Structural basis for acidic-cluster-dileucine sorting-signal recognition by VHS domains

Area of Science:

• Cell biology
• Molecular biology
• Structural biology

Background:

• Transmembrane protein sorting to the endosomal-lysosomal system relies on specific signals.
• Acidic-cluster-dileucine motifs in receptors like M6PRs are recognized by GGA proteins.
• The VHS domain of GGA proteins mediates the specific recognition of these sorting signals.

Purpose of the Study:

• To elucidate the structural basis of the interaction between GGA VHS domains and acidic-cluster-dileucine sorting signals.
• To understand the molecular mechanisms underlying the specificity of this protein-signal recognition.

Main Methods:

• X-ray crystallography was used to determine the structures of the human GGA3 VHS domain.
• Complex structures were obtained with peptide signals derived from cation-independent and cation-dependent mannose-6-phosphate receptors.

Main Results:

• The structures reveal that acidic-cluster-dileucine signals bind in an extended conformation to helices 6 and 8 of the VHS domain.
• A critical recognition element is an Asp residue positioned two residues upstream of a dileucine motif (Asp-X-X-Leu-Leu).
• Specific interactions involve the Asp side chain binding to an electropositive subsite, and the dileucine residues interacting with two hydrophobic pockets, ensuring high specificity.

Conclusions:

• The determined structures provide atomic-level insight into the recognition of sorting signals by GGA VHS domains.
• The precise spatial arrangement of binding subsites within the VHS domain dictates the high specificity for acidic-cluster-dileucine signals.
• This understanding is crucial for comprehending protein trafficking pathways within the cell.