DEFINITION OF THE EGTA-INDEPENDENT INTERFACE INVOLVED IN THE SERUM GELSOLIN ACTIN COMPLEX

The gelsolin-actin complex in the presence of Ca2+ revealed at least t hree interacting sites on the gelsolin molecule located in the S1, S2- 3, and S4-6 domains. In the presence of EGTA, the N-terminal domain of gelsolin is known to be involved. However. the corresponding site on the surface of actin is poorly defined. The present result locates the Ca2+-independent plasma gelsolin-binding site on the actin surface. N atural and synthetic actin peptides were tested for their possible int eraction with gelsolin and monitored by fluorescence anisotropy measur ements and e.l.i.s.a. The interface was thus located within the 360-37 2 actin sequence near the C-terminal extremity. In addition, we used a chymotryptic digest of gelsolin and determined that its N-terminal do main (S1) was implicated in this interface. We conclude that the inter action of the 41-126 region of plasma gelsolin is the counterpart of t he 360-372 sequence in subdomain 1 of actin.