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Structure and function of mannan-binding proteins isolated from human liver and serum
H Kurata1, T Sannoh, Y Kozutsumi
1Department of Biological Chemistry, Faculty of Pharmaceutical Sciences, Kyoto University.
Journal of Biochemistry
|June 1, 1994
Summary
Human liver produces two forms of mannan-binding proteins (MBPs): liver MBP (L-MBP) and serum MBP (S-MBP). S-MBP activates complement, while L-MBP does not, indicating post-translational modification in the liver.
Area of Science:
- Immunology
- Biochemistry
- Molecular Biology
Background:
- Mannan-binding proteins (MBPs) are key components of the innate immune system.
- Two MBP cDNA forms are known in rodents, but only one in humans.
- Understanding human MBP forms is crucial for innate immunity research.
Purpose of the Study:
- To purify and characterize two distinct human MBP forms from liver and serum.
- To investigate the functional differences between liver MBP (L-MBP) and serum MBP (S-MBP).
- To identify the structural basis for complement activation by human MBP.
Main Methods:
- Purification of L-MBP and S-MBP from human liver and serum.
- Amino acid sequencing and subunit analysis of purified MBPs.
- Complement activation assays and recombinant MBP expression in COS-1 cells.
Main Results:
- Identical amino acid sequences were found for L-MBP and S-MBP.
- L-MBP consists of approximately 9 subunits, while S-MBP has about 18 subunits.
- Only S-MBP activated complement; a specific N-terminal collagen-like domain sequence is essential for this function.
Conclusions:
- Human liver processes newly synthesized MBP into L-MBP and S-MBP forms post-translationally.
- The oligomeric state and specific domain sequence dictate MBP's complement-activating ability.
- These findings elucidate human MBP heterogeneity and its role in innate immunity.