Mutations in the basic domain and the loop-helix II junction of TWIST abolish DNA binding in Saethre-Chotzen syndrome

Saethre-Chotzen syndrome is an autosomal dominant skull disorder resulting from premature fusion of coronal sutures (craniosynostosis), It is caused b y mutations in the TWIST gene encoding a basic Helix-Loop-Helix transcripti on factor. Here me report on the identification of a novel mutation affecti ng a highly conserved residue of the basic domain. Unlike nonsense and miss ense mutations lying within helices, this mutation does not affect protein stability or heterodimerisation of TWIST with its partner E12, However, it does abolish TWIST binding capacity to a target E-box as efficiently as two missense mutations in the loop-helix II junction. By contrast, elongation of the loop through a 7 amino acid insertion appears not to hamper binding to the DNA target. We conclude that loss of TWIST protein function in Saeth re-Chotzen patients can occur at three different levels, namely protein sta bility, dimerisation, and DNA binding and that the loop-helix II junction i s essential for effective protein-DNA interaction, (C) 2001 Federation of E uropean Biochemical Societies. Published by Elsevier Science B. V. All righ ts reserved.