BB4 Protein Modification Flashcards
Forms of modification
- acetylation
- hydroxylation
- glycosylation
- phosphorylation
Protein modification
- the modification of selected residues in a polypeptide
* not as a component as synthesis
Acetylation
- modifies N-terminal amino acid
- involves Acetyl CoA
- only eukaryotes, not prokaryotes
- not in mito or chloro
- stops other proteins from breaking that protein apart
Hydroxylation
• addition of an OH group to the side chain of specific amino acids in a protein
Amino acids involved in hydroxylation
- proline
* lysine
Essential component of collagen
- hydroxyproline
- hydrogen bonding within the collagen fiber
- structural stability
Repeating unit in collagen
Gly—Xaa—Yaa
• 4-Hyp only in 3rd position
4-Hyp
- formed by enzyme prolyl hydroxylase
* requires ascorbic acid / vitamin c
Glycolysation
- the attachment of sugar molecules to specific amino acids in a polypeptide chain
- only eukaryotes, not prokaryotes
2 forms of glycolysation
- N-Glycolysation
* O-Glycolysation
N-Glycolysation
• sugars attached to the NITROGEN in Asparagine (N)
N-Glycolysation sequence
Asn—Xaa—Ser or Asn—Xaa—Thr
•Xaa not proline
O-Glycolysation
sugars are attached to the OXYGEN in the side chain of the amino acids
• Serine
• Threonine
•no characteristic sequence pattern
Phosphorylation
- attachment of a phosphoryl group to the side chains of specific amino acids in a protein
- most common
Phosphorylation occurs on the side chain OXYGEN atoms of
- Threonine
- Serine
- Tyrosine
Phosphoryl attached to amino acid by enzyme…
protein kinase
Phosphoryl removed from amino acid by enzyme…
protein phosphatases
Cleaving of peptide bonds performed by proteins…
proteases
make-break-recycle to make new
Types of proteases
• Carboxypeptidase A
• Chymotrypsin
• HIV Protease
all active site dependent
Carboxypeptidase (function)
cleaves off the last C-Terminal residue from a polypeptide chain
• works best with aromatic or bulky aliphatic residue
Carboxypeptidase A is a member of the
- metalloproteases
* metal ion at active site - zinc
Chymotrypsin (function)
cleaves peptide bonds on the carboxyl side of aromatic or large hydrophobic residues
• find hydrophobic areas when protein being broken up anyway
Chymotrypsin is a member of the
•Serine Protease family
HIV protease is a member of the…
- Aspartic Protease family
* 2 aspartate residues central to the active site
HIV protease (function)
- cleave itself out of chain protein (from genetic material of virus)
- then cleaves out remaining proteins of the virus
- critical to viral replication, HIV protease inhibitors
Reason why proteins are synthesized as longer chains than native chain
- added sequence directs a protein to specific compartments within a cell
- longer chains assists folding correctly
- longer chain renders protein inactive
Protein Kinase A recognizes
Arg-Arg-small-Ser-Large hydrophobic
Arg-Arg-small-Thr-Large hydrophobic
