An acidic loop within the human soluble CD23 protein may direct the interaction between sCD23 and the αXβ2 integrin

Abstract

CD23 is involved in a myriad of immune reactions. It is not only a receptor for IgE, but also functions in the regulation of IgE synthesis, isotype switching in B cells, and induction of the inflammatory response. These effector functions of CD23 arise through its interaction with another leukocyte-specific cell surface receptor – the β2 integrin subfamily. It has been shown that CD23 is also capable of interacting with the β3 and β5 integrin β-subunit of integrins via a basic RKC motif in a metal cation-independent fashion. In this study the interaction was probed for whether or not the RKC motif governs the interaction between CD23 and the αXβ2 integrin as well. This was done by performing bioinformatic docking predictions between CD23 and αXβ2 integrin αI domain and SPR spectroscopy analysis of the interaction. This revealed that in the absence of cations, the RKC motif is involved in interaction with the integrin αI domain. However, in the presence of divalent metal cations the interaction showed the involvement of a novel acidic motif within the CD23 protein. This same pattern of interaction was seen in docking predictions between CD23 and the β3I-like domain. This study thus presents an alternative site as a possible contributor to the CD23-integrin interaction exhibiting cation-dependence.