KINETIC-ANALYSIS OF THE INTERACTIONS OF RECOMBINANT HUMAN VPREB AND IG-V DOMAINS

The surrogate light chain, composed of VpreB and lambda 5/14.1 protein s, is selectively expressed on B cell precursors, and is important for B cell development. The surrogate light chain associates with cell su rface mu-chains on preB cells, but little is known about the ligand sp ecificity and affinity of VpreB binding, To analyze its interactions w ith Igs, we made recombinant human VpreB protein and measured its affi nity for H and L chain V domains using surface plasmon resonance. The recombinant VpreB protein existed as a homodimer in solution. VpreB ch ains associated with each other with an apparent K-d = 5 x 10(-7) M, a nd hound to a human VH domain, a mouse VH domain, and a human VL domai n with a similar affinity. VpreB protein also bound to human Fab fragm ents of IgG with an apparent K-d = 6 X 10(-7) M, but showed a very low affinity for human Fc fragments of IgG. VpreB-Fab complex formation w as reproduced by the formation of a trimolecular VpreB-VH-VL complex, Thus, VpreB proteins can associate with each other and also form compl exes with Ig at sites different from those involved in VH-VL interacti on, By flow cytometry, biotinylated VpreB protein bound to surface Ig- positive B cells but not T cells, Receptors that contain VpreB could b e cross-linked by either Ig or by self-association.