Analysis of the interaction of tarantula toxin Jingzhaotoxin-III (ß-TRTX-Cj1α) with the voltage sensor of Kv2.1 uncovers the molecular basis for cross-activities on Kv2.1 and Nav1.5 channels.

Animal venoms contain a fascinating array of divergent peptide toxins that have cross-activities on different types of voltage-gated ion channels. However, the underlying mechanism remains poorly understood. Jingzhaotoxin-III (JZTX-III), a 36-residue peptide from the tarantula Chilobrachys jingzhao, is specific for Nav1.5 and Kv2.1 channels over the majority of other ion channel subtypes. JZTX-III traps the Nav1.5 DII voltage sensor at closed state by binding to the DIIS3-S4 linker. In this study, electrophysiological experiments showed that JZTX-III had no effect on five voltage-gated potassium channel subtypes (Kv1.4, Kv3.1, and Kv4.1-4.3), whereas it significantly inhibited Kv2.1 with an IC50 of 0.71 ± 0.01 µM. Mutagenesis and modeling data suggested that JZTX-III docks at the Kv2.1 voltage-sensor paddle. Alanine replacement of Phe274, Lys280, Ser281, Leu283, Gln284, and Val288 could decrease JZTX-III affinity by 7-, 9-, 34-, 12-, 9-, and 7-fold, respectively. Among them, S281 is the most crucial determinant, and the substitution with Thr only slightly reduced toxin sensitivity. In contrast, a single conversion of Ser281 to Ala, Phe, Ile, Val, or Glu increased the IC50 value by >34-fold. Alanine-scanning mutagenesis experiments indicated that the functional surface of JZTX-III bound to the Kv2.1 channel is composed of four hydrophobic residues (Trp8, Trp28, Trp30, and Val33) and three charged residues (Arg13, Lys15, and Glu34). The bioactive surfaces of JZTX-III interacting with Kv2.1 and Nav1.5 are only partially overlapping. These results strongly supported the hypothesis that animal toxins might use partially overlapping bioactive surfaces to target the voltage-sensor paddles of two different types of ion channels. Increasing our understanding of the molecular mechanisms of toxins interacting with voltage-gated sodium and potassium channels may provide new molecular insights into the design of more potent ion channel inhibitors.

Randomised clinical trial evaluating best-corrected visual acuity and central macular thickness after 532-nm subthreshold laser grid photocoagulation treatment in diabetic macular oedema.

PURPOSE: To compare best-corrected visual acuity (BCVA) and central macular thickness (CMT) after 532-nm subthreshold laser grid photocoagulation and threshold laser grid photocoagulation for the treatment of diabetic macular oedema (DME). PATIENTS AND METHODS: Twenty-three patients (46 eyes) with binocular DME were enroled in this study. The two eyes of each patient were divided into a subthreshold photocoagulation group and a threshold photocoagulation group. The eyes of the subthreshold group underwent 532-nm patter scan laser system (PASCAL) 50% end point subthreshold laser grid photocoagulation therapy, whereas the threshold photocoagulation group underwent short-pulse grid photocoagulation with a 532-nm PASCAL system. BCVA and CMT were assessed in all patients before treatment, 7 days after treatment, and 1, 3, and 6 months after treatment. RESULTS: After grid photocoagulation, the mean BCVA improved in both the subthreshold group, and the threshold group, and the two groups did not differ statistically significantly from each other. Similarly, the macular oedema diminished in both groups after treatment, and the two groups did not differ statistically significantly from each other with regard to CMT. CONCLUSION: Both 532-nm subthreshold laser grid photocoagulation and threshold laser grid photocoagulation can improve the visual acuity and reduce CMT in DME patients.