PROTEOLYSIS, PROTEIN DEGRADATION AND TURNOVER

PROTEIN SYNTHESIS OVERVIEW

PROTEOLYSIS

LIMITED PROTEOLYSIS

Peptide bond cleavage by specific enzymes = proteases.

Limited cleaving of peptides.

New protein product new functions.

Classified = posttranslational modification.

PROTEASES

Exopeptidases = cleave near the N- or C-terminus of peptides and proteins.

endopeptidases (proteinases) = cleave internal peptide bonds in peptides and proteins.

PROTEIN DEGRADATION

Several sites on peptide are cleaved. Complete degradation to AA.

Classified = protein turnover

Occurs in several compartments. Ex: Lysosomes - acidified compartment, individual

proteases degrade proteins Cytosol - ubiquitindependent proteasome system

degrades - at neutral pH.

LYSOSOMAL PROTEIN BREAKDOWN

Acidic pH Various hydrolyses (proteases, nucleases..) Significance –

degradation of extra/intracellular fragments Phagocytosed microorganisms Nutrition

Protein uptake: Endocytosis Autophagy Phagocytosis Specific targeting

UBIQUITIN-DEPENDENT PROTEIN BREAKDOWN

Neutral pH ATP-dependent degradation Significance –

Digestion of proteins programmed for quick destruction

Digestion of misfolding Denaturated Abnormal proteins