Two-fold repeated (betaalpha)4 half-barrels may provide a molecular tool for dual substrate specificity

Area of Science:

• Biochemistry
• Structural Biology
• Microbial Genomics

Background:

• Bacterial genomes sometimes lack complete sets of genes for essential enzymes like phosphoribosyl isomerases.
• This raises questions about how these organisms maintain critical metabolic pathways with incomplete gene repertoires.

Purpose of the Study:

• To investigate the molecular basis for dual substrate specificity in the bifunctional enzyme PriA from Streptomyces coelicolor.
• To understand how organisms with reduced genomes maintain essential biological functions.

Main Methods:

• Determined the crystal structure of the bifunctional enzyme PriA using X-ray crystallography at 1.8 A resolution.
• Analyzed the enzyme's (betaalpha)(8)-barrel fold and active site architecture.
• Developed a model for substrate binding and catalysis.

Main Results:

• The crystal structure revealed a (betaalpha)(8)-barrel fold composed of two symmetric (betaalpha)(4) half-barrels.
• The active site architecture supports the catalysis of isomerization reactions for two distinct substrates.
• A model was proposed for the binding of a smaller substrate in two different orientations.

Conclusions:

• Symmetry-related half-barrels in PriA offer a molecular strategy for achieving dual substrate specificity.
• This finding expands the 'half-barrel ancestor' concept in enzyme evolution.
• The results provide insights into maintaining metabolic pathway functionality in bacteria with miniature genomes.