex from Salmonella enterica subsp. enterica serovar Typhimurium (Salmonella typhimurium) provided crystals suitable for X-ray crystallography. Thus, the complex from this species has been studied in greater detail (reviewed in [Miles01, Dunn08]).
Molecular Weight: 146.5 kD (experimental) [Adachi74]
Enzymatic reaction of: tryptophan synthase
Synonyms: tryptophan desmolase, tryptophan synthetase
EC Number: 126.96.36.199
The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction of enzyme catalysis.
The reaction is irreversible in the direction shown. [Kirschner91]
The overall tryptophan synthase reaction consists of a sequence of two partial reactions. The α subunit of the complex carries out the aldol cleavage of indole-3-glycerol phosphate to indole + glyceraldehyde-3-phosphate. The β subunit is responsible for the synthesis of L-tryptophan from indole + L-serine. The α2-β2 complex, which alone catalyzes the overall reaction, proceeds at two independent α/β sites via catalysis of the α reaction on the α subunit component, channeling the product (indole) to the pyridoxal 5'-phosphate site on the β component, where, in the presence of L-serine, it is converted to tryptophan [Lane83, Dunn90] and reviewed in [Miles99]. Indole does not appear in solution and is not a free intermediate [Crawford58]. There is apparent subunit communication mediated by transduced conformational changes between the subunits, whereby the rates of the α and β reactions are strongly enhanced by, respectively, the β and α subunits [Lim91a, Kirschner91].
The partial reaction catalyzed by the α subunit is reversible [Yutani87], whereas the partial reaction catalyzed by the β subunit and the overall reaction catalyzed by the α2-β2 complex are considered to be practically irreversible (in [Kirschner91]).
Cofactor Binding Comment: Pyridoxal phosphate derivatives are much more strongly bound to the complex than to the beta subunit. This finding indicates that strong binding forces, in addition to the Schiff base linkage, exist in the complex, but not in the beta subunit. When this bond is broken during the formation of a derivative, the derivative is only weakly bound to the beta subunit, but is stongly bound to the complex by additional forces.[Miles77]
|Extrinsic-Sequence-Variant||209 -> 224|
10/20/97 Gene b1260 from Blattner lab Genbank (v. M52) entry merged into EcoCyc gene EG11024; confirmed by SwissProt match.
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