Mannose binding lectin and lung collectins interact with Toll-like receptor 4 and MD-2 by different mechanisms.
BACKGROUND
We have previously shown that lung collectins, surfactant protein A (SP-A) and surfactant protein D, interact with Toll-like receptor (TLR) 2, TLR4, or MD-2. Bindings of lung collectins to TLR2 and TLR4/MD-2 result in the alterations of signaling through these receptors, suggesting the immunomodulatory functions of lung collectins. Mannose binding lectin (MBL) is another collectin molecule which has structural homology to SP-A. The interaction between MBL and TLRs has not yet been determined.


METHODS
We prepared recombinant MBL, and analyzed its bindings to recombinant soluble forms of TLR4 (sTLR4) and MD-2.


RESULTS
MBL bound to sTLR4 and MD-2. The interactions were Ca2+-dependent and inhibited by mannose or monoclonal antibody against the carbohydrate-recognition domain of MBL. Treatment of sTLR4 or MD-2 by peptide N-glycosidase F significantly decreased the binding of MBL. SP-A bound to deglycosylated sTLR4, and this property did not change in chimeric molecules of SP-A/MBL in which Glu195-Phe228 or Thr174-Gly194 of SP-A were replaced with the corresponding MBL sequences.


CONCLUSIONS
These results suggested that MBL binds to TLR4 and MD-2 through the carbohydrate-recognition domain, and that oligosaccharide moieties of TLR4 and MD-2 are important for recognition by MBL. Since our previous studies indicated that lung collectins bind to the peptide portions of TLRs, MBL and lung collectins interact with TLRs by different mechanisms. These direct interactions between MBL and TLR4 or MD-2 suggest that MBL may modulate cellular responses by altering signals through TLRs.
Shimizu
Takeyuki
T
Department of Biochemistry, Sapporo Medical University School of Medicine, South-1 West-17, Chuo-ku, Sapporo 060-8556, Japan. stakeyu@sapmed.ac.jp
Nishitani
Chiaki
C
Mitsuzawa
Hiroaki
H
Ariki
Shigeru
S
Takahashi
Motoko
M
Ohtani
Katsuki
K
Wakamiya
Nobutaka
N
Kuroki
Yoshio
Y
D000818:Animals; D002478:Cells, Cultured; D037222:Collectins / Q000378:metabolism*; D006801:Humans; D008168:Lung / Q000378:metabolism; D051218:Lymphocyte Antigen 96 / Q000378:metabolism*; D037601:Mannose-Binding Lectin / Q000378:metabolism*; D011485:Protein Binding; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D018411:Spodoptera; D051197:Toll-Like Receptor 4 / Q000378:metabolism*
D037222:Collectins; D051218:Lymphocyte Antigen 96; D037601:Mannose-Binding Lectin; D011994:Recombinant Proteins; D051197:Toll-Like Receptor 4