Open AccessProcessing and targeting of cathepsin L (TbCatL) to the lysosome in Trypanosoma brucei
Author(s) -
Koeller Carolina M.,
Bangs James D.
Publication year - 2019
Publication title -
cellular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.542
H-Index - 138
eISSN - 1462-5822
pISSN - 1462-5814
DOI - 10.1111/cmi.12980
Subject(s) - trypanosoma brucei , lysosome , biology , cathepsin l , cathepsin , cathepsin d , protozoa , microbiology and biotechnology , virology , axenic , computational biology , biochemistry , enzyme , genetics , gene , bacteria
Cathepsin L (TbCatL) is an essential lysosomal thiol protease in African trypanosomes. TbCatL is synthesized as two precursor forms (P/X) that are activated to mature form (M) with the removal of the prodomain upon arrival in the lysosome. We examine TbCatL trafficking in a novel system: truncated TbCatL reporter without the C‐terminal domain (CTD; TbCatL∆) ectopically expressed in an RNA interference (RNAi) cell line targeting the CTD/3′ untranslated region (UTR) of endogenous mRNA. TbCatL∆ is synthesized as P′/X′/M′ species, localizes to the lysosome, and rescues the lethal TbCatL RNAi phenotype. Inactive TbCatLΔ:C150A is only processed to M′ in the presence of endogenous TbCatL indicating trans ‐auto‐catalytic activation. X′ is formed with active endoplasmic reticulum (ER)‐retained TbCatLΔ:MDDL, but not with TbCatLΔ:C150A, indicating stochastic generation in the ER by cis ‐auto‐cleavage within the prodomain of newly synthesized P′. Modelling the TbCatL prodomain on the human CatL structure suggests three solvent accessible features that could contain post‐Golgi targeting signals: the N‐terminus, the helix 1/turn 1 junction, and a separate turn (T3). We demonstrate that the critical motif for lysosomal targeting is an asparagine‐proline dipeptide in T3 that is strictly conserved in all Kinetoplastida. These findings show novel insights on the maturation of TbCatL, which is a critical virulence factor in mammalian infection.