n→π* Interactions Modulate the Properties of Cysteine Residues and Disulfide Bonds in Proteins

J Am Chem Soc. 2018 Dec 19;140(50):17606-17611. doi: 10.1021/jacs.8b09701. Epub 2018 Dec 6.


Noncovalent interactions are ubiquitous in biology, taking on roles that include stabilizing the conformation of and assembling biomolecules, and providing an optimal environment for enzymatic catalysis. Here, we describe a noncovalent interaction that engages the sulfur atoms of cysteine residues and disulfide bonds in proteins-their donation of electron density into an antibonding orbital of proximal amide carbonyl groups. This n→ π* interaction tunes the reactivity of the CXXC motif, which is the critical feature of thioredoxin and other enzymes involved in redox homeostasis. In particular, an n→ π* interaction lowers the p Ka value of the N-terminal cysteine residue of the motif, which is the nucleophile that initiates catalysis. In addition, the interplay between disulfide n→ π* interactions and C5 hydrogen bonds leads to hyperstable β-strands. Finally, n→ π* interactions stabilize vicinal disulfide bonds, which are naturally diverse in function. These previously unappreciated n→ π* interactions are strong and underlie the ability of cysteine residues and disulfide bonds to engage in the structure and function of proteins.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Amino Acid Motifs
  • Animals
  • Aspergillus / enzymology
  • Bacteria / enzymology
  • Bacterial Proteins / chemistry
  • Catalytic Domain
  • Computational Biology
  • Computer Simulation
  • Cysteine / chemistry*
  • Disulfides / chemistry*
  • Drosophila melanogaster / chemistry
  • Enzymes / chemistry
  • Fungal Proteins / chemistry
  • Humans
  • Hydrogen Bonding
  • Models, Chemical
  • Protein Conformation
  • Proteins / chemistry*
  • Static Electricity


  • Bacterial Proteins
  • Disulfides
  • Enzymes
  • Fungal Proteins
  • Proteins
  • Cysteine