Biology:Cysteine-rich protein

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Short description: Small protein with high number of disulphide bonds

Cysteine-rich proteins (CRP, cysteine-rich peptide or disulphide-rich peptide) are small proteins that contain a large number of cysteines. 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.[4]

Structure

Example disulphide-linked CRP: a thionein. Cysteines in yellow. (PDB: 1BHP​)
Example metal binding CRP: a metallothionein bound to zinc ions. Cysteines in yellow, zinc in purple. (PDB: 1JJD​)

Disulphides

In an oxidising environment cysteines cross-link to form disulphide bonds. CRPs that form these typically have an even number of cysteines.[5]

Metal binding

Cysteines can coordinate one or more metal ions by forming a chelation complex around them.[6]

Functions in plants

CRPs are numerous in plants, with 756 CRP-encoding genes in the Arabidopsis thaliana genome.[7] Several CRPs bind known receptors,[8] but most CRP signaling mechanisms and protein interactions are uncharacterized. Characterized CRPs function as short-range intercellular signals during processes such as plant defense, bacterial symbiosis, stomatal patterning, fertilization, vegetative tissue development, and seed development.[4]

Many CRPs function in plant defense. 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. Additionally, some CRPs have allergenic, ɑ-amylase inhibitory, or protease inhibitory functions that deter herbivores.[9]

In plant reproduction, CRPs are involved in pollen tube growth and guidance[10] and early embryo patterning,[11] in addition to other functions. Among those involved in pollen tube attraction are the LUREs, a group of ovular pollen-tube attractants in Arabidopsis thaliana and Torenia fournieri[12] that preferentially attract conspecific pollen,[10] and STIG1, a CRP expressed in the stigma of Solanum lycopersicum that interacts with the pollen-specific receptor PRK2.[8] In early embryo development, CRPs such as ESF1 are necessary for suspensor development and normal seed morphology.[11]

References

  1. ↑ "Structural classification of small, disulfide-rich protein domains". Journal of Molecular Biology 359 (1): 215–37. May 2006. doi:10.1016/j.jmb.2006.03.017. PMID 16618491. 
  2. ↑ "Folding of small disulfide-rich proteins: clarifying the puzzle". Trends in Biochemical Sciences 31 (5): 292–301. May 2006. doi:10.1016/j.tibs.2006.03.005. PMID 16600598. http://ddd.uab.cat/record/67768. 
  3. ↑ Metallothioneins and related chelators. Sigel, Astrid., Sigel, Helmut., Sigel, Roland K. O.. Cambridge: Royal Society of Chemistry. 2009. ISBN 978-1-84755-953-1. OCLC 429670531. https://www.worldcat.org/oclc/429670531. 
  4. ↑ 4.0 4.1 4.2 "Cysteine-rich peptides (CRPs) mediate diverse aspects of cell-cell communication in plant reproduction and development". Journal of Experimental Botany 62 (5): 1677–86. March 2011. doi:10.1093/jxb/err002. PMID 21317212. 
  5. ↑ Lavergne, Vincent; J. Taft, Ryan; F. Alewood, Paul (2012-08-01). "Cysteine-Rich Mini-Proteins in Human Biology". Current Topics in Medicinal Chemistry 12 (14): 1514–1533. doi:10.2174/156802612802652411. ISSN 1568-0266. PMID 22827521. http://dx.doi.org/10.2174/156802612802652411. 
  6. ↑ Maret, Wolfgang (2008-05-01). "Metallothionein redox biology in the cytoprotective and cytotoxic functions of zinc" (in en). Experimental Gerontology. Zinc and Ageing (ZINCAGE Project) 43 (5): 363–369. doi:10.1016/j.exger.2007.11.005. ISSN 0531-5565. PMID 18171607. http://www.sciencedirect.com/science/article/pii/S0531556507002720. 
  7. ↑ "Active role of small peptides in Arabidopsis reproduction: Expression evidence". Journal of Integrative Plant Biology 57 (6): 518–21. June 2015. doi:10.1111/jipb.12356. PMID 25828584. 
  8. ↑ 8.0 8.1 "Tomato Pistil Factor STIG1 Promotes in Vivo Pollen Tube Growth by Binding to Phosphatidylinositol 3-Phosphate and the Extracellular Domain of the Pollen Receptor Kinase LePRK2". The Plant Cell 26 (6): 2505–2523. June 2014. doi:10.1105/tpc.114.123281. PMID 24938288. 
  9. ↑ 9.0 9.1 "Small cysteine-rich peptides resembling antimicrobial peptides have been under-predicted in plants". The Plant Journal 51 (2): 262–80. July 2007. doi:10.1111/j.1365-313X.2007.03136.x. PMID 17565583. 
  10. ↑ 10.0 10.1 "Arabidopsis". Science 364 (6443): eaau9564. May 2019. doi:10.1126/science.aau9564. PMID 31147494. 
  11. ↑ 11.0 11.1 "Central cell-derived peptides regulate early embryo patterning in flowering plants". Science 344 (6180): 168–72. April 2014. doi:10.1126/science.1243005. PMID 24723605. Bibcode: 2014Sci...344..168C. 
  12. ↑ "Peptide signaling in pollen tube guidance". Current Opinion in Plant Biology 28: 127–36. December 2015. doi:10.1016/j.pbi.2015.10.006. PMID 26580200. 



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