Guisen Jiang, M.S., M.D.
Research Assistant Professor
- Master of Biophysics, Beijing Medical University 1981
- M.D. Beijing Medical University, 1968
The explosion of scientific knowledge and rapid development of new technologies create great opportunities but also build great challenges for researchers. To make effective progress scientists have to constantly update their knowledge and adapt to new techniques. Since I switched my career from clinical medicine to research 20 year ago, I had focused on various topics ranging from biophysics, biochemistry, virology, molecular biology, and now to proteomic study. The obscure is obvious, but it is never too older to learn.
My current research is focused on the field of modern mass spectrometry (MS) technology. I have been running the mass spectrometers and had investigated various ways to extend the usefulness of the instrument as well as packing the columns and developing new method for tuning and calibration of mass spectrometer. As a team member, I have helped identified hundreds of proteins from different research subjects. I am working to improve the sensitivity of the instruments in order to increase the efficiency of protein identification as well as protein modification.
In the past, I had been involved in a variety of projects using modern biochemical and biophysical techniques. The principal studies are summarized below:
- Membrane fluidity: Model lipid membrane and cell membrane fluidity was studied by fluorescence spectroscopy and fluorescence polarization methods. These studies demonstrated that membrane fluidity depends on lipid composition. Fluidity is increased when the lymphocytes were malignant (leukemia) and proliferating.
- Fluorescence probe labeling dynamics: The dynamics of labeling cell membrane with DPH was studied by steady-state fluorescence technique as well as mathematical analysis of three-compartment model. These studies demonstrated that the order and packing density of lipids are higher in Ehrlich ascites cell membranes than in cell plasma. The fluorescence probe labeling process reflected molecular diffusion and interaction.
- Lipid polymorphism: Lipid membrane morphology change induced by surfactant and proton was studied by NMR. The results suggested that phosphate residues of phospholipids may interact with surfactant molecules through hydrogen bonds. Transitions of cardiolipin bilayer to hexagonal II phase may facilitate proton transmembrane transport.
- Kinetics of assembly of fibrin gel: Fibrinogen was labeled with fluorescein isothiocyanate (FITC) and aminoazobenzene-isothiocyanate (ABITC). The labeled fibrinogen remained its ability to form fibrin. The diffusion coefficient of the labeled molecule was studied during fibrin formation by laser holographic relaxation spectroscopy.
- Toxin protein transmembrane: Intoxication of cells by diphtheria toxin requires passage of fragment A through the membrane of an acidified endosome. Our studies demonstrated that low pH induces a conformational change in the toxin protein. Exposure of hydrophobic domain of the protein facilitates its insertion into the lipid membrane. Both fragment B and A of the toxin can insert into lipid membrane at low pH. Fragment A insertion is reversible when the pH is returned to neutral. This is a clue for its translocation: low pH induces its insertion into endosomal membranes; neutral pH in cytosol makes it released from the endosome.
- Mouse Hepatitis Virus (MHV) receptor purification and characterization : Infection of cells by viruses begins with the attachment of the virus to a specific receptor on the cell surface. I purified the MHV receptor glycoprotein from mouse liver and obtained its N-terminal amino acid sequence. The sequence revealed strong homology to the human carcinoembryonic antigen (CEA) family, and facilitated the cloning of the receptor gene. I also used the purified receptor protein to immunize rabbits. The polyclonal rabbit anti-receptor serum binds to the MHV receptor on the cell surface and protects the cells from MHV infection.
- The rrg (ras recession gene), a regulator of ras expression, encodes lysyl oxidase: To study the lysyl oxidase, I purified the human 3H-lysine-tropoelastin as the enzyme substrate by protein engineering and established the enzyme assay process.
- Under the GLP or GMP regulation, I had done the purification and characterization of the HIV582- galactosidase (HIV gp-120 fragment fused with galactosidase), Characterization of the recombinant exotoxin A of Pseudomonas aeruginosa, and purification and characterization of Mucoid exopolysaccharide (MEP) vaccine from Pseudomonas fermentation culture.
- Melanopsin identification, cloning and expression: Xenopus melanophores response to light by redistribution of pigment. Working with Dr. Rollag and Dr. Provencio, we identified an opsin-like protein and had successfully cloned the gene from the cell. The deduced amino acid sequence shares great homology with cephalopod opsins, it was called melanopsin. We further cloned the melanopsin from chicken, mouse, to human. Melanopsin was located in retinal ganglion cells that are intrinsically photosensitive and projected to the hypothalamic suprachiasmatic nucleus, the site of the primary circadian pacemaker. This study suggests that melanopsin may play a role in the photic regulation of mammalian circadian rhythms.