Research in the Torelli lab is broadly interested in the structural and chemical basis for enzyme function. The current focus is on enzymes that biosynthesize iron-sulfur (Fe-S) clusters (Figure 1), which are essential protein cofactors involved in a wide range of enzyme functions including electron transfer (e.g. respiration, photosynthesis), environmental sensing (e.g. redox homeostasis, iron deprivation), structural stabilization of protein folds and chemical catalysis (e.g. as Lewis Acids).
While the earliest enzymes probably assimilated Fe-S clusters that formed spontaneously in the environment, the evolution of photosynthesis and subsequent oxygenation of the atmosphere depleted available environmental sources of ferrous iron ions through oxidation to insoluble ferric iron species. As a consequence, pathways emerged to biosynthesize and deliver Fe-S clusters to enzymes requiring them for their function. Research in the Torelli lab is focused on several aspects of Fe-S biosynthesis.
First, we are interested in fundamental questions regarding how Fe-S clusters are formed by the biosynthetic machinery. For example, how are the toxic ferrous iron and sulfide ions combined to form nascent clusters? What electronic and structural modifications are required to form different Fe-S cluster species? How does a single biosynthetic pathway load Fe-S clusters into the diverse array of cellular proteins that require their function?
Second, one biosynthetic pathway in particular is highly upregulated during oxidative stress and iron starvation. How are the properties of the Fe-S clusters modulated during formation by this pathway to resist deleterious conditions? What specific protein:cluster interactions are required for biosynthesis during oxidative stress? Why haven’t other Fe-S biosynthetic pathways evolved similarly robust function that is less sensitive to adverse conditions?
Third, Fe-S clusters have chemical versatility and are natural chromophores. We are looking into novel applications of Fe-S proteins in areas of energy conversion and bioremediation.
Techniques employed in the Torelli lab include a variety of biophysical methods, especially X-ray crystallography. Other primary methods include electrochemical and spectroscopic analyses that are being performed in collaborations. Biophysical characterization (e.g. dynamic light scattering, size exclusion chromatography, ultracentrifugation) is also a focus, as well as standard molecular biology and microbiology methods used for bacterial overexpression and growth fitness trials.
Torelli, AT, Spitale, RC, Krucinska, J, and Wedekind, JE. (2008) Shared traits on the reaction coordinates of ribonuclease and an RNA enzyme, Biochem. Biophys. Res. Commun. 371, 154-158. PubMed
Spitale, R. C., Torelli, A. T., Krucinska, J., Bandarian, V., and Wedekind, J. E. (2009) The structural basis for recognition of the PreQ0 metabolite by an unusually small riboswitch aptamer domain, J. Biol. Chem. 284, 11012-11016 PubMed
Zhang Y, Zhu X, Torelli AT, Lee M, Dzikovski B, Koralewski RM, Wang E, Freed J, Krebs C, Ealick SE, and Lin H. Diphthamide biosynthesis requires an organic radical generated by an iron–sulphur enzyme. Nature 465:891-896 (2010). PubMed
Zhu X, Dzikovski B, Su X, Torelli AT, Zhang Y, Ealick SE, Freed JH, and Lin H. Mechanistic Understanding of Pyrococcus horikoshii Dph2, a [4Fe-4S] Enzyme Required for Diphthamide Biosynthesis. Mol. Biosyst. 7:74-81 (2011)t. PubMed