Structural basis for recognition of acidic-cluster dileucine sequence by GGA1

Abstract

GGAs (Golgi-localizing, gamma-adaptin ear homology domain, ARF-interacting proteins) are critical for the transport of soluble proteins from the trans-Golgi network (TGN) to endosomes/lysosomes by means of interactions with TGN-sorting receptors, ADP-ribosylation factor (ARF), and clathrin. The amino-terminal VHS domains of GGAs form complexes with the cytoplasmic domains of sorting receptors by recognizing acidic-cluster dileucine (ACLL) sequences. Here we report the X-ray structure of the GGA1 VHS domain alone, and in complex with the carboxy-terminal peptide of cation-independent mannose 6-phosphate receptor containing an ACLL sequence. The VHS domain forms a super helix with eight alpha-helices, similar to the VHS domains of TOM1 and Hrs. Unidirectional movements of helices alpha6 and alpha8, and some of their side chains, create a set of electrostatic and hydrophobic interactions for correct recognition of the ACLL peptide. This recognition mechanism provides the basis for regulation of protein transport from the TGN to endosomes/lysosomes, which is shared by sortilin and low-density lipoprotein receptor-related protein.

Autoinhibition of the ligand-binding site of GGA1/3 VHS domains by an internal acidic cluster-dileucine motif

“…Previous reports have established that the VHS domains of all three GGAs bind to AC-LL motifs (8)(9)(10)(11)(12)(13). However, the studies with GGA1 and GGA3 used truncated forms of the proteins rather than full-length molecules.…”

“…The GAT domain binds to the GTP-bound form of the ADP-ribosylation factor (ARF) family of proteins that serve to recruit the GGAs from the cytosol to the Golgi complex (4,6,7). The VHS domain then interacts specifically with the acidic cluster (AC)-dileucine motif found in the cytoplasmic tails of sorting receptors such as sortilin, the cation-independent mannose 6-phosphate receptor (CI-MPR), and the cation-dependent mannose 6-phosphate receptor (CD-MPR), as well as the lowdensity lipoprotein receptor-related protein 3 (LRP3) (8)(9)(10)(11)(12)(13). Although the precise function of the GAE domain is not clear, it has been shown to interact with ␥-synergin, rabaptin-5, and at least in the case of GGA1 with clathrin (3,5,6,9).…”

A novel conserved targeting motif found in ABCA transporters mediates trafficking to early post-Golgi compartments

“…uses the "Golgi-localized ␥ -ear-containing ARF binding proteins" (GGA), ubiquitous cytosolic proteins that are essential for the accurate traffi cking of MPRs from the TGN to endosomes ( 49 ). The GGAs recognize an acid clusterdileucine signal in the cytosolic tail of MPRs ( 50 ). Thus, although the binding cytosolic partner(s) for ABCA transporters have yet to be determined, it is likely that cytosolic adaptors for ABCA transporters exist not only to mediate delivery to their fi nal destinations but also to allow their initial transient segregation (via xLxxKN motif) within common vesicles prior to their subsequent traffi cking steps.…”

Cell Surface Expression of the Melanocortin-4 Receptor Is Dependent on a C-terminal Di-isoleucine Sequence at Codons 316/317

“…Acidic dihydrophobic motifs, in particular di-leucine pairs preceded by a cluster of acidic amino acids, have been shown to be sorting receptor binding sites for the GGA (Golgi-localizing, ␥-adaptin ear homology domain, ARF-interacting) proteins required for the transport of protein cargo from the trans-Golgi network to endosomes (24,25). The C-terminal dihydrophobic motif that appears in GPCRs is preceded, in many GPCRs, by a conserved acidic amino acid (18).…”