Lecture 24 Mgm Protein Targeting

Front 1

Where are polyribosomes located?

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Back 1

free in the cytosol and attached to rough ER

Front 2

What is the destination of proteins made on the rough ER?

Back 2

secreted out of cell

part of cell membrane

Front 3

Protein secretion is _______ and coordinated by _____

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Back 3

Protein secretion is cotranslational and coordinated by SRP

SRP= signal recognition particle

Front 4

What does the Signal recognition particle(SRP) do?

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Back 4

SRP recognizes the signal peptide, temporarily blocks chain elongation by binding to P site, brings protein to ER by recognizing SRP receptor and elongation resumes extruded into the ER

Front 5

How does SRP recognize the signal peptide?

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Back 5

protein has on Nterminus start AUG and then sequence of hydrophobic amino acids (approx 24)--> this is the signal that gets recognized by the SRP

Front 6

what are additional sequences that ship proteins to certain locations after being sent to the ER?

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Back 6

ER membrane - halt (stop-transfer) eg KDEL

Golgi apparatus membrane - unknown

Plasma Membrane -default
Secretion - default

Lysosomal enzyme - mannose 6-phophate attachment

Front 7

What is I-cell Disease caused by? and what does it cause?

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Back 7

I cell disease (inclusion bodies in cells) is due to genetic defect in adding mannose 6-phosphate to the enzymes. This leads to failure of the enzyme to target lysosomes.

Front 8

Where do proteins get sent if they are made in the cytosol?

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Back 8

Stay in Cytosol

Sent to
Nucleus - have nuclear localization signal (basic) importins/RAN proteins

Peroxizomes - peroxizomal targeting sequences / PTS receptors

Mitochondria - N terminal leader (20-80 basic aa's) translocation complexes

Front 9

Where are proteins that are sent to the nucleus made? What helps them to get there?

Back 9

The proteins are made in the cytosol

Have a nuclear localization signal (NLS) that is basic

Imortins/ Ran proteins help bring them into the nucleus

Front 10

Where do proteins that are shipped to the mitochondria get made?

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Back 10

in the cytosol

Have an Nterminus (20-80 basic aa's) translocation complexes

Front 11

What is Zellweger syndrome?

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Back 11

genetic disease from mutations in genes required for peroxisome targeting or function

Front 12

What type of proteins does the mitochondria make itself?

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Back 12

makes about 13 proteins chiefly of the electron transport chain. these are synthesized within the mitochondria

Front 13

Where do amino acid modifications occur?

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Back 13

Occur on N AND C terminus and side chains of 15 amino acids

do NOT occur on gly,ala,val,ile, lue - because have unreactive side chains

Front 14

What amino acids are not able to be modified and why?

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Back 14

alanine
gylcine
valine
isoluecine
luecine

because they are aliphatic and have pretty unreactive side groups

Front 15

Is amino acid modification reversible or irreversible?

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Back 15

can be either just depends

Front 16

What roles does amino acid modification serve?

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Back 16

Structural

Functional

Regulatory

Front 17

What are the implications for amino acid modification? Where could it help us to learn something?

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Back 17

Pathology

Pharmocology

Toxicology...

Front 18

What does a perm do to your hair and how?

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Back 18

It reorganizes the disulfide bridges.

Keratin in human hair is 14% cysteine

Disulfide bridges here create the protein structure leading to the type of hair you have.

you oxidize the hair to make new dissulfide bonds.

Front 19

what is phosphorylation frequently used for?

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Back 19

used to control enzyme activity

- usually on Ser, thy or tyr (hydroxyl containing groups)

catalyzed by kinases using ATP

reversible phosphotase action

can increase or decrease activity

Front 20

what are the results of phosphorylating translation initiation factors

eIF2
eIF4E
4E-BP

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Back 20

eIF2 - inhibit

eIF4E - Stiumulate

4E-BP stimulatory (derepression) ie. indirectly stimulates by deactivating something else

Front 21

Functional aspects of post translational modificiations

Back 21

1. Genetic Dieases - MSD

2. Nutrition - Se and SeCys

3. Anticoagulants - vitamin K and warfarin (coumadin)

4. Diabetes mellitus - protein glycation

Front 22

Mutliple Sulfatase Deficiency (MSD)

Back 22

progressive paralysis, skeletal deformities, neurological defects.

Infants develop slowly, lose abilities at 1

Combinees the enzyme deficiency and phenotypic features of several diseases

Front 23

What is the molecular basis of MSD

Back 23

Increased accumulation of mucopolysaccarides (heparan sulfate, dermatan sulfate) and other sulfates (cholesterol sulfate)

Defect in cysteine oxidation common to all sulfatases

Primary defect is in sulfatase-modifying factor-1 gene (SMF-1)

sulfatases cannot be converted to 2-amino-3oxopropionic acid

Front 24

What is selenium?

