The four cysteines ring motif in proteins

Area of Science:

• Protein structure and bioinformatics
• Structural biology
• Biochemistry

Background:

• Disulfide bonds are crucial for protein structure and function.
• Highly specialized and rare structural motifs are key to understanding protein diversity.
• The Protein Data Bank (PDB) is a comprehensive resource for protein structural information.

Purpose of the Study:

• To identify and characterize the occurrence of a specific rare motif involving four cysteines forming a 16-atom ring (4CR) with two disulfide bonds.
• To investigate the structural context and potential functional implications of the 4CR motif in proteins and peptides.

Main Methods:

• Bioinformatic search of the entire Protein Data Bank (PDB) for the 4CR motif.
• Analysis of crystallographic data to examine the 4CR motif in protein structures.
• Comparative analysis of the 4CR motif in proteins (crystallography) and peptides (NMR).

Main Results:

• The four cysteines ring (4CR) motif, featuring two disulfide bonds, was found to be extremely rare in the PDB.
• In crystallographic entries, the 4CR motif predominantly appeared in dimeric proteins, forming inter-chain covalent links.
• In a peptide studied by NMR, the 4CR moiety comprised residues from a single polypeptide chain.

Conclusions:

• The 4CR motif is a highly rare structural feature in proteins.
• Its occurrence, either linking different polypeptide chains or within a single chain, suggests a role in specialized protein functions.
• Further research is warranted to fully elucidate the functional significance of this rare motif.