BCHM - Functions and Dysfunctions of Protein Processing

Question 1

In the cytoplasmic pathway of protein sorting, where are the proteins destined for?

Answer 1

Cytosol, mitochondria, nucleus, and peroxisome

Question 2

In the cytoplasmic pathway of protein sorting, where does protein synthesis begin and end?

Answer 2

Begins and ends on the free ribosomes of the cytoplasm

Question 3

In the secretory pathway of protein sorting, where are the proteins destined for?

Answer 3

Endoplasmic Reticulum, lysosomes, plasma membrane, or secretion

Question 4

In the secretory pathway of protein sorting, where does translation begin and end?

Answer 4

Begins on free ribosomes, but ends in ribosomes sent to the ER

Proteins undergo second part of synthesis in the ER

Have ER targeting signal sequences on first 20 amino acids (N-terminus)

Question 5

In the cytoplasmic pathway, what signal moves the protein to the cytoplasm?

Answer 5

No signal required

Question 6

In the cytoplasmic pathway, what signal moves proteins into the mitochondria?

Answer 6

N-terminal hydrophobic alpha-helix

Question 6

In the cytoplasmic pathway, what signal moves proteins into the mitochondria?

Answer 6

N-terminal hydrophobic alpha-helix

Question 7

In the cytoplasmic pathway, what signal moves the protein into the nucleus?

Answer 7

Lysine and Arganine rich signals

Question 8

In the cytoplasmic pathway, what signal moves the protein into the peroxisome?

Answer 8

Serine, Lysine, Leucine signaling complex

Question 9

In the secretory pathway, what moves the protein into the ER?

Answer 9

KDEL

Lysine, aspartic acid, glutamic acid, and leucine

Question 10

In the secretory pathway, what moves the protein into the cell membrane?

Answer 10

N-terminal apolar signals

Examples include GLUT transporters

Question 11

In the secretory pathway, what moves the protein into the lysosome?

Answer 11

Mannose-6-phosphate

Question 12

In the secretory pathway, what moves the protein into a secretory vesicle for secretion?

Answer 12

Trp-rich domains

Tryptophan

Question 13

During the import of mitochondrial proteins, HSP70 does what?

Answer 13

HSP70 is a chaperone protein that protects the mitochondrial protein from degradation

Question 14

Describe the pathway of mitochondrial protein import

Answer 14

Proteins pass through TOM and then TIM. After that, they enter the matrix, and a peptidase cleaves the signaling sequence, trapping the protein within the mitochondrial matrix

Question 15

Describe the pathway of nuclear protein import

Answer 15

• Proteins pass through nuclear pores
• Small proteins can pass through un-aided, but larger proteins (>40 kDa) require nuclear localization signals
• four continuous basic residues (Lys and Arg)

Question 16

During the secretory pathway, the signal recognition particle does what?

Answer 16

Binds to the ER-targeting signal and the ribosome during translation. It then wraps itself around ribosome-mRNA-peptide complex, tethering it to the ER membrane, thus halting its translation temporarily

Question 17

What is Inclusion Cell Disease?

Answer 17

A disease characterized by a defective or missing GlcNAc phosphotransferase, and enzyme that adds M6P to lysosomal hydrolases.

No M6P tagged on lysosomal proteins

If the enzymes are not phosphorylated, they cannot be sorted into vesicles and delivered to lysosomes

Question 18

Describe the clinical presentation of Inclusion Cell Disease

Answer 18

Failure to thrive, developmental delays, and physical manifestations such as hepatosplenomegaly and defective heart valves.

Death frequently occurs by age 7 due to congestive heart failure or recurrent respiratory tract infections

Question 19

What is the function of chaperone proteins?

Answer 19

To protect large proteins and help fold into proper tertiary structure

Question 20

Which heat-shock protein is ATP-dependent?

Answer 20

HSP60 (a chaperonin - barrel shaped compartment that catalyzes the folding of proteins via ATP)

Question 21

What is the function of proteolytic cleavage?

Answer 21

Converts inactive forms to active enzymes by uncovering active sites

Chymotrypsinogen to its active form, chymotripsin
Trypsinogen to its active form, trypsin

Also converts nascent precursor proteins to mature ones (i.e. proinsulin to insulin)

Question 22

What proteins are glycosylated during glycosylation?

Answer 22

Extracellular proteins (cell surface proteins and plasma proteins)

Question 23

What are the TWO types of glycoproteins involved in glycosylation?

Answer 23

1. O-glycosidic (formed with hydroxyl groups of Ser or Thr)

2. N-glycosidic (formed with asparagine and sometimes glutamine)

Question 24

During acetylation, where are the proteins typically located?

Answer 24

Lysine residues

Question 25

During acetylation, histones are modified where?

Answer 25

N-terminal lysines. This is critical for gene regulation

Question 26

What enzyme catalyzes acetylation? What about deacetylation?

