Question

Please explain three golgi independent pathways of cholestorol and phospholipid transportation between organelles in details

Answer 1

Golgi independent pathway or Unconventional protein secretion (UPS) is divided into four types, i.e. Type I, II and III UPS of leaderless proteins, and Type IV UPS of Golgi-bypassing transmembrane proteins (Rabouille et al.)

1. (Type I) direct secretion or pore-mediated translocation across the plasma membrane.

2. (Type II) ATP-binding cassette (ABC) transporter-based secretion (McGrath and Varshavsky, 1989) and,

3. (Type III) membrane-bound organelle (autophagosome/endosome)-based secretion.

4. Type IV UPS of leader-sequence-containing transmembrane proteins, which are synthesized in the ER and reach the plasma membrane by bypassing the Golgi .