Dynamics of saxitoxin binding to saxiphilin c-lobe reveals conformational change
by Lewis, Penny Marie; Fritsch, Ingrid; Gawley, Robert E.; Henry, Ralph L.; Kight, Alicia D.; Lay Jr, Jackson Oliver; Liyanage, Rohana; McLachlin, Jeanne
Thermodynamic parameters (Delta G, Delta H, Delta S, Delta C-p) have been determined to evaluate the dynamics of binding of saxitoxin to the c-lobe of saxiphilin. We have developed an improved method to rapidly express and purify recombinant saxiphilin c-lobe, and fully characterized it by mass spectrometry for the first time. Surface plasmon resonance (SPR) was used to characterize the interaction between saxitoxin and immobilized c-lobe. At 298 K, c-lobe binds saxitoxin with K-D = 1.2 nM, Delta H degrees = -11.7 +/- 0.8 kcal/mol, and Delta S degrees = 1.17 +/- 0.07 cal/mol K. Analysis of Delta C-p of toxin association at several temperatures suggests that hydrophobic forces contribute to the binding event. Additionally, changes in 8-anilino-1-naphthalene sulfonic acid (ANS) fluorescence upon binding to c-lobe in the presence and absence of saxitoxin support a conformational change in c-lobe upon saxitoxin binding. (c) 2007 Elsevier Ltd. All rights reserved.
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