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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 a-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, with Dr.
Brian Livingston at the Biology Department of the University on molecular
biology in expression of metalloproteins, with 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, prolyloligopeptidase
(POP) from the hyperthermophilic Archaeon
Pyrococcus furiosus with Dr. Valerie Jody Harwood
(Biology) of the University, 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