EVIDENCE FOR AN ACTIN-BINDING HELIX IN GELSOLIN SEGMENT-2 - HAVE HOMOLOGOUS SEQUENCES IN SEGMENT-1 AND SEGMENT-2 OF GELSOLIN EVOLVED TO DIVERGENT ACTIN-BINDING FUNCTIONS

Gelsolin is built up of six homologous segments that perform different functions on actin, Segments 1 and 2, which are suggested to be highl y similar in their overall folds, bind monomeric and filamentous actin respectively, A long alpha-helix in segment 1 forms the major contact site of this segment with actin, We show that sequence 197-226 of seg ment 2, equivalent to the region around the actin binding helix in seg ment 1, contains F-actin binding activity, Consequently, positionally similar parts of segment 1 and 2 are implicated in the actin contact a nd solvent exposed residues in these parts must have evolved different ially to meet their different actin binding properties.