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Li-June Ming(明立君) Professor of Chemistry
The (now Second Lieutenant, Military Service, 1981-1983
Bioinorganic Chemistry |
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RESEARCH INTERESTS PUBLICATION LIST/AWARDS
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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.)
(A) Metallohydrolases
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!)
(II) "Metalloantibiotics"
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
metallo-β-amyloid
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.
- Several paramagnetic lanthanide (III) ions have been used as NMR probes for the study of Ca(II) proteins, including α-lactalbumin and EF-hand proteins, and some anticancer antibiotics, including anthracyclines and streptonigrin. (A summary)
- Several paramagnetic transition metal ions, including Co(II), Ni(II), and Cu(II), have been used as NMR probes for the study of the metal binding sites in metalloproteins, including several hydrolytic metalloenzymes, two heme proteins, and other mtalloproteins. (See below.)
- Metalloantibiotics, including anthracyclines, streptonigrin, and aureolic acids, and their interactions with DNA have been studied by means of NMR techniques. The structure and function relationship of the widely used peptide antibiotic bacitracin has also been studied by means of NMR using Co(II) as a probe. These studies will provide the molecular basis for rational drug design for the purpose of chemotherapy and for design of metal complexes for the study of DNA structure. A review about the structure and function of metalloantibiotics can be found here.
A Book Chapter on NMR of Paramagnetic
Species
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.
(V) Collaborations
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).
USF Summer Program on BioMedical and Life Science for High School Students
CHM2030 General, Organic, and Biological Chemistry: Course information
Co(II)-bacitracin complex
determined by means of NMR
Molecular modling of Pyrococcus POP (green)
on porcine POP (red)
Other than science
What about crayfish outside the lab? (Hmm!)
Anything else, like pets or flowers? (Tell me!)
For questions about the graduate research in bioinorganic chemistry at USF
Email Dr. Li-June Ming at: ming@chuma.cas.usf.edu
Updated Spring, 2001