Fredric A Troy, Ph.D.

Professor Emeritus

4430 Tupper Hall  
Ph: (530) 752-3240 
fatroy@ucdavis.edu

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.

• Daisuki Nakata

1. Nakata D, Zhang L, Troy FA 2nd.
   Molecular basis for polysialylation: A novel polybasic polysialyltransferase domain (PSTD) of 32 amino acids unique to the alpha2,8-polysialyltransferases is essential for polysialylation.
   Glycoconj J. 2006 Jul;23(5-6):423-36.
    
2. Cong X, Czerwieniec G, McJimpsey E, Ahn S, Troy FA, Lebrilla CB.
   Structural relationships in small molecule interactions governing gas-phase enantioselectivity and zwitterionic  formation.
   J Am Soc Mass Spectrom. 2006 Mar;17(3):442-52. Epub 2006 Feb 14.
    
3. Zhou GP, Troy FA 2nd.
   NMR studies on how the binding complex of polyisoprenol recognition sequence peptides and polyisoprenols  can modulate membrane structure.
   Curr Protein Pept Sci. 2005 Oct;6(5):399-411. Review.
    
4. Nakata D, Troy FA 2nd.
   Degree of polymerization (DP) of polysialic acid (polySia) on neural cell adhesion molecules (N-CAMS): development and application of a new strategy to accurately determine the DP of polySia chains on N-CAMS.
   J Biol Chem. 2005 Nov 18;280(46):38305-16. Epub 2005 Sep 19.
    
5. Zhou GP, Troy FA 2nd.
   NMR study of the preferred membrane orientation of polyisoprenols (dolichol) and the impact of their complex  with polyisoprenyl recognition sequence peptides on membrane structure.
   Glycobiology. 2005 Apr;15(4):347-59. Epub 2004 Nov 24. Erratum in: Glycobiology. 2005 May;15(5):13G.
    
6. Zhou GP, Troy FA 2nd.
   Characterization by NMR and molecular modeling of the binding of polyisoprenols and polyisoprenyl recognition sequence peptides: 3D structure of the complexes reveals sites of specific interactions.
   Glycobiology. 2003 Feb;13(2):51-71. Epub 2002 Nov 1.
    
7. Sato C, Fukuoka H, Ohta K, Matsuda T, Koshino R, Kobayashi K, Troy FA 2nd, Kitajima K.
   Frequent occurrence of pre-existing alpha 2-->8-linked disialic and oligosialic acids with chain lengths up to 7 Sia residues in mammalian brain glycoproteins. Prevalence revealed by highly sensitive chemical methods and anti-di-, oligo-, and poly-Sia antibodies specific for defined chain lengths.
   J Biol Chem. 2000 May 19;275(20):15422-31.
    
8. Angata T, Nakata D, Matsuda T, Kitajima K, Troy FA 2nd.
   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 Aug 13;274(33):22949-56.
    
9. Inoue S, Lin SL, Chang T, Wu SH, Yao CW, Chu TY, Troy FA 2nd, Inoue Y.
   Identification of free deaminated sialic acid (2-keto-3-deoxy-D-glycero-D-galacto-nononic acid) in human red blood cells and its elevated expression in fetal cord red blood cells and ovarian cancer cells.
   J Biol Chem. 1998 Oct 16;273(42):27199-204.
    
10. Sevigny MB, Ye J, Kitazume-Kawaguchi S, Troy FA 2nd.
    Developmental expression and characterization of the alpha2,8-polysialyltransferase activity in embryonic chick brain.
    Glycobiology. 1998 Sep;8(9):857-67.