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National Institute of Environmental Health Sciences

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Publication Detail

Title: Molecular Basis of the Functional Differences between Soluble Human Versus Murine MD-2: Role of Val135 in Transfer of Lipopolysaccharide from CD14 to MD-2.

Authors: Vašl, Jožica; Oblak, Alja; Peternelj, Tina T; Klett, Javier; Martín-Santamaría, Sonsoles; Gioannini, Theresa L; Weiss, Jerrold P; Jerala, Roman

Published In J Immunol, (2016 Mar 01)

Abstract: Myeloid differentiation factor 2 (MD-2) is an extracellular protein, associated with the ectodomain of TLR4, that plays a critical role in the recognition of bacterial LPS. Despite high overall structural and functional similarity, human (h) and murine (m) MD-2 exhibit several species-related differences. hMD-2 is capable of binding LPS in the absence of TLR4, whereas mMD-2 supports LPS responsiveness only when mMD-2 and mTLR4 are coexpressed in the same cell. Previously, charged residues at the edge of the LPS binding pocket have been attributed to this difference. In this study, site-directed mutagenesis was used to explore the hydrophobic residues within the MD-2 binding pocket as the source of functional differences between hMD-2 and mMD-2. Whereas decreased hydrophobicity of residues 61 and 63 in the hMD-2 binding pocket retained the characteristics of wild-type hMD-2, a relatively minor change of valine to alanine at position 135 completely abolished the binding of LPS to the hMD-2 mutant. The mutant, however, retained the LPS binding in complex with TLR4 and also cell activation, resulting in a murine-like phenotype. These results were supported by the molecular dynamics simulation. We propose that the residue at position 135 of MD-2 governs the dynamics of the binding pocket and its ability to accommodate lipid A, which is allosterically affected by bound TLR4.

PubMed ID: 26826249 Exiting the NIEHS site

MeSH Terms: Amino Acid Sequence; Animals; Binding Sites; Biological Transport; Cell Line; Gene Expression; Humans; Hydrophobic and Hydrophilic Interactions; Lipopolysaccharide Receptors/metabolism; Lipopolysaccharides/metabolism; Lymphocyte Antigen 96/chemistry; Lymphocyte Antigen 96/genetics*; Lymphocyte Antigen 96/metabolism*; Mice; Models, Molecular; Molecular Sequence Data; Mutagenesis, Site-Directed; Protein Binding; Protein Conformation; Protein Interaction Domains and Motifs/genetics; Sequence Alignment; Structure-Activity Relationship; Toll-Like Receptor 4/metabolism

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