cystinerich

Cystinerich is an adjective used in biochemistry and proteomics to describe proteins, peptides, or protein domains that contain a high proportion of cystine residues or cysteine residues involved in disulfide bonds. Cystine is formed by the oxidative linkage of two cysteine residues, and the term denotes a qualitative property rather than a strict numeric threshold. Its exact meaning can vary by organism, protein family, or study context.

Proteins described as cystinerich often have multiple disulfide bonds, which contribute to structural stability, resistance to proteolysis, and specific folding patterns. This feature is common in many extracellular or secreted proteins, as well as in small cysteine-rich peptides such as defensins and knottins, where disulfide frameworks support compact, robust folds crucial for function.

In research and annotation, cystinerich may be used to flag potential structural motifs and to guide predictions of disulfide-bonding patterns. It can influence expression and purification strategies, since disulfide-rich proteins may require oxidative environments for correct folding and may pose challenges for recombinant production. The term remains descriptive and is often encountered in protein family descriptions, sequence analyses, and data curation.

See also: cystine, cysteine, disulfide bond, cystine knot, keratin.