by Violet Wallerstein
Dr. Cassano is a biochemistry professor at Drew University. In his time at Drew, Dr. Cassano has worked on the mechanisms involved in breaking a phosphodiester bond.
Phosphodiester bonds are one of the most important bonds in biology, as they hold DNA and RNA together. They are also critical to many secondary messengers in cellular signaling. They have inherent biological importance, and their function in secondary messengers also adds medical importance. Phosphodiester bonds are thermodynamically unstable but kinetically stable. DNA is generally stable, but it can also be made favorable to cleave when necessary. There are many enzymes that are designed to cleave these bonds.
Metal ions are involved in catalyzing the reaction of cleaving the phosphodiester bonds. The phosphate group has a negative charge, and so does the molecule or nucleophile that wants to break it, so the positive charge of a metal ion helps the nucleophile get close to the phosphodiester backbone to break it. In Dr. Cassano’s lab, he uses the hydroxide ion or internal hydroxyl groups as nucleophiles.
There are many enzymes that use these metal cofactors, and there are two ways to look at how the metal ions are contributing to catalysis. One way is changing the enzyme to make it unable to bind to its metal cofactor. This route can possibly change the rest of the enzyme and how it functions, showing the upper limit of what the metal contributes.
Dr. Cassano’s lab looks at the lower limit of what the metal ion can do by looking at how the reaction catalyzes with only the metal ion in aqueous solution.
This work began for Dr. Cassano when he first started at Drew about 14 years ago, though the questions leading to these experiments began forming during his years at graduate school. Dr. Cassano likes his research because he likes going into the details of a reaction. He enjoys “trying to look at a structure, and the structure makes sense, but the question is how much? I’ve always been interested in enzyme catalysts because they are just about the best catalysts on Earth.” DNA, whose half life is about 100,000 years if the carbon is attacked but almost a billion years if the phosphate is attacked, can be cleaved in less than a second with the help of an enzyme.
As with any research, there are some problems that present themselves. Dr. Cassano has had trouble trying to synthesize one product but obtaining a mixture instead; the real difficulty is in identifying what the products are. The amounts used in his lab are very small and so typical classification methods such as NMR are not useful.
Dr. Cassano teaches Chem 161, 360, 361, and 362. Talk to him in his office on the third floor of the hall of sciences to learn more about his research!
