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Isolation and partial characterization of human low molecular weight protein associated with pulmonary surfactant
K Kogishi1, M Kurozumi, Y Fujita
1Department of Pathology, Chest Disease Research Institute, Kyoto University, Japan.
Abstract:
A low molecular weight (MW) protein was isolated from the bronchoalveolar lavage fluid of a patient with alveolar proteinosis. The protein was isolated on DEAE-cellulose and CM-cellulose columns by a cross-reaction with the monoclonal antibody against pig low MW protein (15 kDa) used as a marker. Acidic ethanol-soluble proteins obtained from the fractions eluted by 0.09 to 0.16 M NaCl concentration from the CM-cellulose column migrated mainly as a 15-kDa band in the SDS-PAGE system without urea but mainly as a 5-kDa band in a system with 8 M urea. The isoelectric point of the protein was pH 10 to 11, and it contained a large proportion of hydrophobic amino acids (72%), especially leucine (17%). The arginine content was also high (9%). Two monoclonal antibodies were raised against this low MW protein, and immunohistochemical studies revealed that the antigen was located in the inclusions of alveolar wall cells in normal lungs and in lungs from a patient with alveolar proteinosis. These results indicate that the low MW protein originates from lamellar inclusions of alveolar wall cells (possibly type II epithelial cells) and is secreted into alveolar spaces.
Insights
Researchers isolated a low molecular weight (MW) protein from bronchoalveolar lavage fluid of a patient with alveolar proteinosis. This protein, found in alveolar wall cell inclusions, is likely secreted into alveolar spaces.
Area of Science:
- Pulmonary Medicine
- Biochemistry
- Cell Biology
Background:
- Alveolar proteinosis is a rare lung disease characterized by the accumulation of surfactant-like material in alveoli.
- The exact origin and composition of the proteinaceous material in alveolar proteinosis remain incompletely understood.
Purpose of the Study:
- To isolate and characterize a low molecular weight (MW) protein from the bronchoalveolar lavage fluid (BALF) of a patient with alveolar proteinosis.
- To investigate the cellular origin and localization of this protein within lung tissue.
Main Methods:
- Protein isolation using ion-exchange chromatography (DEAE-cellulose and CM-cellulose).
- Protein characterization by SDS-PAGE (with and without urea), isoelectric focusing, and amino acid analysis.
- Immunohistochemical analysis using monoclonal antibodies against the isolated protein.
Main Results:
- A low MW protein (apparent MW 15 kDa without urea, 5 kDa with 8 M urea) was isolated from BALF.
- The protein exhibited an isoelectric point of pH 10-11 and was rich in hydrophobic amino acids (72%), particularly leucine.
- Immunohistochemistry revealed the protein's presence in lamellar inclusions within alveolar wall cells (potentially type II pneumocytes) in both normal and diseased lungs.
Conclusions:
- The identified low MW protein originates from lamellar inclusions within alveolar wall cells.
- This protein is likely secreted into the alveolar spaces and may play a role in the pathogenesis of alveolar proteinosis.