Dynamics of saxitoxin binding to saxiphilin c-lobe reveals conformational change

• Published in: Toxicon (Oxford) 2008-02, Vol.51 (2), p.208-217
• Main Authors: Lewis, Penny, Fritsch, Ingrid, Gawley, Robert E., Henry, Ralph, Kight, Alicia, Lay, Jackson O., Liyanage, Rohana, McLachlin, Jeanne
• Format: Article
• Language: English
• Subjects: Animals; ANS; Bacteriology; Binding Sites; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; Ligand binding; Mass Spectrometry; Medical sciences; Microbiology; Molecular Conformation; Paralytic shellfish toxins; Pathogenicity, virulence, toxins, bacteriocins, pyrogens, host-bacteria relations, miscellaneous strains; Plant poisons toxicology; Poisons - chemistry; PST; Saxiphilin; Saxitoxin; Saxitoxin - chemistry; Shellfish; Surface Plasmon Resonance; Thermodynamics; Toxicology; Δ Cp
• ISSN: 0041-0101; 1879-3150
• DOI: 10.1016/j.toxicon.2007.09.012

Thermodynamic parameters (Δ G, Δ H, Δ S, Δ 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, Δ H°=−11.7±0.8 kcal/mol, and Δ S°=1.17±0.07 cal/mol K. Analysis of Δ 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.