Loop-contraction mutagenesis of type 1 copper sites

Area of Science:

• Biochemistry
• Bioinorganic Chemistry
• Protein Engineering

Background:

• Type 1 copper proteins, such as cupredoxins, are vital electron transfer agents.
• The active site structure, particularly the copper-binding loop, influences protein function.
• Understanding structure-function relationships is key to designing novel metalloproteins.

Purpose of the Study:

• To investigate the impact of loop contraction on type 1 copper centers within cupredoxin scaffolds.
• To explore how shortening the amicyanin loop affects copper site properties and redox activity.
• To elucidate the role of loop length in tuning protein electrochemistry and electron transfer.

Main Methods:

• Introducing the shortest known type 1 copper binding loop (amicyanin) into different cupredoxin beta-barrel scaffolds.
• Characterizing the resulting loop-contraction variants using spectroscopic and electrochemical techniques.
• Analyzing structural changes and their correlation with altered functional properties.

Main Results:

• Loop contraction yielded functional type 1 copper sites with authentic properties in all variants.
• Histidine pK(a) values increased, approaching that of amicyanin, indicating loop length tunes this parameter.
• Reduction potentials decreased slightly, and electron self-exchange rates showed varied responses depending on the scaffold.
• Loop contraction favored a Cu(II) active site environment.

Conclusions:

• The length of the copper-binding loop is a critical determinant of type 1 copper center properties, including histidine pK(a) and entatic character.
• Loop contraction fine-tunes redox potentials and influences electron transfer rates, with scaffold-specific effects.
• Protein engineering via loop modification offers a route to modulate metalloprotein function.