Question

For retrieval of ER proteins from the Golgi, the signals involved are?

1) KDEL
2) KKXX
3) KXKXX
4) KXKX

Answer 1

ER proteins are retrieved from the Golgi apparatus using specific signals, the most common of which is KDEL for soluble proteins and KKXX or KXKXX for membrane proteins. These signals are recognized by receptors in the Golgi, which package the proteins into vesicles for return to the ER.

Step-by-step explanation:

For the retrieval of endoplasmic reticulum (ER) proteins from the Golgi apparatus, the signal involved is KDEL (Lys-Asp-Glu-Leu) at the C-terminus of the protein. Other sequences, such as KKXX or KXKXX, are also involved in the retrieval of membrane proteins to the ER.

In the process of protein synthesis and sorting, proteins made in the rough endoplasmic reticulum (RER) are transported in vesicles that bud off and eventually fuse with the Golgi apparatus. These proteins undergo post-translational modifications as they move through the cis, medial, and trans regions of the Golgi stacks. Certain proteins require retrieval back to the ER and feature specific retrieval signals for this purpose. The KDEL sequence on soluble proteins and KKXX or KXKXX sequences on membrane proteins are recognized by retrieval receptors in the Golgi, leading to their packaging into vesicles that will transport them back to the ER. This system ensures that ER resident proteins are kept within the ER, maintaining proper cell function and compartmentalization.