Crystallographic study of azurin from Pseudomonas putida

Area of Science:

• Biochemistry
• Structural Biology
• Crystallography

Background:

• Azurin is a blue copper protein from Pseudomonas putida that acts as an electron carrier.
• Understanding its structure is crucial for elucidating electron transfer mechanisms.

Purpose of the Study:

• To determine the crystal structures of azurin from Pseudomonas putida in both zinc-free and zinc-bound forms.
• To investigate the structural impact of zinc ion incorporation on azurin.

Main Methods:

• X-ray crystallography was employed to solve the structures of two crystal forms of azurin.
• Molecular replacement using the program MERLOT and the structure of Alcaligenes denitrificans azurin as a search model.

Main Results:

• Two crystal forms of azurin were obtained and their structures solved to high resolution (1.6-1.92 A).
• The copper-binding site in Pseudomonas putida azurin exhibits a distorted trigonal bipyramidal coordination, consistent with a weak fifth bond.
• Zinc ions incorporated into the crystal lattice bind to the protein without affecting the copper binding site, influencing unit-cell parameters and forming dimer chains.

Conclusions:

• The study provides high-resolution structural insights into Pseudomonas putida azurin and the effects of zinc binding.
• The observed dimer formation is a conserved feature across different azurin structures.
• Zinc ions can be incorporated into azurin crystals, altering lattice parameters and forming extended structures.