Conformationally constrained sequence designs to bias monomer-dimer equilibriums in TASP systems

Area of Science:

• Protein engineering
• Biophysical chemistry
• Synthetic biology

Background:

• Template-assembled synthetic proteins (TASPs) offer a platform for designing novel protein structures.
• Controlling the oligomeric state (monomer vs. dimer) is crucial for protein function.
• Cavitein Q4 naturally exists as an equilibrium between monomeric and dimeric forms.

Purpose of the Study:

• To engineer cavitein Q4 variants with stabilized monomeric or dimeric structures.
• To investigate the role of histidine metal ion chelation and disulfide bonds in protein stabilization.
• To control protein quaternary structure through rational design.

Main Methods:

• Site-directed mutagenesis to introduce histidine or cysteine residues.
• Spectroscopic techniques to analyze protein oligomeric state.
• Metal ion titration to assess binding and structural effects.

Main Results:

• Mutant Q4-E3H showed increased dimerization, further enhanced by nickel ions.
• Mutant Q4-H favored a monomeric state in the presence of nickel ions.
• Disulfide mutant Q4-C2 yielded two products, but both existed as monomers.

Conclusions:

• Rational design can effectively stabilize specific oligomeric states of TASPs.
• Histidine metal ion chelation provides a tunable mechanism for controlling protein assembly.
• Disulfide bond formation can be complex, potentially occurring at multiple sites.