Answer 26

Acetylation is catalyzed by Histone Acetyltransferase (HAT)

Deacetylation is catalyzed by Histone Deacetylase (HDAC)

Question 27

Consequences of protein mis-folding include…

Answer 27

Generation of ROS, increased oxidative stress, disrupted neuronal signaling, disrupted ion homeostasis, calcium disregulation, disruption of energy homeostasis, inflammation, damage organelles, and breaks plasma membrane, leading to death.

Question 28

Define Familial Nuerodegeneration

Answer 28

Mutations that arise in specific genes.

Represents early onset forms of disease

Question 29

Define Sporadic Neurodegeneration

Answer 29

No known cause.

Represents late onset form of the disease, with brain aging being the common denominator

Question 30

What are the symptoms of Parkinson’s Disease?

Answer 30

• rigidity and stiffness of limbs/trunk
• tremors in hands, arms, legs, etc
• slow movement
• difficulties with balance, speech, and coordination

Question 31

What are some of the treatments available for Parkinson’s disease?

Answer 31

Dopamine replacement therapy (levodopa), deep brain stimulation, surgery, and stem cell therapy

PD is the result of the death. of dopamine producing cells, drastically decreasing available dopamine in the brain

Question 32

What is the area of the brain called that produces dopamine?

Answer 32

Substantia nigra

Iron and mitochondria rich area of the brain. In PD, the substantia nigra is excessively diminished.

Question 33

Parkinson’s disease is caused by the aggregation of what protein?

Answer 33

Alpha-synuclein (AS)

AS is a 14 kDa protein that is found in the cytosol and plasma membrane

Question 34

What happens when alpha-synuclein aggregates in PD?

Answer 34

Forms insoluble fibrils that deposit as Lewy bodies in dopaminergic neurons in the substantia nigra

Question 35

What are the signs and symptoms of Alzheimer’s Disease?

Answer 35

• memory loss that disrupts daily life
• confusion with time or place
• difficulty understanding visual images and spatial relationships
• misplacing things
• changes in mood and personality

Question 36

What are the neuropathologic manifestations of Alzheimer’s disease?

Answer 36

Decreased size in memory and language areas of the brain

Question 37

Where on the neuron is plaque found?

Answer 37

Outside the neuron (extracellular)

Question 38

Where on the neuron is tau found?

Answer 38

Inside the neuron (intracellular)

Question 39

What peptide is formed and released that causes AD when misfolded?

Answer 39

Amyloid beta peptide (4.2 kDa) is generated and released into extracellular space.
Misfolded amyloid beta forms soluble oligomers and insoluble plaques

Question 40

What areas of the brain are most affected by Huntington’s Disease?

Answer 40

Basal ganglia and cerebral cortex

Progressive disorder caused by death of brain neurons

Question 41

What three primary aspects of brain function does Huntington’s disease affect?

Answer 41

1. Behavior (psychiatric function)
2. Movement (motor function)
3. Thinking (cognitive function)

Question 42

HD is caused by a mutation in which gene?

Answer 42

Huntingtin gene (HTT) - codes for huntingtin protein

Question 43

Describe the Huntingtin protein

Answer 43

Large protein of 350 kDa localized in cytosol and nucleus

Function unknown, but appears to play important role in brain neurons

Involved in signaling, transport, binding, and protecting neurons from apoptosis

HTT knockout is lethal

Question 44

The HTT gene contains a trinucleotide repeat of what three base pairs?

Answer 44

CAG

Expansion of CAG triplet repeats leads to Huntington’s disease

Question 45

What is the relationship between the number of CAG triplet repeats to the age of onset of Huntington’s disease?

Answer 45

10-35 repeats: normal
40-50 repeats: adult onset
60+ repeats: juvenile onset

Question 46

What amino acid does CAG code for?

Answer 46

CAG codes for glutamine

Polyglutamine repeats in abnormal Huntingtin protein forms intramolecular H-bonds, which eventually misfold and aggregate

Question 47

Describe the neuropathology of Huntington’s disease

Answer 47

Atrophied striatum, basal ganglia, and ventricular dilation

Question 48

What are the signs and symptoms of Amyotropic Lateral Sclerosis (ALS)

Answer 48

Often begins with muscle twitching and weakness in a limb, or slurred speech
Eventually unable to move, speak, eat, and eventually breathe.

ALSO affects nerve cells in the brain and spinal cord, causing loss of muscle control

Question 49

Mutations in what cause ALS?

Answer 49

Mutations in Copper Zinc superoxide dismutase (CuZn SOD)

Question 50

Describe CuZn SOD

Answer 50

Enzyme responsible for dismutation of superoxide anion to hydrogen peroxide

Homodimer of 32.5 kDa

Mutations of SOD cause GAIN OF FUNCTION

Forms ROS and induces oxidative stress