TLR9 traffics to an endosomal vesicle where it is processed by cathepsin S at neural pH to generate an N-terminal product (TLR9 N-ter, aa 1-723). The N-terminal fragment of TLR9 also binds ligand, but in contrast to the C-terminal fragment it inhibits TLR9 signaling. Thus, a proper balance between the two proteolytic events probably regulates TLR9-mediated host responses. (Chockalingam A et al 2011).
Cameron, JL, Brooks, JC, Chockalingam, A, Leifer, CA
cysteine-type endopeptidase activity of CTSS-like proteins [endolysosome lumen]
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