Structure of Two Tandem-Repeat Galectin Proteins Binding a Model Glycolipid Membrane

Area of Science:

• Biochemistry
• Structural Biology
• Cell Biology

Background:

• Tandem-repeat galectins possess two carbohydrate recognition domains (CRDs) crucial for cell signaling.
• Galectin-4 and Galectin-8 are implicated in intestinal epithelial cells, cell adhesion, immune response, and cancer progression.
• Understanding the membrane-bound structures of these galectins is vital for elucidating their biological functions.

Purpose of the Study:

• To determine the membrane-bound structures of Galectin-4 and Galectin-8.
• To investigate the influence of ligand affinity and linker peptide dynamics on galectin-membrane interactions.
• To provide insights into the conformational dynamics of tandem-repeat galectins.

Main Methods:

• X-ray reflectivity measurements were employed to model the membrane-bound structures.
• Molecular dynamics simulations were utilized for Galectin-4.
• Proteins were studied in lipid monolayers containing ganglioside ligands (GM1 or GM3).

Main Results:

• Galectin-4, with two CRDs and weak GM1 affinity, bound with both CRDs near the membrane, exhibiting dynamic conformations.
• Galectin-8, with one CRD and tight GM3 affinity, showed one CRD oriented towards the membrane and the other away.
• Altering the linker peptide length affected protein binding, suggesting its role in stabilizing CRD contacts.

Conclusions:

• The study elucidates distinct membrane-bound conformations of Galectin-4 and Galectin-8.
• Ligand affinity, linker peptide dynamics, and inter-CRD contacts are critical determinants of galectin-membrane interactions.
• These findings enhance our understanding of tandem-repeat galectin conformational dynamics and their biological implications.