Researchers at the University of Illinois and the University of Connecticut have developed new brush polymers – synthetic protein-like molecules that catalyze their own formation – that could provide insight into enzyme behavior and self-replicating systems. The polymers have potential applications in catalyst development, nanomaterials and medicine.
As reported in the journal Nature Chemistry, the brush polymers consist of multiple spiral polymer chains branching out from a backbone. Such structures are not new, but this is the first demonstration of one capable of self-synthesizing, the researchers say.
The brush-like molecules can be used whole, or the spirals can be released from the backbone for applications that call for smaller structures, said study leader Jianjun Cheng, a professor of materials science and engineering at Illinois. Cheng’s group collaborated on the project with chemistry professor Yao Lin of the University of Connecticut.
“This is a very special nanomaterial. Because of the branched structure of the brush polymer, it can do things that other structures can’t do,” Cheng said. “In drug delivery, for example, the delivery agent has to go through the kidney, where there is 5- to 10-nanometer filtration. If the particle is too small, it gets filtered out and excreted, and can’t do its job.
“A lot of nanoparticles are made of a single polymer chain forming a globular structure, but once you get to the kidneys, it disassembles and gets filtered out. Because of the structure of the brush polymers, they don’t unfold into a line like other materials, so they can stay in the body for longer and have more time to find their targets.”
The researchers make the highly branched, brush-like molecules by adding protein building blocks to a solution of backbone scaffolds. The spirals grow up from the backbone simultaneously, quickly creating a set of identical spirals. The spirals cooperate with each other, helping each other grow. Because they catalyze their own growth in this way, the branched molecules form more than a thousand times faster than the process for making such spiral proteins on their own.
“The behavior of the brush polymer is absolutely unique,” said graduate student Ryan Baumgartner, the first author of the paper, “Cooperative polymerization of a-helices induced by macromolecular architecture.” “Nature actively utilizes polymer-based catalysts in the form of DNA, RNA and proteins to accelerate otherwise slow reactions to rates that allow life to sustain. Synthetically recreating the complexity and remarkable activity of these naturally occurring polymers is challenging and difficult. Not only that, but natural proteins frequently act to synthesize other proteins, but never themselves. The mechanism for the self-synthesizing phenomenon is directly related to the overall structure and shape of the polymer.”
The researchers can control the size and shape of the brush polymers by controlling how long to let the spirals grow, the length of the backbone and where the initiator points for spiral growth are placed along the backbone. They believe that the fundamental chemistry that enables this polymerization has potential in furthering the understanding of protein function and also in developing new and improved catalysts.
“We are working to understand the mechanism of this polymerization in more detail. The applications of these new structures are vast, but the mechanistic insights will be crucial to understanding how enzymes catalyze reactions fundamental for sustaining life,” Baumgartner said. “Because these structures show features of self-replication, they may even provide insight into the origin of life.”
The National Science Foundation supported this work.
Writer: Liz Ahlberg Touchstone, biomedical sciences editor, University of Illinois News Bureau, 217/244-1073, firstname.lastname@example.org.
Photo: L. Brian Stauffer.