title: A peptidoglycan monomer with the glutamine to serine change and basic peptides bind in silico to TLR-2 (403-455).
abstract: Bacterial cell wall polysaccharides, such as PGN, bind and activate TLR-2, NOD2 and PGRP on monocytes/macrophages and activate inflammation. We found that the peptides containing basic amino acids (cations) at N -terminus and tyrosine at C-terminus interfered with activating ability of PGN. This finding is significant because the ECD of TLR-2 in vivo encounters a large number of proteins or peptides. Some should bind ECD and "pre-form" TLR-2 to respond or not to its activators, although they cannot activate TLR-2 alone. TLR-2 is receptor for a large number of ligands, including lipopeptides and bacterial cell wall glycoproteins. A binding site for lipopeptides has been identified; however, a binding site for soluble or multimeric PGN has not been proposed. To identify the candidate binding sites of peptides and PGN on TLR-2, we modeled docking of peptides and of the PGN monomer (PGN-S-monomer) to extracellular domain (ECD-TLR-2) of the unbound TLR-2. Quantification, in silico, of free energy of binding (DG) identified 2 close sites for peptides and PGN. The PGN-S-monomer binding site is between amino acids TLR-2, 404-430 or more closely TLR-2, 417-428. The peptide-binding site is between amino acids TLR-2, 434-455. Molecular models show PGN-S-monomer inserts its N -acetyl-glucosamine (NAG) deep in the TLR-2 coil, while its terminal lysine interacts with inside (Glu(403)) and outside pocket (Tyr(378)). Peptides insert their two N -terminal arginines or their C-terminal tyrosines in the TLR-2 coil. PGN did not bind the lipopeptide-binding site in the TLR-2. It can bind the C-terminus, 572-586 (DG = 0.026 kcal), of "lipopeptide-bound" TLR-2. An additional, low-affinity PGN-binding site is TLR-2 (227-237). MTP, MDP, and lysine-less PGN bind to TLR-2, 87-113. This is the first report identifying candidate binding sites of monomer PGN and peptides on TLR-2. Experimental verification of our findings is needed to create synthetic adjuvant for vaccines. Such synthetic PGN can direct both adjuvant and cancer antigen to TLR-2.
authors.affiliation: Department of Melanoma Medical Oncology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd, Houston, TX 77030, USA. yim_lee80@hotmail.com
authors.forename: Yufeng
authors.initials: Y
authors.lastname: Li
authors.forename: Clay L
authors.initials: CL
authors.lastname: Efferson
authors.forename: Rajagopal
authors.initials: R
authors.lastname: Ramesh
authors.forename: George E
authors.initials: GE
authors.lastname: Peoples
authors.forename: Patrick
authors.initials: P
authors.lastname: Hwu
authors.forename: Constantin G
authors.initials: CG
authors.lastname: Ioannides
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D019295:Computational Biology; D005973:Glutamine / Q000737:chemistry; D006801:Humans; D008262:Macrophage Activation / Q000276:immunology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010457:Peptidoglycan / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012694:Serine / Q000737:chemistry; D051195:Toll-Like Receptor 2 / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism
chemical_list: D010457:Peptidoglycan; C495342:TLR2 protein, human; D051195:Toll-Like Receptor 2; D005973:Glutamine; D012694:Serine