Fig. 4. van der Waals volume contribution to α-BgTx binding explored by mutation at position 152 with (filled circles) or without (open circles) mutant P193I. Each point is the mean ± SE from receptors containing the indicated mutation at position 152. Note that suppression of the putative N-gycosylation signal NWS by mutating S154A in G152N/P193I mutant (sequence NWA) increased apparent affinity binding for α-BgTx (see Table I for values). Data were fitted to the linear regression y = a log[x] + b. Filled circles, R = 0.996 for solid line (a = 56 ± 3 Å³ l/mol) and R = 0.902 for broken line (a = 45 ± 11 Å³ l/mol); open circles, R = 0.758 for chain line (a = 67 ± 33 Å³ l/mol). For the solid line, G152N/S154A/P193I mutant data (sequence NWA) were not included in the linear regression fit.