Cysteine
Cysteine — A sulfur-containing amino acid (Cys, C) capable of forming disulfide bonds, critical for peptide tertiary structure and stability.
What Is Cysteine?
Cysteine (Cys, C) is a sulfur-containing amino acid with a thiol (-SH) side chain, molecular weight 121.16 Da. It is the most chemically reactive of the 20 standard amino acids and plays critical roles in peptide structure through disulfide bond formation, metal coordination in metallopeptides like GHK-Cu, and redox chemistry in glutathione.
Roles in Peptide Research
- Disulfide bonds: Two cysteines form S-S bridges that stabilize tertiary structure in insulin, oxytocin, somatostatin
- Bioconjugation: Maleimide-thiol reactions enable site-specific labeling and conjugation
- Metal binding: Cysteine thiolates coordinate zinc in zinc fingers and copper in metallopeptides
- Redox sensing: Thiol/disulfide switching acts as a molecular redox sensor
Synthesis Considerations
Cysteine requires side-chain protection during SPPS (Trt, Acm, or tBu groups). Free cysteine oxidizes rapidly in air. Racemization at cysteine during coupling is a known risk; use HATU with minimal base exposure.
Frequently Asked Questions
What is Cysteine?
A sulfur-containing amino acid (Cys, C) capable of forming disulfide bonds, critical for peptide tertiary structure and stability.
Why is Cysteine important in peptide research?
Cysteine is a fundamental concept in amino acid as it relates to peptide science. It directly influences experimental design, compound characterization, and the reliability of research outcomes across biochemistry and molecular biology disciplines.