How do haloarchaea synthesize aromatic amino acids?

Area of Science:

• Microbiology
• Biochemistry
• Genomics

Background:

• Aromatic amino acid (AroAA) biosynthesis is essential for life.
• The de novo pathway for AroAA in Halobacterium salinarum was previously uncharacterized.
• Comparison with Methanocaldococcus jannaschii suggested a non-classical pathway initiation.

Purpose of the Study:

• To elucidate the de novo aromatic amino acid biosynthesis pathway in H. salinarum.
• To identify and characterize the genes and proteins involved in the initial steps of this pathway.
• To validate the proposed pathway using biochemical and genetic approaches.

Main Methods:

• Genomic analysis to predict gene functions.
• Biochemical assays to determine enzyme activities.
• Genetic manipulation (mutant generation) to study pathway function.
• Nutritional requirement and uptake studies.
• DNA microarray analysis to assess gene expression.

Main Results:

• Identified OE1472F and OE1475F as key genes encoding enzymes for the initial steps, producing 3-dehydroquinate (DHQ).
• Confirmed that the pathway converges with the canonical route at dehydroshikimate (DHS) production, catalyzed by OE1477R.
• Demonstrated differential expression of canonical pathway genes when H. salinarum is deprived of AroAA, indicating pathway utilization.
• Nutritional and uptake studies supported the proposed roles of the identified genes.

Conclusions:

• H. salinarum initiates aromatic amino acid biosynthesis via a non-classical pathway involving OE1472F and OE1475F.
• The pathway integrates with the canonical route for subsequent steps.
• The canonical pathway genes are actively utilized and regulated in response to nutrient availability.