This CAREER award in the Inorganic, Bioinorganic and Organometallic Chemistry program supports work by Professor Pinghua Liu at Boston University to study the biosynthesis and biodegradation of phosphonates (C-P bond containing compounds). Phosphonates exist widely in nature and many have biological functions. In addition, because of the wide use of man-made phosphonates (e.g., pesticides, agricultural insecticides) and the extremely inert nature of the C-P bond, phosphonates have accumulated in the environment and are a major source of both land and water pollution. To date, there is only one characterized C-P bond formation enzyme, phosphoenolpyruvate isomerase. The enzyme to be studied in this project, BcpD, is the second enzyme capable of catalyzing the C-P bond formation. Specifically, the roles of two cofactors, the iron-sulfur cluster and cobalamin are being investigated. These mechanistic studies in the first part of the proposed effort will enable the design of methods for phosphonate profiling (identities and concentration of phosphonates in a cell). The second half of the work will identify genes responsible for phosphonate degradation in bacteria, which will eventually allow the development of green chemistr to degrade pollutants using bioengineering. The research is integrated into the PI's educational activities, which aim at addressing significant issues in the training of the next generation of bioscientists, specifically: 1) their need to acquire a global perspective of the technical challenges faced by society, e.g., environmental protection; 2) the creation of opportunities for the early participation of high school and undergraduate students in the sciences; and 3) the need for the interdisciplinary training of scientists to better equip them to address the 21st century's chemical, biological, and technological challenges.
With support from NSF CAREER award, we have successfully developed an interdisciplinary research program in the Liu laboratory by integrating a few disciplines (synthetic organic chemistry, bichemistry, biophysical spectroscopy, and molecular biology). At the same time, we have efficiently integrated our interdisciplinary research program with our proposed education mission: encourage the the participation of our students in biological research at the early stage of their career. Our studies focus on the mechanistic studies of iron-containing metallo-enzymes in natural product biosyntheses as well as degradation. Phosphonates are chosen as one of our molecular targets. Phosphonates (carbon–phosphorus bond containing compounds) is a unique class of natural products with many interesting biological activities. As a result, they have been widely used in medicine or agriculture. There are a few dozen natural phosphonates. Despite their interesting biological activities, the biosynthetic schemes for the majority of them have not been studied yet. One of the molecules chosen in our study is bialaphos. It’s proposed biosynthetic scheme involves nearly 20 steps. To study such a complicated biosynthetic process, a few approaches were employed. First, the pathway were divided into a few parts and three of the key proposed synthetic intermediates were synthesized using synthetic organic chemistry; Second, we have successfully overexpressed and purified all except 2 of the enzymes of the whole pathway (molecular biology); 3) We chose a few interesting steps (metallo-enzyme catalyzed steps) to work with (enzymology and spectroscopy). One type is the mononuclear non-heme iron enzyme (e.g., PhpD) and the other type is the unique iron-site containing [4Fe-4S] proteins (e.g., Pmi and BcpD). The most challenging part is that the non-heme iron enzyme is an oxygenase, while those [4FE-4S] proteins are oxygen sensitive reductases. After successfully integrate the knowledges from various disciplines, we have successfully setup both oxygenase and reductase systems. In addition, the knowledge gained from those studies have also been applied to study C-O and C-N bond cleavage reactions using similar types of chemistry. Many of these enzymes catalyze novel transformation with no or few precedents in literature. Our education program focuses on attracting students to participate in research at the early stage of their career. The interdisciplinary program supported by this award offers an excellent platform to realize our education mission. In the last 5 years, 22 undergraduate students have been participated in our research programs. Among those 22 students, 13 have received UROP or REU awards and 8 of them have been co-authors in our publications. In addition, a few more of them have manuscripts in preparations.
