Reconstruction of LPS transfer cascade reveals structural determinants within LBP, CD14, and TLR4-MD2 for efficient LPS reconstruction and transfer
TLR4-MD2 plays a key role in triggering the innate immune response against Gram-negative bacterial infection. LBP and CD14 accelerate the recognition of Gram-negative bacteria LPS (endotoxin) by the TLR4-MD2 complex. Researchers at KAIST discovered dynamic molecular interactions among LPS, LBP, CD14 and TLR4-MD2 using transmission electron microscopy and fluorescence analysis on total internal reflection microscopy.
Lipopolysaccharide (LPS), also called endotoxin, is the major component of the outer membrane of Gram-negative bacteria. Binding of LPS to Toll-like receptor 4 (TLR4)-MD2 complex triggers host innate immune responses. LPS-binding protein (LBP) and CD14 make this transfer of LPS to TLR4-MD2 as efficient as possible, increasing the sensitivity of LPS detection. However, severe bacterial infection and a sudden increase of LPS in the serum can cause inappropriate amplification of the immune response, resulting in sepsis.
The sequence and dynamics of the interactions of these proteins and LPS are not well understood.
We characterized the dynamic intermediates (i.e., LPS-bound LBP, LPS-bound CD14, CD14-LBP-LPS complex, and the CD14-LPS-TLR4-MD2 complex) within the entire LPS transfer process. Importantly, this was done at the single-molecule, or event resolution, level using electron microscopy and fluorescence analysis on a total internal reflection (TIRF) microscopy. A single LBP molecule bound longitudinally to the surface of LPS micelles was able to catalyze multiple rounds of LPS transfer to CD14 via the key charged functional motif within LBP and CD14. Then, CD14 delivered an LPS molecule to MD2 in a TLR4-dependent manner, particularly the LRR13-LRR15 domain in TLR4. These discoveries provide important mechanistic insights into the recognition of LPS by LBP and the entire process by which LPS is transferred from micelles to the TLR4-MD2 complex via LBP and CD14.
for more information, please refer to the original article:
J.-K. Ryu and S.J. Kim et al. Immunity 2017 46:38-50
* Lab information
Disease Molecule Biochemistry Laboratory (http://www.kaistdmbl.org/)