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

Area of Science:

• Molecular Biology
• Cell Biology
• Structural Biology

Background:

• Golgi-localizing, gamma-adaptin ear homology domain, ARF-interacting proteins (GGAs) are essential for protein transport from the trans-Golgi network (TGN) to endosomes/lysosomes.
• GGAs interact with sorting receptors, ADP-ribosylation factor (ARF), and clathrin to facilitate this process.
• The VHS domains of GGAs recognize acidic-cluster dileucine (ACLL) motifs on sorting receptors.

Purpose of the Study:

• To elucidate the structural basis of ACLL sequence recognition by the GGA1 VHS domain.
• To understand the molecular mechanisms underlying TGN-to-endosome protein sorting.

Main Methods:

• X-ray crystallography was employed to determine the structure of the GGA1 VHS domain.
• Complex structures were solved for the GGA1 VHS domain bound to a peptide containing the ACLL motif from the cation-independent mannose 6-phosphate receptor.

Main Results:

• The GGA1 VHS domain adopts a superhelical structure composed of eight alpha-helices.
• Specific movements in helices alpha6 and alpha8, along with their side chains, mediate electrostatic and hydrophobic interactions for ACLL peptide binding.
• This mechanism is conserved in other VHS domains, such as those in TOM1 and Hrs.

Conclusions:

• The identified structural mechanism explains how GGA VHS domains recognize ACLL sequences for cargo selection.
• This provides insights into the regulation of protein transport from the TGN to endosomes/lysosomes.
• The recognition mechanism is shared with other proteins like sortilin and low-density lipoprotein receptor-related protein.