General - Protein tag sequences

Question 1

YxxO

Answer 1

Tyrosine based sequence, often on cytosolic domain of receptors. Tag for AP-2 recognition

Question 2

D/E xxx L L/I

Answer 2

dileucine based sequence, often found on lysosomal integral membrane proteins, a tag for AP-2 recognition

Question 3

Lysine 48

Answer 3

Ubiquitin linking site

Question 4

NPVY

Answer 4

Sequence required to internalize the LDLR receptor. The tyrosine is essential, the vlaine is not. Most internalized cell surface receptors have a similar sort of internalization sequence. (I guess it’s probably not through AP-2)

Question 5

Does clathrin interact with the NPxY signal?

Answer 5

No, there has to be something in between!!

Question 6

D/E xx L L/I

Answer 6

NOTE: NOT THE SAME AS THE ONE RECOGNIZED BY AP-2 - that’s D/E xxx L L/I

This is recognized by GGA - golgi, localized gamma ear containing Arf-binding, used for endosomal sorting. Binds to clathrin via hinge region.

How lysosomal enzymes get sorted into the TGN –> Basically Mannose 6 phosphate binds to M6PR on target lysosomal enzymes in the TGN. Then GGAs recognize the DxxLL signal. GGAs recruit clathrin to form clathrin coated vesicles which get targetd to late endosomes. MPR falls off of M6P.

Question 7

PX domain

Answer 7

Binds PtdIns(3)P 
Sorting nexins have these

So… Rab5 –> Ptdins3 –> ESCRTS and sorting nexins

Father had rabies so he was escorted inside to his nephew…

Question 8

BAR domain

Answer 8

Binds curved membrains. Most sorting nexins carry these.

Question 9

Asn-X-Ser/Thr

Answer 9

N-linked sugars are added co-translationally to Asn residues in this sequence in order to help with monitoring whether the protein is properly folded

Question 10

CAAX Motif

Answer 10

Contained on the C-terminal tail of Lamin proteins. Allows them to insert into the membrane directly.

Question 11

FG

Answer 11

Phenylalanine-glycine repeat motif, found on Nsp / Nuclear pore complex. If you mutate it you get hydrogel that falls apart.

Question 12

Pro-Pro-Lys-Lys-Lys-Arg-Lys-Val

PKKKRKV

Answer 12

Localization signal of SV40 to nucleus

Question 13

KR(X10)KKKK

Answer 13

Consensus bipartate nuclear localization sequence.