Location of the domains of ICAM-1 by immunolabeling and single-molecule electron microscopy

Area of Science:

• Molecular biology
• Cellular biology
• Biophysics

Background:

• Intercellular Adhesion Molecule 1 (ICAM-1) is a cell surface glycoprotein involved in cell adhesion.
• Soluble ICAM-1, a truncated form, exhibits a rod-like structure with a distinct bend.
• Previous models proposed the bend was between domains D2 and D3, influencing ICAM-1's orientation.

Purpose of the Study:

• To precisely determine the location of the bend in soluble ICAM-1.
• To clarify the structural organization of ICAM-1 and its functional implications.

Main Methods:

• Single-molecule electron microscopy was employed to visualize soluble ICAM-1.
• Monoclonal antibodies specific to ICAM-1 domains D1 and D4 were used for labeling.
• Structural analysis focused on identifying the precise location of the molecular bend.

Main Results:

• The study revealed the bend in soluble ICAM-1 is located between domains D3 and D4.
• This finding contradicts previous hypotheses placing the bend between D2 and D3.
• The short arm of ICAM-1, containing D1 and D2, is closer to the plasma membrane.

Conclusions:

• The long arm of ICAM-1, comprising domains D3-D5, contains all known ligand-binding sites.
• This structural arrangement positions the ligand-binding regions towards the target cell surface.
• Understanding ICAM-1's precise structure is crucial for elucidating its role in cell adhesion and immune responses.