Evolutionary relationships among gamma-carboxymuconolactone decarboxylases

Area of Science:

• Biochemistry
• Enzymology
• Microbial Biochemistry

Background:

• gamma-Carboxymuconolactone decarboxylase (EC 4.1.1.44) is a key enzyme in aromatic compound metabolism.
• Comparative studies of this enzyme across different bacterial species can reveal evolutionary relationships and functional conservation.

Purpose of the Study:

• To compare the biochemical and immunological properties of gamma-Carboxymuconolactone decarboxylase from Azotobacter vinelandii with those from Acinetobacter calcoaceticus and Pseudomonas putida.
• To investigate the structural similarities and differences between these isofunctional enzymes.

Main Methods:

• Enzyme purification and characterization.
• Hexamers formation analysis.
• Immunological cross-reactivity assays.
• NH2-terminal amino acid sequencing.

Main Results:

• All three decarboxylases are hexamers composed of identical subunits (~13,300 daltons).
• Azotobacter vinelandii and Pseudomonas putida decarboxylases exhibit immunological cross-reactivity and highly similar NH2-terminal amino acid sequences (≤7 differences in 36 residues).
• Acinetobacter calcoaceticus decarboxylase shows no immunological cross-reactivity and approximately 50% divergence in NH2-terminal amino acid sequence compared to the other two.

Conclusions:

• The gamma-Carboxymuconolactone decarboxylases from A. vinelandii and P. putida are closely related, suggesting recent evolutionary divergence or horizontal gene transfer.
• The A. calcoaceticus decarboxylase represents a more distantly related or independently evolved enzyme, highlighting diversity in aromatic catabolic pathways.