Post Translational Processing. Flashcards
Proteolytic Cleavage
Converts inactive forms to active enzymes by unmasking active site (zymogens like trypsinogen to trypsin). Converts nascent precursor proteins to mature ones (pro insulin to insulin).
Glycoslylation
Extra cellular proteins glycosylated.
Covalently linked to sugar residues in the ER lumen.
O-glycosidic
- formed with hydroxyl groups of Ser and Thr residues.
N-glycosidic
- Always With Asparagine. Precursor sugar transferred from phospho Dolichol
Phosphorylation
Formation of ester bond between phosphate and OH of an amino acid.
Uses activity of serine/threonine kinase.
Regulates enzyme activity and protein function particularly in signaling (also in cell growth, proliferation, differentiation, oncogenesis).
Disulfide bond formation
Inter and intra disulfide bonds stabilize many proteins.
Form between thiol (SH) group of two cysteine residues.
Formation of these bonds occurs in ER lumen.
Facilitated by protein disulfide isomerases.
Acetylation
Proteins typically acetylated on Lysine residues, uses acetyl-CoA as acetyl group donor.
Histones are acetylated and deacetylated on their N-terminal Lysines, critical for gene regulation.
These modifications can be inherited (epigenetics).
HAT - catalyzes histone acetylation
HDAC - catalyzes deacetylation.
Post translational modifications of collagen.
Lysines in collagen modified to form 5-hydroxylysines, further glycosylated with addition of glucose and galactose. Some Lysines delaminates to aldehydes. Some prolines hydroxylated to hydroxyproline.
Ascorbic acid essential for activity of Lysyl and prolyl hydroxlyases.
Defects in lysyl hydroxylases result in skin, bone, and joint disorders such as Ehlers-Danlos Syndrome (only flexible joints, walls of blood vessels, intestines or uterus may rupture), Neville syndrome, Bruck syndrome, Epidermolysis Bullosa Simplex (blisters on skin).
