Carbohydrate recognition domain of surfactant protein D mediates interactions with Pneumocystis carinii glycoprotein A

Am J Respir Cell Mol Biol. 2001 Apr;24(4):475-84. doi: 10.1165/ajrcmb.24.4.3504.

Abstract

Pneumocystis carinii continues to cause severe pneumonia in immunocompromised patients. Surfactant protein D (SP-D), a lung collectin, markedly accumulates during P. carinii pneumonia and binds to glycoprotein A (gpA) on the surface of P. carinii, thereby enhancing interactions with alveolar macrophages. Herein, we report the structural basis of the interaction of SP-D with gpA. We demonstrate that natural SP-D binds to purified gpA in the presence of 2 mM calcium in a saturable, concentration-dependent manner, which is abolished by 10 mM ethylenediaminetetraacetic acid. Increasing concentrations of calcium under otherwise cation-free conditions significantly enhance SP-D binding to gpA, whereas manganese and magnesium cations have minimal effect. Maximal SP-D binding occurs at pH 7.4, with significant inhibition at pH 4. SP-D binding to gpA is also competitively inhibited by maltose>glucose>mannose>N-acetyl-glucosamine. Comparison of the binding of various natural and recombinant forms of SP-D to gpA reveals that the number of carbohydrate recognition domains (CRDs) in a given SP-D form determines the relative extent of binding to gpA. Maximal binding is observed with natural SP-D (dodecamers and higher order SP-D complexes) followed by recombinant dodecamers. In contrast, recombinant full-length trimers exhibit substantially less binding, which is similar to that observed with a recombinant truncated molecule consisting of the CRD and neck regions, and containing trimers of this portion of the molecule. Taken together, these findings strongly indicate that the CRD of SP-D mediates interaction with P. carinii gpA through its attached oligosaccharides and that the extent of SP-D binding to P. carinii is greatest with dodecamers and higher order forms of SP-D.

Publication types

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

MeSH terms

  • Acetylglucosamine / metabolism
  • Acetylglucosamine / pharmacology
  • Animals
  • Binding Sites / physiology
  • Binding, Competitive / physiology
  • Calcium / metabolism
  • Carbohydrate Metabolism*
  • Carbohydrates / pharmacology
  • Fungal Proteins / chemistry
  • Fungal Proteins / metabolism*
  • Glucose / metabolism
  • Glucose / pharmacology
  • Glycoproteins / chemistry*
  • Glycoproteins / metabolism*
  • Hydrogen-Ion Concentration
  • Maltose / metabolism
  • Maltose / pharmacology
  • Mannose / metabolism
  • Mannose / pharmacology
  • Membrane Glycoproteins / chemistry
  • Membrane Glycoproteins / metabolism*
  • Pneumocystis*
  • Pneumonia, Pneumocystis / metabolism*
  • Protein Structure, Tertiary
  • Pulmonary Surfactant-Associated Protein D
  • Pulmonary Surfactants / chemistry*
  • Pulmonary Surfactants / metabolism*
  • Rats
  • Rats, Sprague-Dawley
  • Recombinant Proteins / genetics
  • Recombinant Proteins / pharmacology

Substances

  • Carbohydrates
  • Fungal Proteins
  • Glycoproteins
  • Membrane Glycoproteins
  • Pulmonary Surfactant-Associated Protein D
  • Pulmonary Surfactants
  • Recombinant Proteins
  • GPA protein, Pneumocystis carinii sp.
  • Maltose
  • Glucose
  • Mannose
  • Calcium
  • Acetylglucosamine