Proteins are the workhorses of cells, adopting conformations that allow them to set off chemical reactions, send signals and transport materials. But when a scientist is designing a new drug, trying to visualize the processes inside cells, or probe how molecules interact with each other, they can’t always find a protein that will do the job they want. Instead, they often engineer their own novel proteins to use in experiments, either from scratch or by altering existing molecules.
Engineered proteins can be drugs that turn on or off signaling pathways in the body, imaging agents that light up other molecules or processes, or enzymes that produce molecules with commercial value. Now, researchers at the Salk Institute for Biological Studies have developed a new tool for such protein engineering: a way to add strong, unbreakable bonds between two points in a protein or between two proteins. The new technique was published August 4, 2013, in the journal Nature Methods.
“Even though you could modify proteins in lots of different ways, adding a new bond into a protein was not possible before this,” says senior study author Lei Wang, an associate professor in Salk’s Jack H. Skirball Center for Chemical Biology and Proteomics and holder of the Frederick B. Rentschler Developmental Chair.
When a protein folds from a loose chain of amino acid building blocks into its active three-dimensional structure, bonds and chemical interactions naturally form between different parts of the chain to keep the structure assembled. Most are relatively weak, driven by the electrochemical charges of different amino acids. Stronger bonds, called disulfide bridges, occur between pairs of cysteines, one particular amino acid. But for protein engineers, either type of bond has its own deficiencies. So linking two parts of a protein in a predictable and permanent way had been notoriously hard.
Wang and his collaborators wanted to be able to add strong, irreversible bonds —— called covalent bonds—— to proteins to alter their shape, make them more stable, or attach them to one another. They knew that cysteine amino acids reacted not only with other cysteines to make disulfide bridges, but with many other chemicals as well. So they began trying to create a new amino acid, different from the 20 that exist naturally, that cysteine would covalently bind to. They needed just the right compound, one that didn’t bind to cysteine too quickly but also didn’t bind too weakly.
Read more at: Phys.org