Post-translational modifications of proteins : Acetylcholinesterase as a model system

1. Post-translational modifications of proteins : Acetylcholinesterase as a model system 화학부 단백질 유전체학 연구실 이 형 호

2. Contents • Introduction • Amino acid modification • Bacterial toxins and post-translational modifications • Glycosylation • Other lipid modifications • Protein turnover • Limited proteolysis and membrane protein secretases • Proteolysis of the amyloid precursor protein(APP) • and Alzheimer’s disease • 9. Post- translational modification of Ache : • its physiological role and significance

3. Introduction

4. 2. Amino acid modifications # N-terminal protein modifications Removal of N-terminal methionyl residue (by methionine amino-peptidase ) : occurs when second residue is one of the smallest amino acid → correlate with stability, turnover of protein, function

5. N-termial의 methionine을 • Cleavage하는 것은 중요함 • (bacteria와 yeast에서 • gene을 deletion했을때 치사) • Acetylation • Methyation • Phosphorylation

6. # C-terminal protein modification : less diverse than N-terminal but include amidation and glycosyl-phosphatidylinositol(GPI) anchor addition # Nonenzymic modification ex) vasodilator (NO) : haemoglobin과 myoglobin의 cystein residue에 binding

7. 3. Bacterial toxins and post-translational modifications Ex) cholera and pertussis toxins : modify G proteins through ADP-robosylation

8. 4. Glycosylation N-linked, O-linked, GPI-linked → glycosylation is not normally a reversible phenomenon and does not play a role in regulation of activity : maintain the solubility of glycoprotein ensure the correct folding of the extracellular domains and stability of the protein against degradation protein targeting and recognition

9. 5. Other lipid modifications Myristoylation, palmitoylation, prenylation Ex) addition of myristic acid : N-term sequence Met-Gly- → after removing of the initiation Met myristate is attached to the glycine residue Many signalling protein are N-myristoylatied : many protein kinase and phosphatases, various G proteins, Ca-binding protein protein etc..

10. 6. Protein turnover Degradation of many cellular protein requires the Covalent addition of ubiquitin as a signal for proteolysis By the proteasome Post-translaional modification : addition of multiple ubiquitin → ubiquitin-activating enzyme ubiquitin-conjugating enzyme ubiquitin-protein ligase Many regulatory proteins are degraded by the ubiquitin system

11. 7. Limited proteolysis and membrane protein secretases Limited proteolysis of cell-surface protein are cleaved By the membrane protein secretase like ACE secretase

12. 8. Proteolysis of the amyloid precursor protein (APP) • and Alzheimer’s disease • Intracellular neurofibrillary tangles • Extracellular senile plaques • → abnormal post-translational modification • tau protein : abnormal hyper-phosphorylated form • in the case of the tangles • O-GlcNAc-modified in normal modification

15. 9. Post-translational modification of AChE its physiological role and significance In different species of animals and in various tissues : conserved catalytic domain + variable C-terminal domain (by alternative splicing) Different molecular forms of AChE are characterised by different localisation → Soluble form : plasma, cerebrospinal fluid, venom of snakes GPI-anchored form : surface of blood cells Collagen-tailed form : neuromuscular junction

17. 10. Concluding remarks Knowing the sequence of the human genome is Only a first step towards understanding the complexity Of the protein component expressed in cell Technologies must continue to be developed to Allow analysis of the these modification