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Lactoferrin binding to lysozyme-treated Micrococcus luteus
Abstract:
When the cell lysis of Micrococcus luteus by hen egg white or human lysozyme is performed in the presence of bovine or human lactoferrin, a temporary increase of the turbidity of the solution as followed at 450 nm is observed. Examination of the suspension under light microscopy has proven that the protoplasts produced upon lysozyme action are agglutinated by lactoferrin. The rate of agglutination depends on pH, lactoferrin, lysozyme and cells concentrations. Agglutination is maximal at pH 5.5. Around 1.4 X 10(6) binding sites for lactoferrin per cell have been determined through a Scatchard plot analysis. The binding to the cells is not mediated by the glycosidic moiety of lactoferrin but rather by a charge-to charge interaction as succinylation of about four out of the 39 lysines of lactoferrin completely abolishes its ability to agglutinate the cells. Binding does not depend on ionic iron nor on the iron content of lactoferrin itself.
Insights
Lactoferrin causes Micrococcus luteus protoplasts to clump together during cell lysis. This interaction, driven by charge, is influenced by pH and protein concentrations, revealing insights into bacterial cell wall interactions.
Area of Science:
- Microbiology
- Biochemistry
- Cell Biology
Background:
- Lysozyme is crucial for bacterial cell lysis.
- Lactoferrin is a known iron-binding protein with antimicrobial properties.
- The interaction between lysozyme, lactoferrin, and bacterial cells requires further elucidation.
Purpose of the Study:
- To investigate the effect of lactoferrin on Micrococcus luteus cell lysis by lysozyme.
- To characterize the mechanism and binding kinetics of lactoferrin-induced agglutination.
Main Methods:
- Turbidity measurements at 450 nm to monitor cell lysis and agglutination.
- Light microscopy to visualize protoplast agglutination.
- Scatchard plot analysis to determine lactoferrin binding sites.
- Chemical modification (succinylation) of lactoferrin to probe binding interactions.
Main Results:
- Lactoferrin temporarily increased turbidity, indicating agglutination of lysozyme-treated Micrococcus luteus protoplasts.
- Agglutination rate was dependent on pH (maximal at 5.5), lactoferrin, lysozyme, and cell concentrations.
- Approximately 1.4 x 10^6 lactoferrin binding sites per cell were identified.
- Binding was mediated by charge-to-charge interactions, not the glycosidic moiety or iron content of lactoferrin.
Conclusions:
- Lactoferrin actively agglutinates Micrococcus luteus protoplasts generated by lysozyme.
- The interaction is primarily electrostatic, involving lysine residues on lactoferrin.
- This study clarifies a specific mechanism of lactoferrin-bacterial interaction independent of iron.