Dual function of novel pollen coat (surface) proteins: IgE-binding capacity and proteolytic activity disrupting the airway epithelial barrier

PLoS One. 2013;8(1):e53337. doi: 10.1371/journal.pone.0053337. Epub 2013 Jan 7.


Background: The pollen coat is the first structure of the pollen to encounter the mucosal immune system upon inhalation. Prior characterizations of pollen allergens have focused on water-soluble, cytoplasmic proteins, but have overlooked much of the extracellular pollen coat. Due to washing with organic solvents when prepared, these pollen coat proteins are typically absent from commercial standardized allergenic extracts (i.e., "de-fatted"), and, as a result, their involvement in allergy has not been explored.

Methodology/principal findings: Using a unique approach to search for pollen allergenic proteins residing in the pollen coat, we employed transmission electron microscopy (TEM) to assess the impact of organic solvents on the structural integrity of the pollen coat. TEM results indicated that de-fatting of Cynodon dactylon (Bermuda grass) pollen (BGP) by use of organic solvents altered the structural integrity of the pollen coat. The novel IgE-binding proteins of the BGP coat include a cysteine protease (CP) and endoxylanase (EXY). The full-length cDNA that encodes the novel IgE-reactive CP was cloned from floral RNA. The EXY and CP were purified to homogeneity and tested for IgE reactivity. The CP from the BGP coat increased the permeability of human airway epithelial cells, caused a clear concentration-dependent detachment of cells, and damaged their barrier integrity.

Conclusions/significance: Using an immunoproteomics approach, novel allergenic proteins of the BGP coat were identified. These proteins represent a class of novel dual-function proteins residing on the coat of the pollen grain that have IgE-binding capacity and proteolytic activity, which disrupts the integrity of the airway epithelial barrier. The identification of pollen coat allergens might explain the IgE-negative response to available skin-prick-testing proteins in patients who have positive symptoms. Further study of the role of these pollen coat proteins in allergic responses is warranted and could potentially lead to the development of improved diagnostic and therapeutic tools.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Base Sequence
  • Cell Adhesion / drug effects
  • Cell Membrane Permeability / drug effects
  • Cells, Cultured
  • Chemical Fractionation
  • Cynodon / chemistry*
  • Cynodon / immunology
  • Cynodon / ultrastructure
  • Cysteine Proteases / isolation & purification
  • Cysteine Proteases / metabolism
  • Cysteine Proteases / pharmacology*
  • Dose-Response Relationship, Drug
  • Endo-1,4-beta Xylanases / isolation & purification
  • Endo-1,4-beta Xylanases / metabolism
  • Endo-1,4-beta Xylanases / pharmacology*
  • Epithelial Cells / cytology
  • Epithelial Cells / drug effects*
  • Epithelial Cells / metabolism
  • Humans
  • Immunoglobulin E / chemistry
  • Immunoglobulin E / immunology
  • Immunoglobulin E / metabolism*
  • Microscopy, Electron, Transmission
  • Molecular Sequence Data
  • Plant Proteins / isolation & purification
  • Plant Proteins / metabolism
  • Plant Proteins / pharmacology*
  • Pollen / chemistry*
  • Pollen / immunology
  • Pollen / ultrastructure
  • Protein Binding
  • Respiratory Mucosa / cytology
  • Respiratory Mucosa / drug effects*
  • Respiratory Mucosa / metabolism
  • Rhinitis, Allergic, Seasonal / immunology
  • Solvents


  • Plant Proteins
  • Solvents
  • Immunoglobulin E
  • Endo-1,4-beta Xylanases
  • Cysteine Proteases

Grant support

The Strategic Program for Asthma Research (www.spar-aaf.org); National Science Foundation, http://www.nsf.gov/ “Arabidopsis 2010: Functional analysis of pollen exine assembly,” MCB-0520283; Department of Energy, http://energy.gov/ “Cell-Cell Interaction during Pollen Tube Guidance in Arabidopsis," DE-FG02-96ER20240; The McHugh Otolaryngology Research Fund. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.