STRUCTURE OF GELSOLIN SEGMENT-1-ACTIN COMPLEX AND THE MECHANISM OF FILAMENT SEVERING

The structure of the segment 1 domain of gelsolin, a protein that frag ments actin filaments in cells, is reported in complex with actin. Seg ment 1 binds monomer using an apolar patch rimmed by hydrogen bonds in a cleft between actin domains. On the actin filament model it binds t angentially, disrupting only those contacts between adjacent subunits in one helical strand. The segment 1 fold is general for all segments of the gelsolin family because the conserved residues form the core of the structure. It also provides a basis for understanding the origin of an amyloidosis caused by a gelsolin variant.