MD-2 is required for disulfide HMGB1-dependent TLR4 signaling.

Innate immune receptors for pathogen- and damage-associated molecular patterns (PAMPs and DAMPs) orchestrate inflammatory responses to infection and injury. Secreted by activated immune cells or passively released by damaged cells, HMGB1 is subjected to redox modification that distinctly influences its extracellular functions. Previously, it was unknown how the TLR4 signalosome distinguished between HMGB1 isoforms.

Genome-wide expression profiling and mutagenesis studies reveal that lipopolysaccharide responsiveness appears to be absolutely dependent on TLR4 and MD-2 expression and is dependent upon intermolecular ionic interactions.

Lipid A (a hexaacylated 1,4' bisphosphate) is a potent immune stimulant for TLR4/MD-2. Upon lipid A ligation, the TLR4/MD-2 complex dimerizes and initiates signal transduction. Historically, studies also suggested the existence of TLR4/MD-2-independent LPS signaling.

MD-2 residues tyrosine 42, arginine 69, aspartic acid 122, and leucine 125 provide species specificity for lipid IVA.

Lipopolysaccharide (LPS) activates the innate immune response through the Toll-like receptor 4 (TLR4).MD-2 complex. A synthetic lipid A precursor, lipid IV(A), induces an innate immune response in mice but not in humans.

MD-2-mediated ionic interactions between lipid A and TLR4 are essential for receptor activation.

Lipopolysaccharide (LPS) activates innate immune responses through TLR4.MD-2. LPS binds to the MD-2 hydrophobic pocket and bridges the dimerization of two TLR4.

Heterogeneity and dynamics in villin headpiece crystal structures.

The villin headpiece domain (HP67) is the C-terminal F-actin-binding motif that confers F-actin-bundling activity to villin, a component of the actin bundles that support the brush-border microvilli. It has been investigated extensively by both experimental and theoretical measurements. Our laboratory, for example, has determined both its NMR and its crystal structures.

Crystal structure of a pH-stabilized mutant of villin headpiece.

Villin-type headpiece domains are compact F-actin-binding motifs that have been used extensively as a model system to investigate protein folding by both experimental and computational methods. Villin headpiece (HP67) harbors a highly helical, thermostable, and autonomously folding subdomain in the C terminus (HP35), and because of this feature, HP67 is usually considered to be composed of a N- and C-terminal subdomain. Unlike the C-terminal subdomain, the N-terminal subdomain consists mainly of loops and turns, and the folding is dependent upon the presence of the C-terminal subdomain.

The differential impact of disulfide bonds and N-linked glycosylation on the stability and function of CD14.

Innate immunity is the first line defense against invading pathogens. During Gram-negative bacterial infection, the Toll-like receptor 4 and MD-2 complex recognize lipopolysaccharide present in the bacterial cell wall. This recognition can be enhanced 100-1000-fold by CD14.

High-resolution crystal structures of villin headpiece and mutants with reduced F-actin binding activity.

Villin-type headpiece domains are approximately 70 amino acid modular motifs found at the C terminus of a variety of actin cytoskeleton-associated proteins. The headpiece domain of villin, a protein found in the actin bundles of the brush border epithelium, is of interest both as a compact F-actin binding domain and as a model folded protein. We have determined the high-resolution crystal structures of chicken villin headpiece (HP67) at 1.