Immobilized Enzymes Promise Alternative To Cyanogen Bromide's Toxicity
A conversation with Robert Hughes, Ph.D., East Carolina University
For decades, the standard protocol for liberating recombinant peptides from their fusion partners has relied on cyanogen bromide (BrCN). Although it is effective at C-terminal cleavage of methionine residues, BrCN is a highly toxic, volatile solid that presents significant danger to anyone handling it and demands rigorous and expensive waste disposal protocols. In an era where the biopharmaceutical industry is pivoting toward green chemistry and intensified safety standards, the search for a cleaner, more surgical alternative has intensified.
Robert Hughes, Ph.D., has been exploring alternatives at his East Carolina University lab. At the CHI PepTalk conference in January, he described a promising shift away from hazardous chemical cleavage by using site-specific proteases anchored to solid supports. Researchers achieved high-precision processing without the environmental and safety overhead of traditional reagents.
We met Hughes at the conference where he offered to answer a few questions about his work. Our conversation explores the technical hurdles of this transition — specifically, addressing the historical Achilles' heel of enzyme-based methods: leaching. Hughes explains how covalent attachment chemistries, such as HaloTag technology, ensure that the enzyme remains bound to its matrix, preventing downstream contamination and simplifying purification.
As the industry moves from traditional biologics into more complex modalities, these refined cleavage strategies offer a path toward more sustainable and robust CMC frameworks. The video transcript below is edited for clarity.
Your research explored alternative cleaving methods of histatin peptides, especially in E. coli. Beyond the environmental impact, how much does removing cyanogen bromide from a safety perspective, simplify things for people doing the work?
Hughes: BrCN historically has been used to cleave peptides from fusion proteins and, although its usage has already fallen out favor somewhat, you still see protocols in which people are using it. We've proposed replacing it with mobilized enzyme strategies. In the early days of recombinant peptide production, mobilized enzymes, or site-specific proteases, were not easily accessible, so BrCN was a really important reagent then. Now, we have many, many types of proteases that we can choose from to accomplish our goal.
How do you address the risk of an enzyme or its support matrix leaching into the product stream, creating downstream complications, particularly in purification?
Hughes: That was actually a big problem for us early on in our research. We initially used some non-covalent approaches to putting the enzymes on our nanoparticles or beads. Eventually, we moved to a HaloTag chemistry, which forms a covalent link to an alkyl halo ligand that can be chemically attached to a bead or particle. That covalent attachment eliminates a lot of the concern about enzyme leaching.
Now, the actual matrix that you're using to immobilize the enzyme, that's another concern. You don't want that to end up in your downstream workflow. It seems to be less of an issue for us doing the protein and peptide production pipelines.
In some of our other projects where we're using organo-catalytic approaches to make small molecules, we're using immobilized enzymes to catalyze those carbon-carbon bond coupling transformations. Either due to the harsh nature of the solvents we're using, or due to the physical agitation required with stir bars and so forth, you can actually decompose your immobilized enzyme matrix, and that can end up in your solution. That's a problem we're just starting to address right now.
Enzymes are generally more expensive than BrCN, but how does removing the hazardous waste disposal and extra protocols associated with BrCN use impact cost of goods?
Hughes: Once you have the plasmid or the strain of your enzyme for production in hand, your cost will rapidly go down in comparison to the chemical reagent even though, initially, the reagent is much cheaper. The other part is, compared to a chemical method, you're eliminating lots of solvents and other things that are expensive and hazardous to the environment. There are many different types of savings that can be realized over the long term through recombinant immobilized enzyme approaches.
Is the immobilization strategy plug-and-play for any protein? Does a new peptide require custom engineering?
Our goal is for it to be generalizable. Where it might not be generalizable is if there's an issue with substrate accessibility: for instance, when the fusion protein and the protein of interest are not accessible to the immobilized enzyme. In those cases, you can either re-engineer your immobilized enzyme by including flexible linkers and other things of that nature, or you can add your immobilizable enzyme — in the non-mobilized form — and use that to cleave your protein of interest because, generally, greater degrees of freedom make that possible. Then, you can capture that with your resin at the end stage of your process.
About The Expert:
Robert M. Hughes, Ph.D., is an associate professor of biological chemistry at East Carolina University. His lab develops protein- and small-molecule-based reagents for the control and monitoring of biochemical pathways. He received his Ph.D. in bio-organic chemistry and conducted postdoctoral research at the University of North Carolina - Chapel Hill. He also held a postdoctoral position at Duke University. Connect with him on LinkedIn.