Preferred Membrane Orientation of Dolichol (left) and Dolichylphosphate (right) in Model Phospholipid Membrane:
Many glycosyltransferases contain contact amino acids within a transmembrane spanning domain that constitute a specific binding motif for interacting with dolichol and dolichylphosphate. These binding complexes may be important in biosynthetic and translocation processes that ferry glycoconjugates across cell membranes. The molecular details of this aspect of glycobiology is not understood in any biological system."
Molecular medicine specializes in glycobiology, membrane chemistry and cancer metastasis. We study three overlapping problems in molecular medicine that focuses on glycobiology, membrane chemistry and cancer metastasis.
A summary of these areas and relevant publications are described below.
I. Glycobiology-The Polysialic Acid Glycotope: Structure, Function, Synthesis and Glycopathology.
The landscape of the cell surface of normal and cancer cells is decorated with a bewildering array of informational-rich sugar molecules, usually attached to proteins (glycoproteins) and lipids (glycolipids). Surface expression of many of these complex sugars change dramatically during the developmental life of a cell and with the onset of cancer. Importantly, these sugars carry specific information that tell cells how to behave at different stages in their life cycle, when to detach, for example, and move to different locations within the body. They also signal to the cell when to stop dividing and become adherent. A specific example of one class of these surface carbohydrates in “polysialic acid” (polySia), the focus molecule for many of our studies. The references below summarize some of our studies.
II. Role of the Polysialic Glycotope in Human Cancer Metastasis.
The a2,8-ketosidically linked polySia on neural cell adhesion molecules (N-CAMs) is and oncodevelopmental, tumor-associated carbohydrate antigen. PolySia is an anti-adhesive glycotope that decreases N-CAM dependent cell adhesion in a variety of tissues. Based on correlative studies, we have shown that surface expression of polySia is positively correlated with increased metastasis in a number of human cancers. As such, polySia is postulated to be a metastatic factor than may help some tumors detach, invade and colonize distant sites, particularly brain. Two key mammalian CMP-Sia:a2,8-polysialyltransferase genes, designated PST and STX, have been cloned and shown to catalyze the polysialylation of N-CAM. One discovery-based aim of our studies seeks to determine the extent to which human cancers, including head and neck, breast, prostate, melanoma, and neuroblastomas overexpress polySia on their cell surfaces and to correlate this expression with their malignant potential and patient outcome. One such study is currently being carried out in collaboration with Professor Paul J. Donald, Director of the Skull Base Surgery Program, Department of Otolaryngology, UC Davis Medical Center.
III. NMR Studies on the Preferred Membrane Orientation of Polyisoprenols (Dolichol) and How the Binding Complex of Polyisoprenol Recognition Peptides and Polyisoprenols Can Modulate Membrane Structure
A problem of fundamental importance in glycobiology is how membrane-bound hydrophilic glycoconjugates are translocated across hydrophobic membranes. A number of our studies over the years have addressed the unresolved problem of how sugar chains attached to the polyisoprenol (PI) glycosyl carrier lipids, dolichylphosphate and undecapreylphosphate, are ferried across cell membranes. We have employed a combination of 1H- and 31P NMR spectroscopy, and energy minimized molecular modeling studies, to determine the preferred orientation of PIs in model phospholipids membranes. We have also shown how transmembrane glycosyltranferases that contain a PI recognition sequences (PIRS) uses this motif to mediate their binding to the PIs. Evidence in support of the hypothesis that a PI:PIRS binding complex may have the potential of forming a membrane channel that could potentially facilitate glycoconjugate translocation is also reviewed in our publications below.
Sevigny, M. B., Zhang, L., Hatfield, S. D. and Troy, F. A. Biochemical Studies to Elucidate the Molecular Mechanisms of α2,8-Linked Polysialylation. In: Sialobiuology and Other Novel forms of Glycosylation (Inoue, Y., Lee, Y. C., and Troy, F.A. eds) Gakushin Publ. Co., Osaka, Japan. 1999. pg.171-182.
Angata, T., Nakata, D., Matsuda, T., Kitajima, K., and Troy, F. A. Biosynthesis of KDN (2-keto-3-deoxy-D-glycero-D-galacto-nononic acid). Identification and Characterization of a KDN-9-phosphate Synthetase Activity from Trout Testis. J. Biol. Chem. 1999. 274; 22949-22956.
Sato, C., Fukuoka, H., Ohta, K., Matsuda, T., Koshino, R., Kobayashi, K., Troy, F. A.,and Kitajima, K. Frequent Occurrence of Pre-existing (2,8-Linked Disialic and Oligosialic Acid with Chain Lengths Up to 7 Sia Residues in Mammalian Brain Glycoproteins. J. Biol. Chem. 2000. 275;15422-15431. [Appendix VI].
Zhou, G-P. and Troy II, F.A. Characterization by NMR and Molecular Modeling of the Binding of Polyisoprenols (PI) and Polyisoprenyl Recognition Sequence (PIRS) Peptides: Three-dimensional Structure of the Complexes Reveals Sites of Specific Interactions. Glycobiology 2002. 13; 51-71.
Upper division courses
- 192 Internship in Biological Chemistry
- 198 Group Study
- 199 Special Study for Advanced Undergraduates
Professional courses for medical students
- 209 Prostaglandins/Leukotrienes and Related Lipids (offered even years)
- 214 Molecular Medicine
- 217 Molecular Genetics of Fungi (odd years)
- 222 Mechanisms of Translational Control (even years)
- 230 Practical NMR
- 231 Biomedical NMR (same as BPH 231)
- 291 Human Genetics Seminar
- 298 Group Study
- 299 Research
- 410A Molecular and Cell Biology
- 499 Research