Zachara_glycobiology Flashcards
what are three essential properties of glycans
They are hydrophilic, hydrated, and often negatively charged
name three glycoconjugates in vertebrates
glycoproteins, glycolipids, and proteoglycans
what are 9 most common monosaccharide building blocks
glucose, galactose, GalNAc, GlcNAc, mannose, fucose, xylose, sialic acid, GlcA, IdoA
two other names for carbohydrates
glycans, sugars
a non-carbohydrate moiety
aglycone, covalently linked to the glycone
humans use glycolipids built exclusively on…
sphingosine, aka glycophingolipids
glycosaminoglycans
long repeating charged disaccharides that when linked to proteins become proteoglycans
a glycosaminoglycan that is rarely found bound to proteins
hyaluronan
a protein covalently modified by 1+ carbs
glycoprotein
glycocalyx
dense, sugary coat of cells/tissues
3 key roles of surface glycoproteins
cell adhesion, self/non-self recognition, pathogen invasion
the carbon in sugars which undergoes nucleophilic attack to become circularized
carbon 1 , or the anomeric carbon
T/F. All common monosaccharides in vertebrates have the same chirality - dextrarotatory (D) configuration
True
3 common modifications of sugar hydroxyl groups
sulfate, phosphate, or acetyl groups
difference between glucose and galactose
one single position of a bond at carbon 4
name 4 features which contribute to polysaccharide diversity
linear vs branched structure, alpha or beta configuration of anomeric carbon, aglycone attachment, and linkage position of each monomer to the next sugar
where do monosaccharides come from (3)
diet, salvage from degraded glycans, or derived from other sugars
two classes of sugar transporters
facilitated diffusion (GLUT) and energy dependent
how are carbohydrates added to nucleotides
through high energy phosphate bond, generate ATP analog. typical conjugation partners are UDP-, GDP-, and CDP
where are glycoconjugates synthesized
ER and golgi, sugar nucleotides pulled in from the cytoplasm by transporters
class of enzymes which catalize glycoconjugation
glycosyltransferases
these two residues terminate most glycoprotein and glycolipid glycons
fucose and sialic acid
influenza surface proteins and their connection to glycans
hemagglutinin, initiates flu infection by binding to cell-surface sialic acids to keep newly made virus from sticking to it, neuraminidase removes sialic acids on soluble mucins that would prevent cell-surface binding of invading virus
how does a cell get rid of unwanted extracellular glycoproteins and proteoglycans (2)
either shed from cell surface, or internalized and degraded in the lysosome
how are glycosphingolipids classed?
based on first sugar added to sphingosine - either galactose or glucose
two ways glycolipids mediate cell-cell interactions
either through binding to complementary molecules on opposing plasma membranes (trans) or modulating activities of proteins in same plasma membrane (cis)
myelin
insulator that allows for rapid nerve conduction
N-linked glycans
glycan linked to protein through an amide bond to an asparagine residue
sequence motif of N-linked glycan
Asn-Xaa-Ser/Thr (Xaa is any AA but proline)
O-linked glycans
glycan linked to protein through hydroxyl on serine/threonine residues (but also sometimes proline, lysine or tyrosine)
GPI anchors
lipid linked to protein through glycan intermediate, way to anchor proteins to the plasma membrane
N-glycan core sugar sequence
Man3GlcNAc2Asn
three types of N-glycans
oligomannose, complex, hybrid
14-sugar glycan transferred to proteins during translation
precurser dolichol phosphate
mucin-type o-glycans
shield epithelial surfaces from physical/chemical damage and protect against pathogen infections. huge proteins, more than 50% sugar by weight. attract water and form gels
congenital muscular dystrophies linked to mutations in this biosynthetic pathway
O-mannosylation- mannose modification of certain proteins improves their solubility and trafficking to cell surface (ex alpha-dystroglycan, glycoprotein connecting ECM to cytoskeleton in many tissues)
two functions of glycan binding proteins
mediating cell adhesion and regulating signaling
two groups of GBPs
lectins and glycosaminoglycan binding proteins
selectin role in inflammation and injury
injury increases expression of selectins, which slow down leukocyte circulation and mediate rolling and chemotaxis into tissue to migrate towards the site of injury
A, B, O blood type antigens formed by…
sequential action of glycosyltransferases encoded by 3 loci
how is O-GlcNac different than other forms of protein glycosylation
it is adding in an O-linked fashion, but is not further extended - it is instead dynamically added and removed from proteins like how protein phosphorylation is
how is O-GlcNac thought to regulate proteins
can compete with phosphorylation, regulation analagous to phosphorylation regulation
T/F. Glycans dominate cell surfaces
Totally true
how do proteins recognize glycans? (5)
h-bonding, salt-bridges, hydrophobic stacking, calcium coordination, multivalency
how does heparin anticoagulant work
thrombin cleaves fibrinogen to soluble fibrin, which starts to stick together. thrombin then becomes inhibited by antithrombin protease. heparin binds to antithrombin, accelerating inhibition and blocking coagulation
5 forms of protein glycosylation
N-linked, O-linked, GPI-anchors, C-mannosylation, and phosphoglycosylation
4 ways glycans can change a glycoconjugate
alter structure, localization, turnover, and interactions
