OpeRATOR Publication from Johns Hopkins University
Scientists from the prestigious Johns Hopkins University School of Medicine have used OpeRATOR to develop a workflow to map O-glycosylated sites on proteins in very complex samples. O-glycoproteins are notoriously difficult to study due to the low abundance, high structural heterogeneity and low stability. Previous approaches using affinity enrichment or engineered cell culture systems either lack efficiency or are ill-suited forO-glycoproteomic studies of complex samples.
In the workflow developed by Weiming Yang and colleagues, protein samples such as serum or kidney tissue were digested with trypsin, immobilized onto beads through the N-terminus and treated with OpeRATOR and SialEXO. OpeRATOR is an endoprotease and derived from the gut commensal bacteria Akkermansia muciniphila that specifically cleaves peptides and proteins N-terminally of O-glycosylated serine or threonine residues. Therefore, only O-glycopeptides are released from the solid support and were identified using ETD mass spectrometry.
Using this workflow, Yang et al. were able to map over 3000 O-glycosylation sites from human serum, T cells and kidney tissue, almost doubling the number of known O-glycosylation sites. They were also able to detect and quantify the aberrant O-glycosylation patterns in kidney tumors, showcasing the potential use of such methodologies for both basic research and diagnostic purposes.
Meet the Scientist
We got the opportunity to interview the first author of the paper, Weiming Yang at Johns Hopkins University.
Tell us about yourself?
I am a Research Associate in Mass Spectrometry Core Facility in the Center for Biomarker Discovery and Translation (
www.biomarkercenter.org) of the Johns Hopkins University. The Mass Spectrometry Core Facility carries large-scale proteomics with particular emphasis on protein glycosylation on proteome scale to elucidate functions of glycoproteins on biology and disease. Before this position, I was a postdoc fellow in the same lab and worked on innovative glycoproteomics methods and HIV research. My interest in protein O-linked glycosylation started from every beginning at Hopkins that I was able to identify an O-linked glycosylation site in HIV gp120 from the infectious virion. Later on, I developed a series of glycoproteomic methods to study protein N- and O-linked glycosylation. The development of novel glycoproteomic methodologies led to new areas toward the discovery of the biomarker for HIV reservoir and new insight into cancer biology.
What is new with the ExoO method you have developed?
The major advantage of EXoO is its applicability to analyze clinical samples that is a breakthrough and central to reveal the significance of protein O-linked glycosylation in diseases. Using EXoO, now, scientists can start to gain new insight into their biological systems regarding O-linked glycoproteins. O-linked glycoproteins are ubiquitous on the cell surface and extracellular environment that is highly relevant to new treatment for diseases and diagnostics. Also, the EXoO is advantageous to analyze mucin-type O-linked glycoproteins that cannot be easily analyzed by conventional methods. The EXoO method identifies a large number of O-linked glycosylation sites in the sample that may be easily identified by using other methods such as various enrichments coupled with ETD-MS/MS.
How did you perform the analysis prior to this method?
We tried to use the same solid phase method to immobilize the peptides but released O-glycopeptides using beta-elimination to study site of protein O-linked glycosylation. Beta-elimination is a chemical reaction that can tag the site of protein O-linked glycosylation but give some background release of peptides from the solid support. We tried ETD-MS/MS for O-linked glycopeptide analysis but the number of identification is lower than the use of the current method using EXoO to release the O-glycopeptides.
What are the benefits of applying Operator in the workflow?
The OpeRATOR enzyme is a key component in the workflow. The high specificity of OpeRATOR enabled release of site-specific O-linked glycopeptides from solid phase support. Therefore, the resulting glycopeptides are relatively pure for improved identification.
What can you tell us about what you currently are working on?
Currently, we are applying the method to study different diseases including cancers and HIV reservoir.
How would you describe the impact of OpeRATOR on the O-glycan field?
The discovery of OpeRATOR changes of the game in the field of O-linked glycoproteomics. It makes the analysis of large-scale and site-specific O-linked glycoproteome in clinical samples feasible. For O-glycans, the specificity of OpeRATOR is not completely clear that will need further investigation. O-glycans have many different structures. The glycomic methods may still be the best way to go.
What are your thoughts on the future of O-glycan analysis?
EXoO and OpeRATOR provide unique research tools to identify the site of O-linked glycosylation. So far, the evidence supports that core 1 Gal-GalNAc structure can be studied by the use of OpeRATOR. Glycomic method focus on the identification of all different O-glycan structures with linkage and quantitative information. In the future, the structures of O-linked glycans on the specific sites on the proteins can be revealed in a single workflow.
For more information on OpeRATOR go the the following pages:
The full text paper is available online:
