These cysteines either cross-link to form disulphide bonds, or bind metal ions by chelation, stabilising the protein's tertiary structure.
[1][2][3] CRPs include a highly conserved secretion peptide signal at the N-terminus and a cysteine-rich region at the C-terminus.
Defensins, a major class of CRP with an eight-cysteine motif forming four disulfide bridges,[9] are involved in pathogen response.
[4] Other putative antimicrobial CRPs include lipid transfer proteins, thionins, knottins, heveins, and snakins.
[9] In plant reproduction, CRPs are involved in pollen tube growth and guidance[10] and early embryo patterning,[11] in addition to other functions.