An acidic loop within the human soluble CD23 protein may direct the interaction between sCD23 and the α_Xβ₂ integrin

Area of Science:

• Immunology
• Cell Biology
• Biochemistry

Background:

• CD23 is a multifunctional receptor involved in IgE regulation, B cell isotype switching, and inflammatory responses.
• CD23 interacts with leukocyte integrins, including the β2 subfamily, mediating its effector functions.
• Previous studies indicated CD23 interacts with β3 and β5 integrin β-subunits via a cation-independent RKC motif.

Purpose of the Study:

• To investigate if the RKC motif governs the interaction between CD23 and the αXβ2 integrin.
• To identify the interaction mechanism between CD23 and αXβ2 integrin, particularly its cation-dependence.

Main Methods:

• Bioinformatic docking predictions between CD23 and the αXβ2 integrin αI domain.
• Surface Plasmon Resonance (SPR) spectroscopy analysis to study the CD23-integrin interaction.
• Analysis of CD23 interaction with β3I-like domain.

Main Results:

• In the absence of cations, the RKC motif of CD23 is involved in the interaction with the αXβ2 integrin αI domain.
• In the presence of divalent metal cations, a novel acidic motif within CD23 mediates the interaction with αXβ2 integrin.
• Similar cation-dependent interaction patterns were observed between CD23 and the β3I-like domain.

Conclusions:

• The CD23-integrin interaction exhibits cation-dependence, involving distinct motifs.
• A novel acidic motif in CD23 contributes to cation-dependent interactions with leukocyte integrins.
• These findings present an alternative binding site contributing to CD23-integrin interactions.