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[Modification of tryptophan residues in immunoglobulin M by 2-hydroxy-5-nitrobenzyl bromide]
Abstract:
The modification of tryptophan residues in monoclonal immunoglobulin M (IgM) by 2-hydroxy-5-nitrobenzyl bromide (RK) was studied at pH 2.0-2.85 and 7.0 and a RK to tryptophan molar ratio (K) from 1 to 40. At pH 2.85, the number of RK residues bound to IgM (N) in account to one HL-fragments does not exceed 10 (the HL-fragment of IgM contains 14 tryptophan residues); the plot of N vs K reaches a plateau at K greater than 20. When the pH is lowered to approximately 2, N rises to approximately 15, but the plateau is not reached. At pH 7.0, the modified IgM with N greater than 1 gives a sediment, while the product with N approximately equal to 1 remains in solution. Evidently, the latter contains the most accessible tryptophan residue (calculated per one HL-fragment). This residue was found to be one of the three residues localized in the C mu 2-domain and the adjoining N-terminal part. The possibility of multiple modification of tryptophan residues during the RK interaction with IgM in acid medium at high values of K is discussed.
Insights
Monoclonal immunoglobulin M (IgM) modification by 2-hydroxy-5-nitrobenzyl bromide (RK) reveals pH-dependent tryptophan accessibility. Lowering pH increases RK modification, suggesting conformational changes in IgM structure.
Area of Science:
- Biochemistry
- Immunology
Context:
- Monoclonal immunoglobulin M (IgM) is a crucial antibody in the immune system.
- Understanding the structural dynamics and modification sites of IgM is vital for its functional characterization.
Purpose:
- To investigate the modification of tryptophan residues in monoclonal immunoglobulin M (IgM) using 2-hydroxy-5-nitrobenzyl bromide (RK).
- To determine the effect of pH and reagent concentration on the extent and location of tryptophan modification in IgM.
Summary:
- Tryptophan modification of IgM by RK was studied across different pH values (2.0-2.85 and 7.0) and molar ratios (K=1-40).
- At pH 2.85, modification (N) plateaued around K=20, with N not exceeding 10 per HL-fragment (14 Trp residues).
- At pH ~2, N increased to ~15, without reaching a plateau.
- At pH 7.0, modified IgM with N>1 sedimented, while N≈1 remained soluble, indicating a highly accessible tryptophan residue in the latter, likely in the Cμ2-domain.
Impact:
- Identifies specific tryptophan residues in IgM that are accessible under varying pH conditions.
- Provides insights into the structural flexibility and domain-specific reactivity of IgM.
- Contributes to a deeper understanding of IgM structure-function relationships and potential modification sites.