Gelsolin was cleaved by chymotrypsin or thermolysin into an N-terminal Mr 45 000 fragment (45N) and a C-terminal Mr 38 000 fragment (38C). The N-terminal half was further cleaved into two fragments with Mr 17000 (17N) and Mr 28000 (28N). These fragments were complexed with actin and cross-linked with 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide (EDC) to introduce covalent bonds into their contact sites. The location of these bonds was mapped along the actin sequence by end-label fingerprinting with highly sensitive probes for the N- and C-termini of actin. The mapping studies revealed that two gelsolin N-terminal fragments (17N and 28N) were cross-linked with the actin N-terminal segment, while the gelsolin C-terminal fragment (38C) was cross-linked with the actin C-terminal segment. The result indicates that the actin N- and C-terminal segments are in the binding site of gelsolin.
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