Loop-contraction mutagenesis of a type 1 copper site

Area of Science:

• Biochemistry
• Protein Engineering
• Spectroscopy

Background:

• Cupredoxins are copper-containing proteins with diverse biological roles.
• Pseudoazurin and amicyanin are related cupredoxins with distinct active-site structures.
• Understanding structure-function relationships in cupredoxins is crucial for protein engineering.

Purpose of the Study:

• To investigate the structural and functional impact of introducing the amicyanin active-site loop into pseudoazurin via loop-contraction mutagenesis.
• To determine how this modification affects the spectroscopic properties and pKa of the histidine ligand.

Main Methods:

• Loop-contraction mutagenesis was employed to engineer the pseudoazurin protein.
• Spectroscopic techniques were used to analyze the properties of the mutated protein.
• The pKa of the detachable histidine ligand was measured.

Main Results:

• The loop contraction introduced the amicyanin active-site loop into pseudoazurin.
• Spectroscopic properties of the mutated cupric protein were largely unaffected, indicating structural integrity.
• A significant increase of two pH units in the pKa of the detachable His ligand was observed, matching amicyanin's value.

Conclusions:

• Loop-contraction mutagenesis is an effective strategy for modifying cupredoxin active sites.
• The active-site loop plays a key role in modulating the histidine ligand's pKa in pseudoazurin.
• This study provides insights into the structure-function relationship of cupredoxins and their metal-binding sites.