Relationship between binding characteristic of a non-natural peptide, Lei-Dab7, and distribution of SK subunits in the rat central nervous system


  • Aidi-Knani S.
  • Pezard L.
  • Mpari B.
  • Ben Hamida J.
  • Sabatier J.-M.
  • Mourre C.
  • Regaya I.

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Small-conductance calcium-activated potassium channels (SK), among which, three subunits were identified (SK1-3), were initially studied using apamin and to know the structure-function relationship studies of this toxin. Apamin, a neurotoxin blocker, extracted from bee venom, includes 18 amino acid residues reticulated by two disulfure bridges and reported to be the reference ligand of SK2 and SK3 channels because of its high affinity for both of them. More recently, using the radiolabeled apamin competition assays, other blockers were found in different scorpion venoms, such as Leirotoxin1 (LTX1) and P05. These toxins of 31 residues of amino acids, reticulated by three disulfure bridges, have 87 to 90 % of sequence homology. Sequence alignment has shown that LTX1 and PO5 contain a motif (RXCQ) reported to be important for binding to SK channels. Apamin contains a RRCQ sequence, having a spatial arrangement (α helix) similar to that of the RXCQ motif in LTX1 and P05. LTX1 and PO5, potently blocked human SK2 and SK3 but not SK1. By replacing Met(7) in the RXCQ motif of LTX1 with the shorter, unnatural, positively charged diaminobutanoic acid (Dab), we generated Lei-Dab7, a selective SK2 inhibitor (Kd = 3.8 nM). This study evaluates the relationships between selectivity and affinity of apamin and Lei-Dab7. Competitive binding of radio-iodinated apamin to rat brain regions, in presence of native apamin and Lei-Dab7, has shown dissociation constants significantly different by a factor of a thousand, signifying that ligand affinity is as important as selectivity for binding a specific receptor. To evaluate the differences of the binding characteristics in rat brain structures, we used a message-passing clustering techniques. Five groups of brain structures were identified reflecting a singular profile of affinity and selectivity of Lei-Dab7 in comparison with apamin. A multiple correspondences analysis allowed us to analyze the correspondences between Lei-Dab7 binding and expression of SK subunits in these brain structures groups. The comparison between the selectivity of Lei-Dab7 and the composition in SK subunits in brain regions suggest functional heteromeric SK channels. Our analysis contributes to a better understanding of the molecular combination of SK channel in the native tissue involved in specific information processes.

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