The mechanisms by which enzymes attach sulfur atoms to inert carbon centers are poorly understood despite the importance of these reactions in cellular metabolism and maintenance. One such sulfur-containing molecule of great importance is lipoic acid, an eight-carbon straight-chain fatty acid (octanoic acid) that has one sulfur atom appended to carbon 6 (C6) and one sulfur atom appended to carbon 8 (C8). It is used as a cofactor in several large protein complexes that are involved in energy production and storage, as well as in the metabolism of several amino acids. Despite the relatively detailed understanding of how lipoic acid functions in these complexes, it biosynthesis has been puzzling due to the limited understanding of how sulfur atoms are appended onto aliphatic carbon centers. This research seeks to assess the source of the appended sulfur atoms in this important sulfur-containing molecule and the mechanism of its biosynthesis. This project might provide a new paradigm for this type of chemistry for a large spectrum of C-S bond formation processes in metabolism. Outreach activities to encourage participation of underrepresented minority students in the STEM disciplines will be conducted.
This project focuses at the intersection of iron-sulfur cluster and lipoic acid biosynthesis and aims at providing a detailed molecular understanding of how aliphatic carbon centers are functionalized with sulfur atoms. Experiments have shown that a protein called NfuA, which itself is an iron-sulfur protein, can reinsert or repair the degraded auxiliary cluster on lipoyl synthase (LipA) after each turnover. In turn, NfuA obtains its cluster via a complex pathway by which iron-sulfur clusters are biosynthesized and trafficked. The aims of this project focus on elucidating the detailed mechanism that govern how the cluster on NfuA is transferred to LipA. Mössbauer spectroscopy and mass spectrometry will be used to follow iron and sulfur transfer, respectively. Protein crystallography will be used to monitor selenium transfer from NfuA containing a [4Fe-4Se] cluster to LipA, and efforts will be made to obtain structures of the NfuA/LipA complex. Lastly, electron paramagnetic resonance spectroscopy, as well as protein film voltammetry, will be used to study the unique serine ligation to the auxiliary cluster and to determine why it is critical for the reaction of LipA.
This project is jointly funded by the Molecular Biophysics Cluster in the Division of Molecular and Cellular Biosciences and the Chemistry of Life Processes Program in the Division of Chemistry.
