The structure of apo tryptophanase from Escherichia coli reveals a wide-open conformation.
The crystal structure of apo tryptophanase from Escherichia coli (space group F222, unit-cell parameters a = 118.4, b = 120.1, c = 171.2 A) was determined at 1.9 A resolution using the molecular-replacement method and refined to an R factor of 20.3% (R(free) = 23.2%). The structure revealed a significant shift in the relative orientation of the domains compared with both the holo form of Proteus vulgaris tryptophanase and with another crystal structure of apo E. coli tryptophanase, reflecting the internal flexibility of the molecule. Domain shifts were previously observed in tryptophanase and in the closely related enzyme tyrosine phenol-lyase, with the holo form found in an open conformation and the apo form in either an open or a closed conformation. Here, a wide-open conformation of the apo form of tryptophanase is reported. A conformational change is also observed in loop 297-303. The structure contains a hydrated Mg(2+) at the cation-binding site and a Cl(-) ion at the subunit interface. The enzyme activity depends on the nature of the bound cation, with smaller ions serving as inhibitors. It is hypothesized that this effect arises from variations of the coordination geometry of the bound cation.
Tsesin
Natalia
N
Department of Chemistry, Ben-Gurion University of the Negev, POB 653, Beer-Sheva 84105, Israel.
Kogan
Anna
A
Gdalevsky
Garik Y
GY
Himanen
Juha Pekka
JP
Cohen-Luria
Rivka
R
Parola
Abraham H
AH
Goldgur
Yehuda
Y
Almog
Orna
O
D001665:Binding Sites; D002384:Catalysis; D003460:Crystallization; D018360:Crystallography, X-Ray / Q000379:methods*; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011514:Proteus vulgaris / Q000201:enzymology; D013379:Substrate Specificity; D014368:Tryptophanase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
D029968:Escherichia coli Proteins; D014368:Tryptophanase