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The novel fibronectin-binding motif and key residues of mycobacteria
M Naito1, N Ohara, S Matsumoto
1Department of Oral Bacteriology, Nagasaki University School of Dentistry, 1-7-1 Sakamoto, Nagasaki 852, Japan. mnaito@net.nagasaki-u.ac.jp
Abstract:
The binding motifs of the immunodominant antigen (Ag) alpha-Ag (Ag 85 complex B) of Mycobacterium kansasii for human fibronectin were examined using digested fragments. We defined two fibronectin-binding epitopes on 27 amino acids from 84 to 110 and on 20 amino acids from 211 to 230. The epitopes were almost conserved in the closely related Ag 85 complex of other mycobacteria species. Inhibition of fibronectin binding to intact alpha-Ag molecules was observed with peptide-(84-110), but not with peptide-(211-230). Peptide-(84-110) could also inhibit fibronectin binding to all components of the Ag 85 complex of Bacillus Calmette-Guérin (Ag 85A, Ag 85B, and Ag 85C). Further study with synthetic peptides defined 11 residues from 98 to 108 as the minimum motif. Six residues (98FEWYYQ103) were critical for interacting with fibronectin. The motif revealed no homology to other known prokaryotic and eukaryotic fibronectin-binding proteins. The defined motif of alpha-Ag is novel and unique for mycobacteria.
Insights
Researchers identified novel fibronectin-binding motifs in Mycobacterium kansasii's alpha-antigen (Ag 85 complex B). A key 11-residue sequence (98FEWYYQ103) is critical for binding, offering unique insights into mycobacterial interactions.
Area of Science:
- Microbiology
- Immunology
- Protein Chemistry
Background:
- Mycobacterium kansasii possesses an immunodominant antigen, alpha-antigen (Ag 85 complex B), crucial for host interactions.
- Fibronectin is a key extracellular matrix protein involved in cell adhesion and immune responses.
Purpose of the Study:
- To identify and characterize the fibronectin-binding motifs of Mycobacterium kansasii's alpha-antigen.
- To investigate the conservation and functional significance of these binding sites.
Main Methods:
- Peptide mapping using digested fragments of alpha-antigen.
- Inhibition assays to assess fibronectin binding.
- Synthetic peptide analysis to define minimal binding motifs.
Main Results:
- Two fibronectin-binding epitopes were identified: residues 84-110 and 211-230.
- Peptide (84-110) inhibited fibronectin binding to alpha-Ag and other Ag 85 complex components.
- A minimal 11-residue motif (98-108) with a critical 6-residue core (98FEWYYQ103) was defined.
- This motif showed no homology to known fibronectin-binding proteins, indicating novelty.
Conclusions:
- The alpha-antigen of Mycobacterium kansasii possesses unique fibronectin-binding motifs.
- The identified motif (98FEWYYQ103) is essential for fibronectin interaction and is conserved across related mycobacteria.
- This novel binding mechanism offers potential targets for therapeutic interventions.