Protein Targeting

What sequence on a protein helps us target to the endoplasmic reticulum?

The signal sequence is the first part of a ER-targeted protein to be synthesised.

At which peptide terminal is the signal sequence found?

The signal sequence codes for a series of hydrophilic amino acids.

What molecule binds to a protein-ribosome complex and facilitates binding to a receptor on the endoplasmic reticulum?

Through what protein is the new protein guided through after it has been targeted to the endoplasmic reticulum?

Fill in the blanks below to describe protein targeting to the endoplasmic reticulum. 1. The first part of the protein synthesised is the [blank_start]signal sequence[blank_end]. This is a series of [blank_start]hydrophobic[blank_end] amino acids at the [blank_start]N[blank_end]-terminus of the peptide. 2. The [blank_start]signal sequence[blank_end] is recognised by [blank_start]Signal Recognition Particle[blank_end] (SRP). 3. [blank_start]Signal Recognition Particle[blank_end] is recognised by a receptor on the ER membrane. 4. The [blank_start]Signal Recognition Particle[blank_end] is cleaved off, leaving the [blank_start]ribosome[blank_end] bound to the ER membrane. 5. The protein is guided through a t[blank_start]ranslocon[blank_end] protein on the ER membrane as its synthesis continues. 6. The enzyme [blank_start]signal peptidase[blank_end] cleaves the signal sequence off the protein once synthesis is complete.

From which face of the golgi are vesicles budded off for transport?

At which face of the golgi are vesicles received from transport?

SNARE proteins facilitate the targeting of what?

When are v-SNARES incorporated into the membranes of vesicles?

What type of SNARE proteins are present at the target membranes where they will be complementary to a specific v-SNARE?

When does mitochondrial targeting occur?

At which terminus of a mitochondrial-targeted protein will you find the matrix-targeting sequence?

What protein binds to mitochondrial-targeted proteins in the cytosol and matrix to prevent them from folding?

The matrix targeting sequence binds to what?

What import pore is the mitochondrial protein targeted into first?

Cytosolic HSP70 is cleaved from the mitochondrial protein as it enters the first import pore.

What is required to cleave HSP70 chaperone from mitochondrial proteins?

What is the function of matrix processing protease?

Fill in the blanks below to describe how proteins are targeted to the mitochondria. 1. The [blank_start]matrix-targeting sequence[blank_end] is found at the [blank_start]N[blank_end] terminal of the protein. 2. Cytosolic [blank_start]HSP70[blank_end] binds to the protein using energy from [blank_start]ATP[blank_end] to prevent the protein from [blank_start]folding[blank_end]. 3. The [blank_start]matrix-targeting sequence[blank_end] binds to an [blank_start]import receptor[blank_end] on the outer membrane. 4. The [blank_start]import receptor[blank_end] targets the protein through [blank_start]TOM40[blank_end]. Meanwhile, [blank_start]HSP70[blank_end] is cleaved from the protein using [blank_start]ATP[blank_end] hydrolysis. 5. The protein enters the matrix via import pores [blank_start]TIM44[blank_end] and TIM23/[blank_start]17[blank_end]. 6. The protein binds to matrix [blank_start]HSP70[blank_end] to prevent it from [blank_start]folding[blank_end]. 7. [blank_start]Matrix processing protease[blank_end] enzyme cleaves the [blank_start]matrix-targeting sequence[blank_end] from the protein. 8. The protein can now begin [blank_start]folding[blank_end].

When does the targeting of proteins to the nucleus occur?

What property does the Nuclear Localisation Signal have that allows it to target?

What protein does the nuclear localisation sequence bind to?

Ran binds to GTP in the cytosol.

What converts RanGDP to RanGTP in the cytosol?

What happens to RanGTP in the nucleus?

Importin and RanGTP are recycled by their exit from the nucleus after targeting takes place.

What does cytosolic Ran GTPase activated protein do?

What triggers the release of importin from Ran?

Fill in the blanks below to describe the targeting of proteins to the nucleus. 1. The [blank_start]Nuclear Localisation Sequence[blank_end] on the protein binds to [blank_start]importin[blank_end] in the cytosol. 2. Ran binds to [blank_start]GDP[blank_end] in the cytosol. 3. Both of these complexes enter the nucleus via [blank_start]nuclear pores[blank_end]. 4. In the nucleus, Ran [blank_start]Guanine Nucleotide Exchange Factor[blank_end] (RanGEF) converts RanGDP to [blank_start]RanGTP[blank_end]. 5. [blank_start]RanGTP[blank_end] binds to [blank_start]importin[blank_end]. This disrupts [blank_start]importin[blank_end]'s ability to bind to the [blank_start]Nuclear Localisation Sequence[blank_end]. The protein is released. 6. Importin and Ran[blank_start]GTP[blank_end] exit the nucleus via a nuclear pore. 7. Cytosolic Ran [blank_start]GTPase activated protein[blank_end] (Ran GAP) stimulates Ran to hydrolyse [blank_start]GTP[blank_end] to [blank_start]GDP[blank_end]. 8. [blank_start]RanGDP[blank_end] allows the release of [blank_start]importin[blank_end].

What are lysosomal proteins tagged with in the Golgi apparatus?

Mannose-6-phosphate and lysosomal proteins are targeted to transport vesicles in the Golgi via what?

What do transport vesicles from the Golgi containing lysosomal proteins fuse with?

ATP synthase continuously pumps H+ into the endosome containing lysosomal proteins. What does this cause?

M6P receptors used in lysosomal proteins are targeted back to the Golgi.

Fill in the blanks below to describe how proteins are targeted to the lysosomes. 1. Lysosomal proteins are tagged with [blank_start]mannose-6-phosphate[blank_end] in the [blank_start]Golgi apparatus[blank_end]. 2. This complex binds to [blank_start]mannose-6-phosphate[blank_end] receptors and is packaged into [blank_start]vesicles[blank_end]. 3. [blank_start]Vesicles[blank_end] bud off the [blank_start]trans[blank_end] face of the Golgi apparatus and travel to the early [blank_start]endosome[blank_end] with which they fuse. 4. [blank_start]ATP synthase[blank_end] continuously pumps [blank_start]H+[blank_end] ions into the enzyme, reducing the [blank_start]pH[blank_end]. 5. The low [blank_start]pH[blank_end] causes the [blank_start]receptor[blank_end] to be dissociated from the complex as well as [blank_start]dephosphorylation[blank_end] to form a mature hydrolase protein. 6. The receptors are recycled back to the [blank_start]Golgi apparatus[blank_end] via transport [blank_start]vesicles[blank_end].

What disease is caused by a mutation in the enzyme that phosphorylates mannose?

In [blank_start]inclusion-cell[blank_end] disease, the enzyme that phosphorylates [blank_start]mannose[blank_end] is mutated. This means that lysosomal proteins aren't tagged with [blank_start]mannose-6-phosphate[blank_end] so are not targeted to the [blank_start]lysosomes[blank_end]. The [blank_start]lysosomes[blank_end] therefore lose their function and [blank_start]waste[blank_end] accumulates within the cells. This causes developmental defects and often death before the age of 10 due to heart failure/pneumonia.