A broadly active fucosyltransferase LmjFUT1 whose mitochondrial localization and catalytic activity is essential in the parasitic protozoan Leishmania
Summary (2 min read)
Introduction
- Glycoconjugates play major roles in the infectious cycle of the trypanosomatid parasite Leishmania.
- Enzymatic assays of tagged proteins expressed in vivo or of purified recombinant FUT1 showed it had a broad fucosyltransferase activity including glycan and peptide substrates.
- These studies have provided powerful tools leading to new insights on the requirements for LPG and related phosphoglycan -bearing molecules in both parasite stages within the mammalian and sand fly hosts (6, 7, 13-19).
- The essentiality of GDP-Fuc was unexpected since there are few reports of fucosylated molecules in Leishmania.
- Unexpectedly, FUT1 localizes within the parasite mitochondrion, an uncommon observation for glycosyltransferases.
Results
- Database mining for fucosyltransferase (FUTs)/ arabinopyranosyltransferase candidates in L. major Using a diverse collection of FUTs compiled from GenBank or CAZY databases (36), the authors searched the predicted L. major proteome for proteins showing significant similarities and/or conserved motifs.
- To confirm the surprising prediction of mitochondrial localization, the authors expressed a C-terminal HA-tagged FUT1 protein using the pIR1NEO vector as an episome; this construct was introduced into the ∆fut1- / +pXNGPHLEO-FUT1 line, yielding ∆fut1--/ +pXNGPHLEO-FUT1 / pIR1NEO-FUT1-HA (Fig. 2E).
- Similarly, 67 % of the dim cells also grew out, and subsequent tests showed that 96% (26/27) tested lacked GFP and were phleomycin sensitive, while retaining tagged FUT1-HA, yielding ∆fut1-/+ pIR1NEO-FUT1-HA (Fig. 2F).
- The authors confirmed the fucosyltransferase activity of recombinant FUT using enzyme expressed within Leishmania.
- The authors next tested whether the essential function of FUT1 required fucosyltransferase activity, perhaps through a structural role (52).
Discussion
- Previous studies have shown that GDP-Fucose synthesis is essential in trypanosomatids, yet for Leishmania and Trypanosoma brucei fucosylated molecules that might account for this requirement remained unknown.
- These data established that both mitochondrial localization and catalytic activity were required for essential FUT1 function.
- The authors were able to obtain only a single mutant completely lacking FUT1 entirely (∆fut1s; Figs. 7, 8).
- While two substrates for mammalian protein O-fucosyltransferase were inactive with LmjFUT1, two peptides predicted to be fucosylated in L. donovani functioned as acceptors, and MS/MS of the one tested confirmed fucosylation (Figs. 5B, S5).
- Proteomic surveys have revealed approximately 100 O-GlcNAc modified mitochondrial proteins (67-69), mostly encoded by nuclear genes raising the possibility of glycosylation prior to mitochondrial import (70).
Materials and Methods.
- L. major strain FV1 (LmjF or WT; WHO code MHOM/IL/80/Friedlin) was grown at 26°C in M199 medium (U.S. Biologicals) containing 10% heat-inactivated fetal bovine serum and other supplements and transfected by electroporation using a high voltage protocol as described (73, 74).
- Molecular methods were performed as described (30).
- For plasmid shuffling experiments, Δfut1-/ +pXNG-FUT1 was further transfected with episomal pIR1NEO (B6483) into which test FUT1 genes had been inserted (Table S1).
- Samples were viewed with a JEOL 1200EX transmission electron microscope (JEOL USA Inc., Peabody, MA).
- For biorthogonal labeling, parasites were inoculated into M199 medium at 1 x 105/mL (WT or Δlpg2-) or 3.8 x 106/ml (Δfut1s) and grown for three days in the presence/absense of 100µM alkyne fucose (Invitrogen C10264), after which parasites were washed in PBS.
Legend to Figure 6.
- CAT-MUT-HA has an R297A substitution; MTP-MUT-HA replaces two Glu residues in the MTP with Arg ; BLOCK-MUT-HA has the cytoplasmic protein PTR1 fused to the N-terminus.
- The results of mitochondrial localization tests (Panel D) and plasmid shuffling tests (Panel C) are summarized on the right of the illustrations.
- Growth in the absence of phleomycin and FACS sorting of ‘dim’ and ‘bright’ cells was performed as described in Fig. Δfut1-pXNG-FUT1/pIR-MUT-HA lines was grown for 24 h in the absence of phleomycin, and analyzed by GFP flow cytometry.
- Indirect immunofluorescence of HA tagged FUT1 expressed from pIRNEO in the Δfut1-/ +pXNGPHLEO-FUT1 background, also known as Panel D.
- The average and standard deviation of three preparations is shown.
Legend to Figure 8
- M, mitochondria; k, kinetoplast; black arrow, normal mitochondrial cristae; white arrows, aggregates inside mitochondria; star, bloated cristae.
- BglII forward primer to amplify ORF of LmjFUT1 SMB3956 CCCAGATCTTCAGATGAGTATCCATCCAGGG.
- L-SAT FUT1 primer a = l-PAC = l-WT (Fig. S3) SMB3990 CCCAGATCTCCACCATGCCTGATAATAGATACGGC.
Did you find this useful? Give us your feedback
References
467 citations
413 citations
396 citations
367 citations
340 citations
Related Papers (5)
Frequently Asked Questions (2)
Q2. What have the authors stated for future works in "A broadly active fucosyltransferase lmjfut1 whose mitochondrial localization and catalytic activity is essential in the parasitic protozoan leishmania" ?
Future studies will address this possibility. Future studies will be necessary to resolve the nature of the GDP-Fucose and FUT1dependent product ( s ) in trypanosomatids, which genetic and biochemical data strongly predict must nonetheless exist. Potentially, trypanosomatid mitochondrial FUT1s may offer a facile system in the future for probing mitochondrial glycosylation in a setting uncomplicated by multiple isoforms targeted to diverse compartments, and its essentiality renders it an attractive target for chemotherapy of trypanosomatid parasites. L. donovani expresses a mannose-fucose conjugate whose structure has not been definitively established ( 33 ), and several L. donovani proteins exhibited MS/MS signatures suggestive of fucosylation ( 34 ).