生物化学原理教学（杨荣武）Chapter40 Post-translational processing and protein targeting and sorting.pptVIP

Outline Post-translational processing Cleavage of polypeptides Addition of aa to N-terminal Splicing of protein Chemical modification of individual aa Binding of cofactors Protein oligomerization Protein folding Targeting and sorting of proteins Signal hypothesis Co-translational targeting sorting Post-translational targeting sorting Post-Translational Processing During translation, about 30-40 polypeptide residues are relatively protected by the ribosome. ? Once the polypeptide chain emerges from the ribosome it starts to fold and can be subject to post-translational modifications. Why post-translational processing? 1) adds functionality 2) effects targeting 3) regulates activity 4) increases mechanical strength 5) changes recognition Covalent modification Acetylation, Lipidation, Amidation, Disulfide cross-linking, Phosphorylation, Glycosylation Methylation Sulfation, Vitamin K-Dependent Modifications( γ-carboxylation) , Vitamin C-Dependent Modifications (hydroxylation) Ubiquitination and sumoylation Protein Splicing Protein splicing is defined as the excision of an intervening sequence (the Intein) from a protein precursor and the concomitant ligation of the flanking protein fragments (the Extein) to form a mature host protein and the free intein Inteins as Mobile Genetic Elements: Homing Endonuclease Activity Examples: Totals:48 different species and strains.7 eukaryotes (3 in unicellular organisms, 3 in plastids and 1 in a viruse),24 bacteria (3 in bacterio- and pro- phages),17 archaea. 128 inteins 236 types of protein family hosts 5.111 separate proteins with inteins:94 with a single intein, 2 pairs each with one split intein 2, 12 with 2 inteins and 3 with 3 Mechanism- a self-catalyzed process Protein Folding Primary structure determines 3D struture Proper and fast Folding of most proteins needs to be assisted by molecular chaperones-HSP70 Chaperonins Folding of some proteins requires protein disulfide isomerase