Edgington-Mitchell, L. | bioRxiv Science

bioRxiv2019

Tissue-ABPP enables high-resolution confocal fluorescence imaging of serine hydrolase activity in cryosections - Application to glioma brain unveils activity hotspots originating from tumor-associated neutrophils

Serine hydrolases (SHs) are a functionally diverse family of enzymes playing pivotal roles in health and disease and have emerged as important therapeutic targets in many clinical conditions. Activity-based protein profiling (ABPP) using fluorophosphonate (FP) probes has been a powerful chemoproteomic approach in studies unveiling roles of SHs in various biological systems. The ABPP approach utilizes cell/tissue proteomes and features the FP warhead, linked to a fluorescent reporter for in-gel fluorescence imaging or a biotin tag for streptavidin enrichment and LC-MS/MS-based target identification. Here, we advance the ABPP methodology to glioma brain cryosections, enabling high-resolution confocal fluorescence imaging of SH activity in different cell types of the tumor microenvironment, identified by using extensive immunohistochemistry on activity probe labeled sections. We name this technique tissue-ABPP to distinguish it from conventional gel-based ABPP. We show heightened SH activity in glioma vs. normal brain and unveil activity hotspots originating from tumor-associated neutrophils. Thorough optimization and validation is provided by parallel gel-based ABPP combined with LC-MS/MS-based target verification. Tissue-ABPP enables a wide range of applications for confocal imaging of SH activity in any type of tissue or animal species.

cancer biology↗

bioRxiv2019

Loss of O-linked protein glycosylation in Burkholderia cenocepacia impairs biofilm formation and siderophore production via alteration of quorum sensing regulation

O-linked protein glycosylation is a conserved feature of the Burkholderia genus. For Burkholderia cenocepacia, the addition of the trisaccharide {beta}-Gal-(1,3)--GalNAc-(1,3)-{beta}-GalNAc to membrane exported proteins is required for virulence and resistance to environmental stress. However, the underlying causes of the defects observed in the absence of glycosylation are unclear. This study demonstrates that the global B. cenocepacia proteome undergoes dramatic changes consistent with alterations in global transcriptional regulation in the absence of glycosylation. Using luciferase reporter assays and DNA cross-linking analysis, we confirm the repression of the master quorum sensing regulon CepR/I in response to the loss of glycosylation, which leads to the abolition of biofilm formation, defects in siderophore production, and reduced virulence. The abundance of most of the known glycosylated proteins did not significantly change in the glycosylation-defective mutants except for BCAL1086 and BCAL2974, which were found in reduced amount, suggesting they could be degraded. However, the loss of these two proteins was not responsible for driving the proteomic alterations, as well as for reduced virulence and siderophore production. Together, our results show that loss of glycosylation in B. cenocepacia results in a global cell reprogramming via alteration of the CepR/I regulon, which cannot be explained by the abundance changes in known B. cenocepacia glycoproteins.\n\nIMPORTANCEProtein glycosylation is increasingly recognised as a common protein modification in bacterial species. Despite this commonality our understanding of the role of most glycosylation systems in bacterial physiology and pathogenesis is incomplete. In this work, we investigated the effect of the disruption of O-linked glycosylation in the opportunistic pathogen Burkholderia cenocepacia using a combination of proteomic, molecular and phenotypic assays. We find that in contrast to recent findings on the N-linked glycosylation systems of Campylobacter jejuni, O-linked glycosylation does not appear to play a role in proteome stabilization of most glycoproteins. Our results reveal that virulence attenuation observed within glycosylation-null B. cenocepacia strains are consistent with alteration of the master virulence regulator CepR. The repression of CepR transcription and its associated phenotypes support a model in which the virulence defects observed in glycosylation-null strains are at least in part due to transcriptional alteration and not the direct result of the loss of glycosylation per-se. This research unravels the pleotropic effects of O-linked glycosylation in B. cenocepacia, demonstrating that its loss does not simply affect the stability of the glycoproteome, but also interferes with transcription and the broader proteome.

microbiology↗