Glycoconjugates play major roles in the infectious cycle of the trypanosomatid parasite Leishmania. While GDP-Fucose synthesis is essential, fucosylated glycoconjugates have not been reported in Leishmania major [H. Guo et al., J. Biol. Chem. 292, 10696–10708 (2017)]. Four predicted fucosyltransferases appear conventionally targeted to the secretory pathway; SCA1/2 play a role in side-chain modifications of lipophosphoglycan, while gene deletion studies here showed that FUT2 and SCAL were not essential. Unlike most eukaryotic glycosyltransferases, the predicted α 1–2 fucosyltransferase encoded by FUT1 localized to the mitochondrion. A quantitative “plasmid segregation” assay, expressing FUT1 from the multicopy episomal pXNG vector in a chromosomal null ∆fut1− background, established that FUT1 is essential. Similarly, “plasmid shuffling” confirmed that both enzymatic activity and mitochondrial localization were required for viability, comparing import-blocked or catalytically inactive enzymes, respectively. 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. Unexpectedly, a single rare ∆fut1− segregant (∆fut1s) was obtained in rich media, which showed severe growth defects accompanied by mitochondrial dysfunction and loss, all of which were restored upon FUT1 reexpression. Thus, FUT1 along with the similar Trypanosoma brucei enzyme TbFUT1 [G. Bandini et al., bioRxiv, https://www.biorxiv.org/content/10.1101/726117v2 (2021)] joins the eukaryotic O-GlcNAc transferase isoform as one of the few glycosyltransferases acting within the mitochondrion. Trypanosomatid mitochondrial FUT1s may offer a facile system for probing mitochondrial glycosylation in a simple setting, and their essentiality for normal growth and mitochondrial function renders it an attractive target for chemotherapy of these serious human pathogens.

The benefits of estrogens on bone health are well established; how estrogens signal to regulate bone formation and resorption is less well understood. We show here that 17β-estradiol (E2)-induced apoptosis of bone-resorbing osteoclasts is mediated by cleavage and solubilization of osteoblast-expressed Fas ligand (FasL). U2OS-ERα osteoblast-like cells expressing an EGFP-tagged FasL at the C-terminus showed decreased fluorescence following E2 treatment, indicative of a cleavage event. Treatment of U2OS-ERα cultures with a specific MMP3 inhibitor in the presence of E2 blocked FasL cleavage and showed an increase in the number of EGFP-FasL+ cells. siRNA experiments successfully knocked down MMP3 expression and restored full-length FasL to basal levels. E2 treatment of both human and murine primary osteoblasts showed up-regulation of MMP3 mRNA expression, and calvarial organ cultures showed increased expression of MMP3 protein and co-localization with the osteoblast-specific RUNX2 following E2 treatment. Additionally, osteoblast cell cultures derived from ERαKO mice showed decreased expression of MMP3, but not MMP7 and ADAM10, two known FasL proteases, demonstrating that ERα signaling regulates MMP3. In addition, conditioned media of E2-treated calvarial osteoblasts showed an approximate 6-fold increase in the concentration of soluble FasL indicating extensive cleavage, and soluble FasL concentrations were reduced in the presence of a specific MMP3 inhibitor. Finally, to show the role of soluble FasL in osteoclast apoptosis, human osteoclasts were co-cultured with MC3T3 osteoblasts. Both a specific MMP3 inhibitor and an MMP inhibitor cocktail preserved osteoclast differentiation and survival in the presence of E2 and demonstrate the necessity of MMP3 for E2-induced osteoclast apoptosis. These experiments further define the molecular mechanism of estrogen’s bone protective effects by inducing osteoclast apoptosis through upregulation of MMP3 and FasL cleavage.

Glycoconjugates play major roles in the infectious cycle of the trypanosomatid parasite Leishmania. Recently we showed that GDP-Fucose synthesis is essential, although fucosylated glycoconjugates have not been reported in Leishmania major. The Leishmania genome predicts at least five candidate fucosyltransferases, four of which appear targeted to the secretory pathway; SCA1 and SCA2 play a role in side-chain modifications of the abundant surface glycoconjugate lipophosphoglycan, while gene deletion studies here showed that FUT2 and SCAL were not essential. Unlike most eukaryotic glycosyltransferases, the predicted α 1-2 fucosyltransferase encoded by FUT1 localized to the mitochondrion. Enzymatic assays of tagged proteins expressed in vivo or of purified recombinant FUT1 showed it to have fucosyltransferase activity, with a relative broad substrate specificity including glycans and peptide substrates. A quantitative plasmid segregation assay, expressing FUT1 from the multicopy episomal pXNG vector in a chromosomal null Δfut1- background established that FUT1 is essential. We used plasmid shuffling to confirm that both enzymatic activity and mitochondrial localization were essential for viability, comparing import-blocked or catalytically inactive enzymes respectively. Unexpectedly a single rare Δfut1s mutant was obtained, which showed severe growth defects accompanied by mitochondrial dysfunction and loss, all of which were restored upon FUT1 re-expression. Thus, FUT1 along with the similar Trypanosoma brucei enzyme TbFUT1 (1) joins the eukaryotic O-GlcNAc transferases as one of the few glycosyltransferases acting within the mitochondrion. Current work is now oriented towards identifying the Leishmania fucosylated targets therein.

The trypanosomatid protozoan parasiteLeishmaniahas a significant impact on human health globally. Understanding the pathways associated with virulence within this significant pathogen is critical for identifying novel vaccination and chemotherapy targets. Within this study we leverage an ultradeep proteomic approach to improve our understanding of two virulence associated genes inLeishmania, encoding the Golgi Mannose/Arabinopyranose/Fucose nucleotide-sugar transporter LPG2, and the mitochondrial fucosyltransferase FUT1. Using deep peptide fractionation followed by complementary fragmentation approaches with higher energy collisional dissociation (HCD) and Electron-transfer dissociation (ETD) allowed the identification of over 6500 proteins, nearly doubling the experimentally knownLeishmania majorproteome. This deep proteomic analysis revealed significant quantitative differences in both Δlpg2-and Δfut1smutants withFUT1-dependent changes linked to marked alterations within mitochondrial associated proteins whileLPG2-dependent changes impacted many pathways including the secretory pathway. While the FUT1 enzyme has been shown to fucosylate peptides in vitro, no evidence for protein fucosylation was identified within our ultradeep analysis nor did we observe fucosylated glycans withinLeishmaniaglycopeptides isolated using HILIC enrichment. Combined this work provides a critical resource for the community on the observableLeishmaniaproteome as well as highlights phenotypic changes associated withLPG2orFUT1ablation which may guide the development of future therapeutics.

Leishmania is a widespread trypanosomatid protozoan parasite of humans, with ~12 million cases currently, ranging from mild to fatal, and hundreds of millions asymptomatically infected. This work advances knowledge of the experimental proteome by nearly 2-fold, to more than 6,500 proteins and thus provides a great resource to investigators seeking to decode how this parasite is transmitted and causes disease and to identify new targets for therapeutic intervention.