Co and post translationational modification of proteins

here the modifications of protein i.e co and post are described .

1. St. THOMAS COLLEGE RUABANDHA TOPIC - CO AND POST TRANSLATIONAL MODIFICATION OF PROTEINS . ( PAPER:6 MOLECULAR BIOLOGY ) GUIDED BY : SUBMITTED BY : Dr. SHUBHA THAKUR V. SUKIRTI M.Sc. II SEM BIOTECHNOLOGY YEAR- 2016-17

2. SYNOPSIS 1 . INTRODUCTION 2. OVER VIEW OF TRANSLATION CO- TRANSLATIONAL MODIFICATIONS POST TRANSLATIONAL MODIFICATIONS REGULATION OF TRANSLATION PROTEIN FOLDING AND PROCESSING ENZYMES THAT CATALYZE PROTEIN FOLDING MYRISTOYLATION PRENYLATION PALMITOYLATION PROTEIN CLEAVAGE GLYCOSYLATION IN ER ADDITION OF GPI ANCHORS GLYCO PROTEIN FOLDING ATTACHMENT OF LIPIDS PHOSPHORYLATION UBIQUNATION LYSOSOMAL PROTEOLYSIS .

3. INTRODUCTION

4. OVER VIEW OF TRANSLATION TRANSLATION : m -RNA is decoded by the ribosome to produce a polypeptide chain or a protein. Three stages of Translation :- INITIATION. ELONGATION. TERMINATION.

5. CO -TRANSLATIONAL MODIFICATIONS

6. 1. REGULATION OF TRANSLATION i)Translational regulation of Ferritin protein:- - Supply of iron. m- RNA contains Iron response element (IRE). Adequate iron – translation proceeds . Iron scarce – IRP (Iron regulatory Protein) binds to IRE, blocking translation.

7. ii) Regulation of translation by mi-RNA:- Micro RNAs ( mi-RNA s) -20- 25 bases , double stranded , regulates gene expression . Translational regulation is mediated by the association of mi-RNA with RISC (protein complex) and unwinding of m-RNA strands. m i-RNA targets RISC to homologous m-RNA leading :- m -RNA cleavage. Repression of translation.

8. iii )Translational regulation by phosphorylation of eIF2 and eIF2B:- *ADEQUATE GROWTH FACTOR SUPPLY : Active eIF2 complexed with GTP escorts initiator methionyl t-RNA to the ribosome. eIF2 is then released from ribosome in an inactive GDP form. eIF2 must be reactivated by eIF2B, which stimulates the exchange of GTP for the bound GDP & translation proceeds.

9. *STRESS OR GROWTH FACTOR STARVATION Cells are stressed or starved of growth factors – Translation inhibited. Regulatory protein kinase phosphorylate either eIF2 or eIF2B. These phosphorylations block the exchange of GTP for GDP & eIF2 cannot be regenerated.

10. 2) PROTEIN FOLDING IN ER Proteins translocated across the ER membrane as unfolded polypeptide chains. Polypeptides fold into 3-D conformations by Chaperons BiP ( helps in folding of protein) , binds to polypeptide chains. It facilitates protein folding and assembly within ER. Correctly assembled proteins- released from BiP for the transport. Improper proteins are targets for degradation.

11. 3) ENZYMES CATALYZING PROTEIN FOLDING :- * Formation of di sulfide bonds :- PDI (Protein Disulfide Isomerase ) catalyzes the breakage and rejoining of di sulfide bonds . The PDI forms a disulfide bond with a cysteine residue and exchanges its paired disulfide with another cysteine residue. In this the PDI catalyzes the conversion of 2 incorrect disulfide bond (1-2 & 3-4) to correct pairing. (1-3 & 2-4).

12. 4) MYRISTOYLATION :- A fatty acid like myristic acid is attached to the N- terminal glycine residue of growing polypeptide chain called N- myristoylation . Methionine is removed by proteolysis before fatty acid addition leaving the glycine. Myristic acid is added to the polypeptide chain.

13. 5) PRENYLATION :- Prenyl groups are attached to the sulfur atoms in side chains of cysteine residues near C- terminus. Ras proteins terminate with the cysteine followed by two aliphatic amino acids (A) and (X) at C-terminus. 1 st addition of farnesyl group to cysteine ( farnesylation ). 2 nd removal of three C terminus amino acids. 3 rd methyl group is added to cysteine ( methylation ) at C terminus.

14. 6)PALMITOYLATION : - Addition of palmitic acid ( Palmitoylation) i.e. a fatty acid type of 16-C atoms) to sulfur atoms of internal cysteine residues.

15. POST TRANSLATIONAL MODIFICATIONS

16. PROTEIN CLEAVAGE :- Proteolysis (cleavage of poly peptide chain) is important for maturation of proteins. Signal sequence target the translocation of polypeptide chains into the ER. The signal sequence at the amino terminus of polypeptide chain inserts into a membrane channel. Signal sequence is cleaved by the signal peptidase .

17. 2) GLYCOSYLATION :- Proteins glycosylated on asparagine residues ( N- linked glycosylation ). Oligosaccharide is assembled with ER on dolicol phosphate. Oligosaccharides of 14 residues i.e. two N-acetyl glucosamine , three glucose and nine mannose attach to asparagine residue. Glucose residues removed by two enzymes and modified in Golgi apparatus.

18. 3)ADDITION OF GPI ANCHORS:- GPI ( Glycosylphosphatidylinositol ) contains two fatty acid chains , an oligosaccharide consisting of inositol and ethanolamine. GPI assembled to ER and added to polypeptide by C terminal membrane spanning region. It is cleaved and new C terminal is joined to NH2 of ethanolamine leaving the protein attached to membrane .

19. 4) UBIQUNATION Ubiquitin is first activated by the enzyme E1 . Activated ubiquitin is transferred to E2. (other enzyme) Ubiquitin ligase E3 associates with E2 and transferred to the target protein. Multiple ubiquitins are added & poly ubiquitinated proteins are degraded by proteasome . Ubiquitin is released & degradation proteins require energy in the form of ATP.

20. REFERENCES :- Geoffrey M. Cooper, Robert E. Hausman. THE CELL-A MOLECULAR APPROACH.(2007), 4 TH Edition. Botson University. Page no. 319-348. and 398-414. https://en.m.wikipedia.org/wiki/post-translational_modification.

21. THANK YOU..