Pathogenesis-related protein


Pathogenesis-related proteins are proteins produced in plants in the event of a pathogen attack. They are induced as part of systemic acquired resistance. Infections activate genes that produce PR proteins. Some of these proteins are antimicrobial, attacking molecules in the cell wall of a bacterium or fungus. Others may function as signals that spread “news” of the infection to nearby cells. Infections also stimulate the cross-linking of molecules in the cell wall and the deposition of lignin, responses that set up a local barricade that slows spread of the pathogen to other parts of the plant.
Salicylic acid plays a role in the resistance to pathogens by inducing the production of pathogenesis-related proteins. Many proteins found in wine are grape pathogen-related proteins. Those include thaumatin-like proteins and chitinases.
Many pathogenesis-related protein families also coincide with groups of human allergens, even though the allergy may have nothing to do with the defense function of the proteins. Grouping these proteins by their sequence features allows for finding potential allergenic proteins from sequenced plant genomes, a field of study dubbed "allergenomics".

Classification

, 17 families of PR proteins have been named:
FamilyDomain classificationProteinsFunctionsAllergens
PR-1
PR-1 a, PR-1 b, and PR-1 cAntifungal Cuc m 3 —oral allergy syndrome
PR-2β-1,3-GlucanasesCleaves β-1,3-glucans
  • Hev b 2 —contact dermatitis
  • Ole e 9 —respiratory allergy
  • Mus a 5 —oral allergy syndrome
PR-3Chitinase types I, II, IV, V, VI, and VIIEndochitinase
  • Pers a 1 —itchy eyes or nose, asthma, swelling, and so forth.
  • Mus a 2 —food allergy like swelling of lips, anaphylaxis, and so forth
    • PR-4Barwin domain chitinase I/IIAntifungal and chitinasePro-heveins: Hev b 6—contact dermatitis
    PR-5Thaumatin-likeAntifungal
  • Jun a 3, Cry j 1, and Cup a 3 —rhinitis, conjunctivitis, and asthma
  • Pru av 2, Mal d 2, Cap a 1, Act d 2, and Mus a 4 —oral allergy syndrome
    • PR-6Potato protease IProteinase inhibitor
    PR-7Tomato endoproteinase P69 Endoproteinase
    PR-8Cucumber chitinaseChitinase III
  • Hevamine —contact dermatitis.
  • Ziz m 1 —oral allergy syndrome
  • Cof a 1 —eye and airway allergy
    • PR-9Tobacco lignin-forming peroxidase Peroxidase
    PR-10Parsley "PR-1"Ribonuclease-like
    • Bet v 1 — allergic rhinoconjunctivitis and asthma
    • Pru av 1, Mal  d  1, Api g 1, and Dau c 1 —oral allergy syndrome
    • Gly m 4, Vig r 1, Cor a 1, and Cas s 1 —oral allergy syndrome
    PR-11Tobacco chitinase V Chitinase
    PR-12Radish Rs-AFP3 Plant Defensin
    PR-13Arabidopsis THI2.1 Thionin
    PR-14Lipid transfer proteinsShuttling of phospholipids and fatty acids
  • Par j 1 —rhinitis and asthma
  • Pru p 3, Mal d 3, Pru av 3, Pru ar 3, Cor a 8, Cas s 8, and Zea m 14 —oral allergy syndrome
    • PR-15Barley OxOa germin; Oxalate oxidase
    PR-16Barley OxOLP germin-like
    PR-17Tobacco NtPRp27 late blight resistance

    Identification

    As PR proteins are produced when plant tissue is stressed, various ways of stress signaling is used to "bait" the plant into expressing PR genes for identification. Useful stressors include an actual infection or simply defense signals such as salicylate and methyl jasmonate. The proteins can be identified by isolation, peptide digestion, and matching against the genomic sequences. The sequences obtained can then be checked against known PR protein families for categorization.