Roles of N-linked glycans in the recognition of microbial lipopeptides and lipoproteins by TLR2

Abstract

Details of roles of carbohydrates attached to Toll-like receptors (TLRs) in the recognition of pathogen-associated molecular patterns and in the formation of the functional receptor complex still remain unknown. This study was designed to determine whether the glycans linked at Asn114, Asn199, Asn414 and Asn442 residues of TLR2 ectodomain were involved in the recognition of diacylated lipopeptide and lipoprotein. Single and multiple mutants were transfected into human embryonic kidney (HEK) 293 cells together with a NF-κB luciferase reporter plasmid. All of these mutants were expressed on the surface. SDS-PAGE of the transfectants demonstrated that these mutants migrated lower than wild-type TLR2 and their molecular masses decreased as the number of mutated Asn residues increased. TLR2N114A, TLR2N199A and TLR2N414A as well as wild-type TLR2 induced NF-κB activation when stimulated with these ligands, whereas TLR2N442A failed to induce NF-κB activation. All of triple and quadruple mutants failed to induce NF-κB activation, but were associated with both wild-type TLR2 and TLR6 in the transfectants. TLR2N114A,N199A, TLR2N114A,N414A and, to a lesser extent, TLR2N114A,N442A, in which two N-linked glycans are speculated to be exposed to the concave surface of TLR2 solenoid, not only induce NF-κB activation but also are associated with wild-type TLR2 and TLR6. These results suggest that the glycan at Asn442 and at least two N-linked glycans speculated to be exposed to the concave surface of TLR2 solenoid are involved in the recognition of ligands by TLR2 and/or in formation or maturation of a functional TLR2 receptor complex. © 2006 The Authors; Journal compilation © 2006 Blackwell Publishing Ltd.