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lecture6_large - Protein Structure and Function Lecture 6:...

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1 Protein Structure and Function Lecture 6: Post-translational modification Handouts Chemistry happens Proteins are molecules. Everything you learned (and forgot) about chemistry can be applied to proteins. Proteins undergo chemical reactions. ¾ Hydrolysis, ester formation, amide formation, oxidation- reduction, nucleophilic attack, etc.
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2 Common post-translational modifications Proteolytic cleavage Glycosylation Disulfide bond formation Hydroxylation Phosphorylation Amidation Acetylation Methylation Ubiquitination + many more Proteolytic cleavage Some proteins/polypeptides are activated by snipping off part of the chain (proproteins) ¾ Proinsulin to insulin ¾ Proenzymes to enzymes, e.g., chymotrypsinogen S S S S S S H 2 N COOH S S S S S S H 2 N COOH H 2 N COOH Cleave Cleave Proinsulin Insulin
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3 Cysteine protease zymogens Cathepsin L, K, S, … Cathepsin B Papain Cathepsin C Cathepsin X Cathepsin F 205 aa 250 aa 105 aa 95 aa 215 aa 235 aa 215 aa 62 aa 242 aa 215 aa 38aa 242 aa Procathepsin L
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4 Proteolytic cleavage (preproteins) Preproteins, contains peptide fragment used for targeting Signal peptides ¾ Leader sequences to direct transport of the protein to proper location in the cell ¾ The sequence is often clipped off when it reaches its destination Translocation across bacterial plasma membrane Stryer, Biochemistry
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5 Glycosylation Most common form of postranslational modification ¾ But much less common in bacteria ¾ Takes place in Golgi, ER and extracellular surfaces O -glycosylation ¾ Ser, Thr, hydroxy-lysine N -glycosylation
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lecture6_large - Protein Structure and Function Lecture 6:...

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