Structure of a new neurotoxin from the scorpion Buthus martensii Karsch at 1.76 Å

Abstract

A new neurotoxin BmK M2, toxic to both mammals and insects, with the strongest toxicity in the BmK toxin series, has been purified from the Chinese scorpion Buthus martensii Karsch and crystallized with MPD at pH 7.5. The crystals are orthorhombic, belonging to space group P2(1)2(1)2(1), with unit-cell parameters a = 36.64, b = 36.95, c = 37.23 A. The structure was solved by molecular replacement and refined to R = 0.186 for all reflections to a resolution of 1.76 A. The whole sequence (64 residues) of BmK M2 was determined by crystallographic analysis based on high-resolution data and the homologous model of BmK M8. The refined BmK M2 structure shows a non-proline cis peptide bond between Pro9 and His10 which enables the C-terminal segment to adopt a conformation different to that of the weak toxin BmK M8. Recently, a mutation analysis had suggested that both the tenth residue and the C-terminus play key roles in receptor binding. Therefore, these features may be related to the binding selectivity of the group III alpha-like toxins. The charge changes of residues 8, 10, 18, 28, 55 and 59 from neutral or negative to positive or neutral, which leads to a positive electrostatic potential surface, may be responsible for the high toxicity of BmK M2.

Molecular Basis of the High Insecticidal Potency of Scorpion α-Toxins

“…Whereas a non-proline cis peptide bond was observed between residues 9 and 10 of all scorpion ␣-toxins active on insects (Lqh3, PDB ID 1FH3; BmK-M1, PDB ID 1SN1; BmK-M4, PDB ID 1SN4; Lqh␣IT, unpublished), the same bond assumes a trans conformation in the classic antimammalian toxins Aah2 and BmK-M8 (43,44). The occurrence of a non-proline cis peptide bond in proteins is quite rare due to a steric strain as a result of repulsion of the neighboring C ␣ atoms and is compensated by local stabilizing interactions.…”

“…The Core-domain in Lqh␣IT is colored in blue. Lqh␣IT (37) and Lqh3 (56) are from L. quinquestriatus hebraeus; BmK-M1, BmK-M2, BmK-M4, and BmK-M8 (39,44) are from B. martensii Karsch; and Aah2 is from A. australis hector (38).…”

Characterization of scorpion α‐like toxin group using two new toxins from the scorpion Leiurus quinquestriatus hebraeus

“…The existence of the α‐like toxins as a distinct group is further strengthened by structural analysis. All scorpion toxins affecting Na current inactivation are a homologous class of polypeptides with highly similar 3D structure ([17, 40–43]; Fig. 7A).…”

Crystal structure of a highly acidic neurotoxin from scorpion Buthus tamulus at 2.2 Ǻ resolution reveals novel structural features

“…There is another face with positively charged residues that are protruding in the third direction. Despite an overall similar scaffolding, the present structure of B. tamulus neurotoxin (BTN) presents novel features that are highly suggestive of its potential binding properties to receptors and these have not yet been observed in the previous structures reported so far (Cook et al, 2002;He et al, 1999He et al, , 2000Housset et al, 1994;Huang et al, 2003;Li et al, 1996;Oren et al, 1998;Pinheiro et al, 2003;Polikarpov et al, 1999;Szyk et al, 2004;Zhao et al, 1992).…”

“…Therefore, the elucidation of their three-dimensional structures and correlationship with their binding properties will provide valuable information for the design of selective drugs and insecticides. Although crystal structures of several scorpion toxins have been determined (Cook et al, 2002;He et al, 1999He et al, , 2000Huang et al, 2003;Housset et al, 1994;Li et al, 1996;Oren et al, 1998;Pinheiro et al, 2003;Polikarpov et al, 1999;Szyk et al, 2004;Zhao et al, 1992), it has not yet been possible to identify unique features that could be linked to their specific pharmacological properties. Therefore, new structures with novel features may be needed to establish the precise structure-function relationships.…”