Titre du document / Document title

Crystal structure of the reaction complex of 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase from Thermotoga maritima refines the catalytic mechanism and indicates a new mechanism of allosteric regulation

Auteur(s) / Author(s)

SHUMILIN Igor A. ; BAUERLE Ronald ; JING WU ; WOODARD Ronald W. ; KRETSINGER Robert H. ;

Résumé / Abstract

3-Deoxy-D-arabino-heptulosonate-7-phosphate synthase (DAHPS) catalyzes the first reaction of the aromatic biosynthetic pathway in bacteria, fungi, and plants, the condensation of phosphoenolpyruvate (PEP) and D-erythrose-4-phosphate (E4P) with the formation of DAHP. Crystals of DAHPS from Thermotoga maritima (DAHPS_Tm) were grown in the presence of PEP and metal cofactor, Cd₂₊, and then soaked with E4P at 4 °C where the catalytic activity of the enzyme is negligible. The crystal structure of the "frozen" reaction complex was determined at 2.2 A resolution. The subunit of the DAHPS_Tm homotetramer consists of an N-terminal ferredoxin-like (FL) domain and a (β/α)⁸-barrel domain. The active site located at the C-end of the barrel contains Cd₂₊, PEP, and E4P, the latter bound in a non-productive conformation. The productive conformation of E4P is suggested and a catalytic mechanism of DAHPS is proposed. The active site of DAHPS_Tm is nearly identical to the active sites of the other two known DAHPS structures from Escherichia coli (DAHPS_Ec) and Saccharomyces cerevisiae (DAHPS_Sc). However, the secondary, tertiary, and quaternary structures of DAHPS_Tm are more similar to the functionally related enzyme, 3-deoxy-D-manno-octulosonate-8-phosphate synthase (KDOPS) from E. coli and Aquiflex aeolicus, than to DAHPS_Ec and DAHPS_Sc. Although DAHPS_Tm is feedback-regulated by tyrosine and phenylalanine, it lacks the extra barrel segments that are required for feedback inhibition in DAHPS_Ec and DAHPS_Sc. A sequence similarity search revealed that DAHPSs of phylogenetic family Iβ possess a FL domain like DAHPS_Tm while those of family Iα have extra barrel segments similar to those of DAHPS_Ec and DAHPS_Sc. This indicates that the mechanism of feedback regulation in DAHPS_Tm and other family Iβ enzymes is different from that of family Iα enzymes, most likely being mediated by the FL domain.

Revue / Journal Title

Journal of molecular biology   ISSN 0022-2836   CODEN JMOBAK 

Source / Source

2004, vol. 341, n^o2, pp. 455-466 [12 page(s) (article)]

Langue / Language

Anglais

Editeur / Publisher

Elsevier, Oxford, ROYAUME-UNI  (1959) (Revue)

Localisation / Location

INIST-CNRS, Cote INIST : 9122, 35400012041191.0110