PI(4)-dependent recruitment of clathrin adaptors to the trans-Golgi Network
The Trans Golgi Network (TGN) is the cell’s central sorting station, and the
complex trafficking patterns are organized by many types of trafficking adaptors. These
include the heterotetrameric adaptor protein complexes (APs) and the monomeric Golgilocalized,
?-ear containing, Arf-binding proteins (GGAs). The fundamental question of how
these adaptors are recruited to TGN membrane remains unclear.
Previous studies have shown that adaptor recruitment to the TGN is absolutely
dependent on the small GTPase ADP ribosylation factor 1 (Arf1), but paradoxically, Arf1
has a broader intracellular distribution than these adaptors. We found that the Golgi is
particularly enriched in phosphatidylinositol 4 phosphate [PI(4)P] and that the clathrin
adaptor AP-1 binds PI(4)P directly, suggesting that PI(4)P binding may specify the TGNspecific
recruitment in conjunction with Arf1.
My studies showed that another monomeric clathrin adaptor GGA also binds
PI(4)P and Arf1 independently. The C-terminal “triple helix bundle” of the GGA GAT
domain is a polyfunctional module that interacts with multiple partners including PI(4)P
and ubiquitin, and ubiquitin may provide a recognition signal for GGAs to control protein
sorting. We found that PI(4)P increases wild type GAT binding to ubiquitin-conjugated
agarose beads, but has no effect on a mutant GAT that does not bind PI(4)P. Therefore,
PI(4)P may be an allosteric regulator of GGAs which enhances ubiquitin binding to GGAs.
Based on these results, we conclude: (1) PI(4)P defines the TGN organelle identity
by recruiting TGN-targeted adaptors; (2) TGN-enriched adaptors are recruited to the Golgi
by binding to both PI(4)P and Arf1, and neither alone is sufficient; (3) PI(4)P acts as a
scaffold, and may also be an allosteric regulator for GGAs that modulates GGA function
with other ligands.
We propose that the integration of combinatorial inputs from PI(4)P, Arf1 and
ubiquitin may coordinately specify clathrin adaptor TGN recruitment through multiple
School:The University of Texas Southwestern Medical Center at Dallas
School Location:USA - Texas
Source Type:Master's Thesis
Keywords:dissertations academic trans golgi network clathrin transcription factor ap 1 vesicular transport proteins adp ribosylation phosphatidylinositol phosphates ubiquitin adaptor texas
Date of Publication:01/01/2005