Professor of Chemistry
Second Lieutenant, Military Service, 1981-1983
Research Focus in the MetalloBiomolecule Interest Group (MBIG)
Our research involves the use of spectroscopic methods, e.g., nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR and pulsed EPR), and electronic spectroscopies, kinetic and thermodynamic methods, and biochemical methods for the study of hydrolytic chemistry and for the studies of the structure and function of some metalloproteins, metallo-biomolecules, and synthetic model complexes.
(I) Hydrolytic Chemistry
Hydrolysis is one of the most important chemical, biological, industrial, and environmental processes that is involved in novel synthesis, food processing, and biological digestion, regulation, and recycling, and degradation of pesticides and stockpiles of nerve agents. A number of Zn(II) enzymes are involved in various hydrolytic reactions, such as phosphoester and peptide hydrolysis. One common feature among these enzymes is the presence of a coordinated water molecule that is activated by the Zn(II) to a factor of >107 in terms of its pKa. A significant difference is the structures of the substrates. For example, the tetrahedral configuration of phosphoesters only resembles the gem-diolate transition state configuration of peptides formed upon nucleophilic attack at the scissile peptide bond by the Zn(II)-activated water molecule during hydrolysis. (However, we have recently discovered a unique "alternative catalysis" in which a phosphodiester is hydrolyzed at a remarkable rate by a di-Zn aminopeptidase from Streptomyces. See abstract.)
Several hydrolytic metalloenzymes are under investigation in our group, including the unique Zn-containing endopeptidase astacin family (including BP10 from sea urchin embyros recently expressed in our laboratory in collaboration with Dr. Brian Livingston at the Biology Department of the University), di-Zn aminopeptidase, and tri-Zn phospholipase C.
(B) Model Systems
Chemical models that mimic the active site metal environment and/or the function of metallohydrolases are built for the investigation of the spectroscopic properties and water activation of the enzymes. Several model systems have been studied in our laboratory to establish their hydrolytic capability. These systems include metallopolymers, metal-binding natural products and synthetic compounds, as well as metallopeptides. (Read more here!)
While many antibiotics do not require metal ions for their biological activity, there are several families of antibiotics which require metal ions to function properly, including bleomycin, streptonigrin, bacitracin, and possibly the anthracyclines. In some of these metal-dependent antibiotics, metal ions are bound tightly and are integral parts of the structure and function of the antibiotics. Removal of the metal ions from these antibiotics results in deactivation and change in structure. Similar to the case of “metalloproteins”, these antibiotics are thus dubbed “metalloantibiotics” in our laboratory.
There are a number of antibitoics which form stable metal complexes with metal ions, such as the di- and tri-valent complexes of bleomycin and streptonigrin, Ca(II)/Mg(II) and Fe(III) complexes of tetracyclines, and divalent metal complexes of bacitracin. The metal ions are involved in the proper action of these antibiotics. For example, the binding of redox active metal ions to bleomycin and streptonigrin entitles these antibiotics to act as potent DNA cleavaging agents, and the divalent metal complexes of bacitracin can bind long-chain isoprenyl pyrophosphates which results in the inhibition of cell wall synthesis.
(III) Chemistry of the Alzheimer's disease-related
The chemistry of redox-active metal complexes of β-amyloid peptide (Aβ) has been an area of intense focus in the study of Alzheimer's disease (AD). The aggregation of Aβ within the neocortex is closely related to the pathology of AD and has been shown to be induced by metal binding. The Aβ peptides are generated by the cleavage of the ubiquitous amyloid precursor protein (APP) by α, β, and γ secretases. Aβ in the form of insoluble plaques contains up to mM amounts of Zn2+, Cu2+, and Fe3+ in the neocortical region of the brain; however, the cause/effect connection of the metallo-Aβ plaques with AD is still under debate. Since Aβ1-42 and Aβ1-40 have been shown to bind metal ions with high apparent affinity constants, understanding of the metal-binding domain and its structure and chemistry may shed light on the neuropathology of AD. We study the redox chemistry of metallo-Aβ, with particular emphasis on metal-centered oxidative activities toward redox-sensitive compounds, including catecholamine neurotransmitters. Recent studies can be found in our JBC and Angew. Chem. publications.
(IV) NMR Studies of Paramagnetic Molecules
The large paramagnetism of the unpaired electrons results in significant shortening in nuclear relaxation times (in the range of ms) and gives rise to isotropically shifted 1H NMR signals that can reach several hundred ppm. These signals are attributable to the protons in the proximity of the metal ions. Thus, paramagnetic metal ions can be used as NMR probes for the investigation of the structure of the metal binding environment in biomolecules and synthetic metal complexes, and the interactions of ligands with the metal centers. One- and two-dimensional NMR techniques have been developed and applied to the study of paramagnetic compounds in our research group as outlined below.
A Book Chapter on NMR of Paramagnetic
Authored "Nuclear Magnetic Resonance of Paramagnetic Metal Centers in Proteins and Synthetic Complexes" (see table of contents) In Physical Methods in Bioinorganic Chemistry, Spectroscopy and Magnetism, Que, L., Jr., Ed.; (see book information) University Science Books; 2000.
We currently collboarate with Dr. Alexander Angerhofer at University of Florida on pulsed EPR studies of the Cu2+ derivatives of serralysin and astacin and other Cu2+-containing systems, Dr. Sanboh Lee (李三保) at the National Tsing Hua University on EPR studies of irradiated polymers, and Dr. Jyh-Fu Lee (李志甫) at the National Synchrotron Radiation Research Center (NSRRC) (Taiwan) and Dr. Hua-Feng Hsu (許鏵芬) at the National Cheng Kung University (Taiwan) on X-ray absorption spectroscopic studies of metallopolymers and with Dr. Andrew Terentis at Florida Altantic University on Raman spectroscopic studies of oxy-Cu centers.
We have also been involved in the use of 1D and 2D NMR and kinetic methods for the investigation of several metalloenzymes provided by our collaborators, including carbonic anhydrase in collaboration with Dr. David Silverman, the enzyme nitrate reductase in collaboration with Dr. Andrew Cannons (Biology), Dr. Larry Solomonson (Biochemistry), and Dr. Michael Barber (Biochemistry) of the University, with Dr. Brian Livingston at the Biology Department of the University (now at the Department of Biological Sciences of California State University at Long Beach) on molecular biology in expression of metalloproteins, prolyloligopeptidase (POP) from the hyperthermophilic Archaeon Pyrococcus furiosus with Dr. Valerie Jody Harwood of the University (Biology), the heme-based oxygen sensor FixL kinase in nitrogenase synthesis in collaboration with Dr. Marie Alda Gonzalez of Ohio State University (now at University of Texas Southwestern Medical Center at Dallas), the urease accessory protein UreE in collaboration with Dr. Robert Hausinger of Michigan State University, and CuCu-aminopeptidase with Dr. Richard Holz at Utah State University, and metallo-dendrimers in collaboration with Dr. George Newkome of the Department (now at the University of Akron).
For questions about the graduate research in bioinorganic chemistry at USF
Email Dr. Li-June Ming at: email@example.com
Updated Spring, 2001