Biology of Sialyl Glycans Part 1: Overview of sialic acids in glycans. Joseph Lau

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1 Biology of Sialyl Glycans Part 1: Overview of sialic acids in glycans Joseph Lau

2 Synopsis Sialicacid modifications on glycans:biology, synthesis, and function Not comprehensive review, but select aspects to illustrate state-of-the-art relevance to health and medicine Part 1: overview of glycan functions and sialic acids Part 2: Network of biosynthesis and sialicacid binding receptors Part 3: Recent advances, unusual new paradigms

3 Extrinsic recognition - from Voet & Voet Biochemistry Pathogen Symbiont Toxin self Receptor-driven interaction between microbe and host

4 Influenza 1917 PANDEMIC Acute respiratory tract infection spread from person-to-person by respiratory droplets. ~ 20,000 deaths and110,000 hospitalizations in U.S. annually. Enveloped, single-stranded RNA virus of family orthomyxoviridae. Typical symptoms are fever, dry cough, sore throat, runny or stuffy nose, headache, muscle aches,and extreme fatigue.

5 Examples of Glycosphingolipid Receptors for Bacterial Toxins Toxin Microorganism Tissue Proposed Receptor Sequence Cholera toxin Vibrio cholerae Small intestine Galβ3GalNAcβ4(NeuAcα3Galβ4GlcβCer (GM1 ganglioside Heat-labile toxin Escherichia coli Intestine Galβ3GalNAcβ4(NeuAcα3Galβ4GlcβCer (GM1 ganglioside Tetanus toxin Clostridium tetani Nerve membrane G 1b gangliosides (G T1b most efficient Botulinum toxin Clostridium botulinum Nerve membrane (+NeuAcα8NeuAcα3Galβ3GalNacβ4 (NeuAcα8NeuAcα3Galβ4GlcβCer Toxin A Clostridium difficile Large intestine GalNAcβ3Galβ4GlcNacβ3Galβ4GlcβCer Shiga toxin Shigella dysenteriae Large intestine Galα4GalβCer or Galα4Galβ4GlcβCer

6 intrinsic recognition - from Voet & Voet Biochemistry self self - Receptor-driven interaction - dependency on where glycans and receptors are expressed

7 Biologic Roles of Glycans Structural/Physical Non-self recognition Self (endogenous recognition 耀 Pathogen Symbiont Toxin self self Questions: 1. What are the physiologic roles of the individual carbohydrate structures? 2. How is their expression regulated?

8 Glycosyltransferases DNA RNA Glycosyltransferases Glycosidases Glycans Function Nucleotide-sugar + -acceptor glycosyltransferase Sugar-O-Acceptor CMP-Sia + Galβ1,4GlcNAc-R ST6Gal I Siaα2,6 Galβ1,4GlcNAc-R Glycosyltransferase Family ** Donor substrate Known genes Fucosyltransferase GDP-Fuc 14 Sialyltransferase CMP-Sia 20 N-Acetylglucosaminyltransferase N-Acetylgalactosaminyltransferase UDP-GlcNAc 34 UDP-GalNAc 24 Galactosyltransferase UDP-Gal 26 Mannosyltransferase GDP-Man 13 ** Not counted: glucosyltransferases, enzymes in GAG synthesis, sulfotransferases, other glycan modifying enzymes, and specialized glycosyltransferases. 131 genes!!!

9 Sialic acids Chair: Haworth*: H H-C-OH H-C-OH H-C-OH H O H 6 C O H-C-C-N C 5 H C H H C C H 4 3 OH H O 1 C-OH 2 OH * Won the Nobel Prize in 1937 for his work in carbohydrate chemistry

10 Biosynthesis of sialic acids NHAc NHAc H 2 C H O 2 C -- O O 3 POH 2 C OH OH O -- O O - 3 POH 2 C CO 2 AcHN AcNH OH OH O UDP UDP-GlcNAc ManNAc ManNAc-6-P Neu5Ac-9-P OH H 2 C AcHN OH OH O CMP - OH CO 2 O - H CO 2 C 2 O - CO 2 H 2 C O O AcHN AcHN Neu5Ac CMP-Neu5Ac Sialo-glyco-conjugate

11 The Sialyltransferases sialic acids Exists only at termini of glycans 20 known sialyltransferase genes, in 4 major sub-groups. ST6GalNAc I ST6GalNAc II ST6GalNAc III ST6GalNAc IV ST6GalNAc V ST6GalNAc VI ST3Gal I ST3Gal II ST3Gal III ST3Gal IV ST3Gal V ST3Gal VI α2,3 ST6Gal I ST6Gal II α2,6 ST8Sia I ST8Sia II ST8Sia III ST8Sia IV ST8Sia V ST8Sia VI α2,8 α2,8 α2,8 α2,3 α2,6 β1,3 β1,4 β1,3/4 Acceptor: GalNAc Gal Gal Sia

12 Two major types of sialic acids in mammals 9 a generic sialic acid α-d-neu5ac LINKAGE TO UNDERLYING SUGAR CHAIN H Which form is this? α-d-neu5gc 4 3 LINKAGE TO UNDERLYING SUGAR CHAIN Carbon Oxygen Nitrogen Hydrogen

13 Neu5Gc Synthesized by conversion from CMP-Neu5Ac by CMP-Neu5Ac hydroxylase (CMAH [-Shaw,L., Schauer,R.(1988 Biol.Chem.Hoppe-Seyler 369: ] Hydroxylation occurs in cytosol [Muchmore EA (1989 J.Biol.Chem.264: ] Human CMAH is mutated and inactive [Chou HH et al (2002 PNAS 99: ] mutation occurred after our last common ancestor with chimpanzees but before origin of present humans est. inactivation time of approx. 2.8 mya. Neu5Gc is major SA in most organs of chimpanzee, yet expression is selectively down in brain. Reasons unknown. Humans have circulatory anti-neu5gc, with avidity as high as antiαgal. [Galili U. (1993 Immunol.Today 14: ; Joziasse D.H. & Oriol R. (1999 BBA Mol.Basis Dis. 1455: ] Potential implications: elevated risk for auto-immune syndromes from Neu5Gc? risk of eating foods with too much Neu5Gc?

14 Examples of reactivity of anti-neu5gc antibody with human tissue sections blood vessels in placental villi breast carcinoma, tumor cells and blood vessel skin and eccrine glands kidney tubules Tangvoranuntakul, Pam et al. (2003 Proc. Natl. Acad. Sci. USA 100, Copyright 2003 by the National Academy of Sciences

15 Prevalence of Neu5Gc in diet Neu5Gc intake if eaten at daily recommended servings: Food: Total micrograms Cod 27 Salmon 810 Tuna 27 Chicken 27 Turkey 27 Duck 27 Milk (cow, 2% 711 Milk (cow, raw 711 Butter 45 Cheese (cow 600 Lamb 4,860 Pork 5,130 Cheese (goat 5,544 Beef 11,610 Beef, lean portion 9,720 Beef fat 10,260

16 Summary Part 1 Overview of biologic functions of glycans What are glycosyltransferases Sialyltransferases and their diversity Sialic acids, biosynthesis and heterogeneity