Antibody fragments are frequently used as a "crystallization chaperone" to aid structural analysis of complex macromolecules that are otherwise crystallization resistant, but conventional fragment formats have not been designed for this particular application. By fusing an anti-parallel coiled-coil structure derived from the SARAH domain of human Mst1 kinase to the variable region of an antibody, we succeeded in creating a novel chimeric antibody fragment of ∼37 kDa, termed "Fv-clasp," which exhibits excellent crystallization compatibility while maintaining the binding ability of the original IgG molecule. The "clasp" and the engineered disulfide bond at the bottom of the Fv suppressed the internal mobility of the fragment and shielded hydrophobic residues, likely contributing to the high heat stability and the crystallizability of the Fv-clasp. Finally, Fv-clasp antibodies showed superior "chaperoning" activity over conventional Fab fragments, and facilitated the structure determination of an ectodomain fragment of integrin α6β1.

中文翻译：

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Fv-clasp：人为设计的小抗体片段，具有改进的生产兼容性，稳定性和结晶性。

抗体片段经常被用作“结晶伴侣”以帮助复杂的大分子结构分析，否则该大分子具有抗结晶性，但是尚未为该特定应用设计常规片段形式。通过将源自人Mst1激酶的SARAH结构域的反平行卷曲螺旋结构融合到抗体的可变区，我们成功创建了约37 kDa的新型嵌合抗体片段，称为“ Fv-clasp”，该片段具有优异的结晶相容性，同时保持原始IgG分子的结合能力。Fv底部的“ clasp”键和工程化的二硫键抑制了片段的内部迁移率并屏蔽了疏水残基，可能有助于Fv搭扣的高热稳定性和结晶性。最后，Fv-clasp抗体显示出优于常规Fab片段的“陪伴”活性，并促进了整联蛋白α6β1胞外域片段的结构测定。