What are the ramifications of having a diet where you do not get enough selenium?

Back 24

Selenium is an essential micronutrient

Lack of selenium leads to dilated cardiomyopathy, congestive heart failure, striated muscle degeneration, weakenes (AKA Keshan disease)

Front 25

What is Keshan disease caused by and what are its symptoms?

Back 25

caused by lack of selenium

leads to cardiomyopathy, congestive heart failure, flabby heart

Front 26

Why do we need selenium?

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Back 26

because it is an essential part of a small number of proteins (about 25)

most selenoproteins catalyze oxido-reduction reactions

Front 27

What do selenoproteins do? And an example.

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Back 27

they catalyze oxido-reduction reactions

ex. Gluthione peroxidase 5'-delodinases (T4--->T3)

Front 28

What does a Gluthione Peroxidase do?

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Back 28

Destroys reactive damaging H2O2

Reduces organic peroxides (R-OOH to R-OH)

uses Gluthiathione (G-SH) as a reducing agent

Glutathione is oxidized and peroxide is reduced

Front 29

where is glutamate attached to G-SH glutathione?

Back 29

one the gamma carbon

Front 30

What is used to convert dietary idodide to activated iodine [I]ox?

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Back 30

H2O2 thyroperoxidase

Front 31

What is more active T4 or T3?

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Back 31

T3

T4 is thyroxine which has an extra iodine molecule that must be cleaved to form T3

Front 32

What are the steps to processing iodine to be a functional thyroid hormone?

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Back 32

1. Dietary iodide with the help of thyroperoxidase is converted to activated Iodine [I]ox

2. Iodinates tyrosine residue in thyroglobulin

tyr--->mono and di-iodotyrosine (MIT and DIT)

3. MIT + DIT ---> T3 thyroxine chain
DIT + DIT ----> T4

5. T4--->T3 more active catalyzed by 5' deiodinease

Front 33

what is the reaction to convert T4 to T3 catalyzed by?

slide 20

Back 33

5' deiodinase

Front 34

What is goiter caused by?

Back 34

5' deiodinase deficiency

Front 35

When is Selenium incorporated into a protein?

Back 35

Cotranslatinally, ie, at the time of translation

Front 36

How is a selenocysteine incorporated into a protein?

Back 36

considered to be the 21 amino acid.

Uses a modified UGA codon (usually a stop codon.

Later will have a UAA codon and after in the 3' UTR will have SECIS element which helps the cell to recognize that the UGA codon should be the SeCys and not a stop

Front 37

Where and how is selenium attached to protein?

Back 37

Attached to a Ser-tRNA residue by HSePo3^-2 using ATP

becomes SeCys-tRNA

The selenocysteine tRNAs are initially charged with serine by seryl-tRNA ligase, but the resulting Ser-tRNA(Sec) is not used for translation because it is not recognised by the normal translation factor (EF-Tu in bacteria, EF1-alpha in eukaryotes). Rather, the tRNA-bound seryl residue is converted to a selenocysteyl-residue by the pyridoxal phosphate-containing enzyme selenocysteine synthase. Finally, the resulting Sec-tRNA(Sec) is specifically bound to an alternative translational elongation factor (SelB or mSelB) which delivers it in a targeted manner to the ribosomes translating mRNAs for selenoproteins.

Front 38

What is vitamin K essential for?

Back 38

koagulatin

Vitamin K mediates gamma-carboxlation

Front 39

What is selenocystein? selenoprotein?

Back 39

Selenocysteine has a structure similar to cysteine, but with an atom of selenium taking the place of the usual sulfur.
Proteins that contain one or more selenocysteine residues are called selenoproteins.

Front 40

What happens when the SEICS element is deleted in translation of a selenoprotein?

Back 40

the UGA that is normally used in this instance to code for the selenocysteine instead is read as a stop codon and the protein is truncated

Front 41

What reaction does vitamin K mediate?

Back 41

Gamma carboxylation

is a post translational modification where an additional carboxyl is attached to gamma carbon of Glutamate

Front 42

What is Vitamin K / cogulation inhibited by?

slide 22

Back 42

Coumadin
warfarin - used as toxin for rats

Front 43

How can you get a false low AIC?

Back 43

reb blood cells die early.

Can be caused by sickle cell disease, or drugs that cause RBCs to die early

Front 44

Does glycosylation affect the function of RBC?

Back 44

nope but can affect other proteins in the body

Front 45

How does glycosylation of RBC occur?

Back 45

occurs spontaneously, not catalyzed by anything

Front 46

what is AGE?

Back 46

advanced glycosylated endproducts,
caused by gyoslyation of proteins

Front 47

How could you get a false high AIC?

Back 47

RBC live longer than expected. Could be caused by someone who lacks a spleen - this is where RBC go to die