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Biosynthesis of gp160, the major trypsin-sensitive surface glycoprotein of macrophages
Abstract:
The biosynthetic origin was investigated of gp160, the trypsin- and plasmin-sensitive surface glycoprotein of caseinate-elicited macrophages from guinea pigs. Biosynthesized surface components were analyzed by reacting [35S]methionine-labeled macrophages with trinitrobenzene sulfonic acid and purifying trinitrophenyl-substituted surface proteins by immunoprecipitation. Identification of gp160 was based on its molecular weight and unique trypsin sensitivity. In addition, [35S]methionine-labeled surface and intracellular glycoproteins were purified by Lens culinaris lectin affinity chromatography. Both purification procedures demonstrated that gp160 is biosynthesized by elicited macrophages in culture. gp160 was first detected on the cell surface 60-80 min after pulse labeling; transit to the cell surface was almost maximal at 3 h. No evidence was found for intracellular accumulation of mature gp160, i.e. in time course experiments all [35S]methionine-labeled gp160 was sensitive to trypsin treatment of intact cells. However, [35S]methionine-labeled gp160 was not detected in pulse-labeled macrophages until 60 min of nonradioactive chase incubation, indicating the existence of a precursor form.
Insights
Guinea pig macrophages biosynthesize gp160, a surface glycoprotein. This protein appears on the cell surface within 3 hours, with a precursor form detected earlier.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Macrophages play a crucial role in immune responses.
- Surface glycoproteins are essential for cell-cell interactions and signaling.
- Understanding glycoprotein biosynthesis provides insights into cellular function.
Purpose of the Study:
- To investigate the biosynthetic origin of gp160, a specific surface glycoprotein found on guinea pig macrophages.
- To determine the timeline of gp160 synthesis and its transport to the cell surface.
Main Methods:
- Macrophages were labeled with [35S]methionine to track newly synthesized proteins.
- Surface proteins were identified using trinitrobenzene sulfonic acid and immunoprecipitation.
- Lens culinaris lectin affinity chromatography was used to purify glycoproteins.
- Time-course experiments were conducted to analyze protein synthesis and transport.
Main Results:
- gp160 is biosynthesized by caseinate-elicited guinea pig macrophages in culture.
- gp160 was detected on the cell surface 60-80 minutes after labeling, with maximal surface expression by 3 hours.
- No intracellular accumulation of mature gp160 was observed.
- A precursor form of gp160 was identified, indicating a post-translational modification process.
Conclusions:
- gp160 is a newly synthesized glycoprotein by guinea pig macrophages.
- The study elucidates the synthesis and cell surface trafficking pathway of gp160.
- The findings contribute to understanding macrophage surface protein dynamics and immune function.