Complex of ADP-ribosylation factor 1 and ADP-ribosylation factor binding protein GGA1
Mus musculus (house mouse)
Animal cells contain about 10 billion protein molecules of perhaps 10,000-20,000 kinds. All proteins are synthesized in the cytosol and transferred to organelles such as nucleus, endoplasmic reticulums, the Golgi apparatuses, lysosomes or mitochondria, depending on their specific tasks. Except for the proteins that function in the cytosol, almost all proteins are transferred to endoplasmic reticulums, and then those are moved to Golgi apparatuses. After being processed in the Golgi apparatuses, the proteins take one of three routes: (1) going out from that cell immediately, (2) being stocked in cytosol as secretory vesicle for later usage, (3) being destroyed on pathway through endosomes and lysosomes. Transfer systems for cargo proteins are well established in the cell. At the downstream of an endoplasmic reticulum, cargo proteins are transferred via the vesicular transport system by special proteins which make cages. Many proteins are involved in packaging of cargo proteins, including: 1) cargo protein receptors, 2) proteins which make the cage (e.g. clathrin), 3) adapter proteins connecting cargo receptors and clathrins, 4) proteins which cut the vesicle from a membrane, 5) coat-recruitment GTPase proteins which bring adapter proteins close to a membrane (e.g. ADP-ribosylation factor, ARF). By the coordinated functioning of these proteins, cargo proteins are transferred to the appropriate destinations.
The crystal structure shown here is a complex of membrane bound form (GTP form) of ARF with a domain of an adapter protein called “Golgi-localizing, gamma-adaptin ear homology domain, ARF-binding proteins (GGA)”. In the cell, ARF and GGA are working at the exit site of Golgi apparatuses for transferring cargo proteins to endosomes and lysosomes for destruction. The part of GGA interacting with ARF, called “GGA and Tom1 (GAT)”, is composed of a helix-loop-helix in complex structure, and the interacting part of ARF is inter-switch region formed by a beta-sheet with two antiparallel strands. These bind with each other mainly by hydrophobic manner but there are additional hydrogen bonds. This complex structure revealed the atomic level mechanisms how adapter proteins are recruited to membrane, as a part of vesicular transport systems.
Protein Data Bank (PDB)
Shiba, T. Kawasaki, M. Takatsu, H. Nogi, T. Matsugaki, N. Igarashi, N. Suzuki, M. Kato, R. Nakayama, K. Wakatsuki, S.; "Molecular mechanism of membrane recruitment of GGA by ARF in lysosomal protein transport"; NAT.STRUCT.BIOL.; (2003) 10:386-393 PubMed:12679809.
author: Sachiyo Nomura