Question

A protein contains an N-terminal ER signal sequence followed by several negatively charged amino acids, an internal ER stop-transfer sequence, and an internal ER start-transfer sequence (in order from N-terminal to C-terminal). The signal sequence is cleaved by signal peptidase upon lateral release from sec61. How will the protein orient in the ER membrane?

Selected Answer: E. The protein will be soluble and released into the ER lumen

Answers:

A. Lumenal N-terminal, cytosolic C-terminal

B. Lumenal N-terminal, cytosolic protein loop, lumenal C-terminal

C. Cytosolic N-terminal, lumenal protein loop, cytosolic C-terminal

D. Membrane-bound N-terminal, lumenal protein loop, cytosolic protein loop, lumenal C-terminal

E. The protein will be soluble and released into the ER lumen

Answer 1

According to selected answer E,

An ER signal sequence typically is located at the N-terminus of the protein and contains one or more positively charged amino acids followed by a continuous stretch of 6 – 12 hydrophobic residues.

The water soluble proteins are those which are filly tranlocated across ER membrane and are released into the ER lumen.

The orientation of protein in ER will be

A) Lumenal N-terminal, cytosolic C-terminal