Lecture 13- Protein decoration by glycosylation and lipidation Flashcards
n vs o glycosylation
N- sugar bound to the nitrogen, on asparagine residues
O- binds to the oxygen on serine and threonine residues, tend to be more diverse, even at the core
enzyme involved in glycan production
glycosyl transferases, which are integral membrane proteins
ways energy can be gathered for the glycosyl transfer reaction
free NDPs becomign NMPs, dolichol phosphate formation from a NDP reacting with dolichol phosphate on the membrane
how can monosaccharide donors be manipulated from one side of a membrane to another
antiporter proteins of flippases
2 ways to catalyse protein glycosylation
building a glycan directly on the protein via an ‘assembly line’- continually attaching sugars
building an oligosaccharide precursor onto dolichol-phosphate in the membrane, can then transfer this via an oligosaccharide transferase
what is the point of glycan trimming
acts as a timer for protein folding- once the mannose starts to degrade, proteins begin to get marked for degradation- also helps ‘fine tune’ the PTM in the Golgi
core N glycan structure
3 mannose and 2 glucosamine
examples of an o glycan and its function
fucose- used in cell-cell recognition in drosophila brains
GalNac- exist at the hinge of antibodies, have a stabilising effect
what is glypiation and how are they attached
type of lipidation, anchors proteins to a cell membrane via a GPI anchor at the C terminus
how does GPI anchor proteins
GPI signal at the C terminus is added to the precursor, catalysed by GPIT, leading to the signal being removed and anchoring process occuring
steps in GPI anchor synthesis
10 steps total, involving addition of inositol and GlcNac
example of a GPI regulated protein
matrix merallo-protease, regulates the ECM from outside of the cell
examples of other lipidations
palmitoylation
myrsistolyation
prenylation
Palmitoylation- where on the protein, catalysed by, example of their use
Cys residues
transmembrane PATs (lipid droplet proteins)
reversible PTM so can be used to control transport of other proteins across the Golgi membrane depending on protein need- helps to concentrate cargo at the ‘edge’ of the Golgi
Myristylation- where on the protein, catalysed by, example of their use
N-terminal glycine
N-myristoyl transferases (NMT)
can be co- or post-translational depending on why the Gly is exposed
important in apopotosis- added during cleavage of BID, which can associate with the mitochondrial membrane and eventually trigger cytochrome C release and apoptosis
