Subsystem: Common Pathway For Synthesis of Aromatic Compounds (DAHP synthase to chorismate)
This subsystem's description is:
The common pathway for aromatic biosynthetic compounds starts with 2-keto-3-deoxy-D-arabino- heptulosonate-7-phosphate synthase (DAHP synthase) and proceeds through 7 more steps to the major intermediate, chorismate. Cohesion groups have been determined for each protein of the common pathway. See publication, Bonner et al., Cohesion group approach for evolutionary analysis of TyrA, a protein family with wide-rangeing substrate specificities, MMBR72:13-53, 2008 for cohesion group analysis.
There are 3 types of DAHP synthase, the first step of the pathway: DAHP synthase I alpha and DAHP synthase I beta are homologous proteins (AroAI alpha and AroAI beta), and DAHP synthase II which is not homologous with the two AroAI proteins (AroAII.) The second step is 3-dehydroquinate synthase (AroB). The third step has are two nonhomologous types of 3-dehydroquinate dehydratase, (AroCI and AroCII). An alternative route feeds into the aromatic pathway at the intermediate, 3-dehydroquinate. These enzymes includes 2-amino-3,7-dideoxy-D-threo-hept-6-ulosonate synthase (AroA')and 3,7-dideoxy-D-threo-hepto-2,6-diulosonate synthase (AroB'). 2-Keto-3-deoxy-D-manno-octulosonate-8-phosphate synthase (KdsA) which is often mistaken for DAHP synthase is included as an auxiliary protein in this subsystem.
Shikimate dehydrogenase the fifth step, is subdivided into four homologous groups (AroDI alpha, beta, gamma, delta) based on literature and phylogenetic trees. The sixth step, shikimate kinase falls into two nonhomoloogous groups, AroEI and AroEII (archaea). 5-Enolpyruvylshikimate-3-phosphate synthase (EPSPS)(AroF), the sixth step, is followed by chorismate synthase (AroG).
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