V3-7Sh BCR are selected for β-(1,6)-glucan affinity. (A) SPR curves of binding of pustulan (0, 0.3, 1, and 3 µg/ml) to V3-7Sh sIgM (left) and V3-7Sh sIgM after reversion of somatic mutations (V3-7Sh germline; right). The response curves were fitted to a 1:1 binding model (orange lines). Curves are representative of two independent experiments. (B) Kinetic constants for pustulan binding to V3-7Sh sIgM. k_a in 10⁴ sec⁻¹M⁻¹, k_d in 10⁻⁵ sec⁻¹, K_D in pM. Kinetic constants were calculated with data from at least five different anti-IgM–coated spots. The error value is the deviation in the kinetic constants between different coated spots. For calculations, an estimated average molecular weight of 20 kD was used for pustulan. (C) Association constants (k_a) of pustulan binding to V3-7Sh sIgM with somatic mutations (black bars) and after reversion of somatic mutations to IGHV3-7 germline determined by SPR (white bars). Data are representative of two independent experiments.