Selectivity in heavy metal- binding to peptides and proteins

Area of Science:

• Biochemistry
• Structural Biology
• Metalloprotein Chemistry

Background:

• Heavy metal-binding proteins utilize conserved motifs like MXCXXC for metal coordination.
• Understanding these motifs is crucial for designing biomimetic materials and therapeutics.
• The periplasmic mercury-binding protein MerP contains a well-studied MXCXXC motif.

Purpose of the Study:

• To investigate how sequence variations in the MXCXXC motif affect metal-binding affinities and structures.
• To determine the three-dimensional structures of synthetic peptides mimicking the MerP motif.
• To explore the metal-binding specificity of peptides with altered cysteine and alanine registers.

Main Methods:

• Synthesis of three 18-residue peptides with varying cysteine-alanine arrangements (CAAC, CACA, CCAA).
• Determination of metal-binding affinities using biophysical techniques.
• Solution structure determination of metal-bound peptides via Nuclear Magnetic Resonance (NMR) spectroscopy.

Main Results:

• Peptide sequence significantly influences metal specificity; vicinal cysteines (CCAA) selectively bind mercury.
• Three-dimensional structures of mercury-bound peptides, despite being linear bicoordinate complexes, showed considerable structural diversity.
• The CAAC peptide bound to Cadmium(II) revealed structural plasticity, accommodating non-linear coordination modes.

Conclusions:

• The precise arrangement of cysteines and alanines within the MXCXXC motif dictates metal-binding specificity.
• NMR-derived structures demonstrate that even similar coordination geometries can arise from distinct peptide conformations.
• The malleability of metal-binding loops allows for diverse coordination strategies, relevant for heavy metal detoxification and sensing.