Mila Jullig - Lecture 1

Question 1

What are the defining features of a protease?

Answer 1

• an enzyme that conducts proteolysis
• hydrolysis of peptide bonds
• a surface/groove that will fit substrates
• one of more amino acid residues actively involved in activation of water molecule to attack peptide bond

Question 2

What different roles do proteases play within the organism? (8)

Answer 2

• protein turnover
• digestion
• activation of inactive preproteins
• signal transduction
• development
• coagulation
• complement activation
• apoptosis

Question 3

What is the specific reaction performed by proteases?

Answer 3

• breaking of the peptide bond through addition of a water molecule

Question 4

What role does water play during proteolysis?

Answer 4

• it is added across the peptide bond, seperating the amino acids

Question 5

What is the difference between a catalytic triad Vs a catalytic dyad?

Answer 5

• Triad - active site of a serine protease (Ser, His, Asp)

- Dyad - acitve site of aspartic proteases? (2x Asp) and glutamate proteases (2xGlu)

Question 6

What catalytic groups of proteases are known so far and what is the determining factor for these?

Answer 6

• Serine proteases - covalent - nucleophile is OH of serine side chain
• Cysteine proteases - covalent - nucleophile is thiol group of cysteine side chain
• Threonine proteases - covalent - nucleophile is N-terminal threonine
• Aspartic proteases - non-covalent - nucleophile is water activated by 2xAsp
• Metalloproteases proteases - non-covalent - nucleophile is water activated by 1/2 metal ions (Zn)
• Glutamate proteases - non-covalent - catalytic dyad that activates water
• Aspargine peptide lyases - cleave themselves using Asp as nucleophile. DOESN’T use water

Question 7

What basic feature separates asparagine peptide lyases from all other catalytic groups?

Answer 7

• Does not involve water

- Cleaves itself

Question 8

Why is it necessary to control protease activity within an organism and what levels of control are you aware of?

Answer 8

• Inside cells not all proteins should be degraded, so selectivity is required and the protease should only be active when necessary
• zymogen precursors prevent activity in unsuitable areas
• transcriptional regulation
• translational regulation

Question 9

What is a scissile bond?

Answer 9

• the bond of a substrate that is subject to enzymatic cleavage