Post-Translational Modification

Disparity in mRNA and Protein profiles Electrophoresis 18(1997)533-537 Splicing variants In eukaryotic cells, likely 6-8 proteins/gene Post-translational modification 22 different forms of antitrypsin observed in human plasma

Posttranslational Modification What is it ? Addition of groups or deletion of parts to make a finished protein What groups ? How much ? Where ? - methyl - acetyl - glyco - phospho

Posttranslational Modification What purpose ? - targeting (eg. some lipoproteins) - stability (eg. secreted glycoproteins ) - function (eg. surface glycoproteins) - control of activity (eg. clotting factors, caspases) How can we study it ?

Post-Translational Modifications

Post-Translational Modifications

Posttranslational Modification Modification Charge-dependent change Acylation loss of a-amino positive charge Alkylation alteration of a- or e-amino positive group Carboxylmethylation esterification of specific carboxyl group Phoshorylation mainly modify Ser, Thr and Tyr Sulfation mainly modify Tyr Carboxylation bring negative charge Sialyation mainly on Asn, Thr and Ser Proteolytic processing truncation leads to change of pI

Posttranslational Modification Location Modification Nucleus acetylation, phosphorylation Lysosome mannose-6-phosphate labelled N-linked sugar Mitochondria N-formyl acylation Golgi N- and O-linked ologosaccharide, sulfation, palimitoylation ER N-linked oligosaccharide, GPI-anchor Cytosol acetylation, methylation, phosphorylation, Ribosome myristoylation Plasma membrane N- and O-glycosylation, GPI-anchor Extraceullar fluid N- and O-glycosylation, acetylation, phosphorylation Extrallular matrix N- and O-glycosylation, phosphorylation, hydroxylation

Posttranslational Modification Examples: Chromatin Structure/function - acetylation Regulation of mitochondrial processes – phosphorylation Evade immune system – glycosylation Gene regulation – glycosylation Recognition - glycosylation

Protein Glycosylation The most important and complex form of PTM Approx. 1% mammalian genes Early view about carbohydrates (non-specific, static structures) has been challenged Ann. Rev. Biochem. 72(2003)643

Protein Glycosylation Which proteins are decorated with glycans (polysaccharides) ? What are the structures of these glycans? What is their functional significance?

Protein Glycosylation Common in Eukaryotic Proteins

Protein Glycosylation - Biological Significance Oligosaccharides may be a tissue-specific marker Carbohydrates may alter the polarity and solubility Steric interaction between protein and oligosaccharides dictates certain protein 3D structure The bulkiness and negative charge of oligosaccharide chain may protect protein from the attack by proteolytic enzymes

The Sugar Code Carbohydrates as Informational Molecule Information: intracellular targeting of proteins, cell-cell interactions, tissue development, extracellular signals Improved methods for structural analysis Sugar code - The unique complex structure of oligosaccharide on glycoprotein read by protein

Lectins carbohydrate-binding proteins Lectins read sugar code and mediate many biological processes : [1] Cell-cell recognition [2] Signaling [3] Adhesion [4] Intracellular targeting of newly synthesized proteins