“I began my research career as a summer student at the National Institutes of Health (NIH), working on the problem of protein damage by reactive intermediates and its role in chemical toxicity.  However, there was no technology at the time to enable the identification of the protein targets.  During the 1980s and 1990s, my group at the University of Arizona worked on antioxidant chemistry of vitamin E, carotenoids and flavonoids and made extensive use of GC-MS and LC-MS/MS on a TSQ7000.  After hearing a talk by John Yates in 1998, I decided to move into proteomics and return to the problem of protein targeting by reactive intermediates.  We have worked with Finnigan LCQs ever since and, since my move to Vanderbilt, with Finnigan LTQs.  The new Finnigan LTQ is the instrumental mainstay of my research laboratory and of the Proteomics Laboratory at Vanderbilt.”

The Liebler lab at Vanderbilt is interested in how environmental factors affect health and disease by modifying cellular proteomes. The environmental factors they consider include pollutants, drugs, dietary components and physical agents such as sunlight. They believe that these environmental factors interact with different protein components in cellular proteomes.

In studying protein modifications, the Liebler lab has concentrated its efforts on developing LC-MS/MS on Thermo’s Finnigan LCQ and LTQ instruments in order to identify protein targets for chemical modification and to map modifications at the level of the amino acid sequence. They have extensively used recently developed methods to identify proteins based on sequence information and modifications.

The figure explains Liebler Lab ’s method towards identifying proteins and mapping modifications. They first digest proteins obtained from biological samples to peptides and then subject the digested peptides to LC-MS/MS. They analyze the resulting spectra by first searching against a sequence database using SEQUEST®. This helps identify protein components. They also use a new algorithm and software, called P-Mod, to automate the positional mapping of modifications.

In identifying protein targets of reactive chemicals, Liebler’s lab is making extensive use of the Finnigan LTQ and P-Mod. In previous work the Liebler laboratory has studied toxicologically significant model compounds, including quinones, aliphatic epoxides, halogenated hydrocarbons, and some toxic drug metabolites.   Currently, the major focus is the mapping of protein adducts formed by “endogenous electrophiles”, such as reactive products of lipid and glucose oxidation and the application of these products as biomarkers for diseases involving oxidative stress. 

The Liebler laboratory is also studying the mechanisms by which modifications of certain cellular protein sensors trigger adaptive responses to chemical and oxidative stress.  A related theme is the response of the ubiquitin superfamily of regulatory proteins and their regulation of cellular proteomes under external stress. Ubiquitin, a small protein performs key regulatory functions within the cell and often modifies several transcription factors under stress. Recent work in the Liebler lab and in other labs indicate that reactive chemicals and other environmental stressors can perturb the distribution of ubiquitin and the ubiquitin-like protein sumo. They hypothesize that such perturbations disrupt key regulatory mechanisms and lead to cellular perturbations and toxicity.

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Selected List of Publications:

1. Mason, D.E. and Liebler , D.C. (2003) Quantitative analysis of modified proteins by LC-MS-MS of peptides labeled with phenyl isocyanate.  J. Proteome Res. 2: 265-272.
2. Alderton, A.L., Faustman, C., Liebler , D.C. and Hill, D.W. (2003) Induction of redox instability of bovine myoglobin by adduction with 4-hydroxy-2-nonenal.  Biochemistry 42:  4398-4405.
3. Jones, J.A., Kaphalia, L., Moslen, M.T. and Liebler, D.C. (2003) Proteomic characterization of metabolism, protein adducts and hepatobiliary injury in rats exposed to 1,1-dichloroethylene and diclofenac.  Chem. Res. Toxicol.  16:  1306-1317.

* SEQUEST is a registered trademark of the University of Washington