Kinetics of binding of LPS to recombinant CD14, TLR4, and MD-2 proteins

Area of Science:

• Immunology
• Molecular Biology
• Biochemistry

Background:

• Toll-like receptor 4 (TLR4), CD14, and MD-2 form a pattern recognition receptor complex crucial for the innate immune response to Gram-negative bacteria.
• This complex initiates the immune cascade upon detecting lipopolysaccharide (LPS), a key component of bacterial outer membranes.

Purpose of the Study:

• To investigate the binding kinetics of LPS to recombinant CD14, MD-2, and TLR4 proteins.
• To determine the affinity and interaction rates between LPS and its coreceptors, CD14 and MD-2.

Main Methods:

• Surface Plasmon Resonance (SPR) technique was utilized to measure real-time binding interactions.
• Recombinant CD14, MD-2, and TLR4 proteins were produced in insect cells and immobilized for binding assays.
• Kinetic parameters, including association rate constant (Kon), dissociation rate constant (Koff), and dissociation constant (KD), were determined.

Main Results:

• The dissociation constant (KD) for LPS binding to immobilized CD14 was 8.7 µM.
• The dissociation constant (KD) for LPS binding to immobilized MD-2 was 2.3 µM.
• LPS demonstrated slow association (Kon = 5.61 x 10^3 M⁻¹S⁻¹) and fast dissociation (Koff = 1.28 x 10² S⁻¹) with MD-2, yielding an affinity constant (KD) of 2.33 x 10⁻⁶ M at 25°C.

Conclusions:

• The determined binding affinities of LPS to CD14 and MD-2 are consistent with their established roles in innate immunity.
• CD14 likely facilitates the transfer of LPS to the TLR4/MD-2 complex, initiating downstream signaling pathways.
• These findings provide quantitative insights into the molecular interactions governing the initial steps of Gram-negative bacterial recognition.