Post-translational modifications

Question 1

Types

Answer 1

• Covalent modifications that occur after translation
  
  • Proteolytic cleavage
  • Addition of functional groups

Question 2

Protein PTM

Answer 2

• Most eukaryotic proteins are modified by post-translational
  modifications
• Increase functional diversity of proteins
• Many PTMs are dynamic, enabling cells and organisms to respond
  rapidly to changes in their environments
• Aberrant PTMs are markers of cellular stress or malfunction and are
  implicated in disease
• Addition of small chemical groups and complex biomolecules to side
  chains
• Includes:
• Glycosylation
• Ubiquitination
• Lipidation
• Phosphorylation
• Acetylation
• Methylation Covalent modification of a nucleophilic
  amino acid side chain by an
  electrophilic fragment of a cosubstrate

Question 3

Phosphorylation

Answer 3

• Reversible enzymatic reaction
• Covalent attachment of a charged
  phosphate group to the side chain of a
  Y, S, or T
• Enzymes dedicated to protein
  phosphorylation are among the largest
  class of PTM enzymes
• Kinases phosphorylate
• Phosphatases dephosphorylate

REGULATION:
Cellular localization of a POI with kinases and phosphatases
* Scaffolding proteins – bring POI and kinase/phosphatase
into proximity
* Feedback loops (self-regulation)
* Reversibility

Question 4

N-Acetylation

Answer 4

• Covalent PTM
• Acetyl group is transferred either to the alpha-amino group of terminal
  residues or to the epsilon-amino group of lysines at specific sites
• Reversible

Question 5

N-Methylation

Answer 5

• Lys NH 2 groups can be progressively mono-, di-, or trimethylated
• Arg residues can be both mono- and dimethylated
• Size and hydrophobicity differences between monomethyl and trimethyl side chains enable selective recruitment of proteins involved in transcriptional
  control.

Question 6

How do we study PTMs?

Answer 6

• Antibody-based analyses
• Mass spec-based analyses
• Treating a POI with a kinase or phosphatase
• Radiolabeling phosphoproteins (P-32)
• Site-directed mutagenesis to create mimetics or knock out sites of
  modification
  • Phosphomimetic: mutation to aspartic acid
  • Phospho KO: mutation to alanine