Interchain and intrachain crosslinking of actin thiols by a bifunctional thiol reagent.

From 1,9-nonylenedithiol and Ellman's Reagent the bifunctional asymmetric disulfide n-nonylene-1,9-bis-[5-dithio-(2-nitrobenzoic acid)] (NBDN) was prepared. By monovalent reaction with cysteine-374 the crosslinker could be introduced into monomeric actin, with release of one equivalent of yellow 2-nitro-5-thiobenzoate (NTB). From the monovalent actin derivative we prepared a crosslinked actin dimer (Cys-374-Cys-374') as well as a monomer with a crosslink between Cys-374 and Cys-10. Neither crosslinked actin species was able to polymerize the crosslinked monomer even in the presence of phalloidin. The crosslinked monomer polymerized on the addition of dithiothreitol, thus providing the first unpolymerizable actin species whose polymerizability can be restored under mild conditions. We suggest the use of NBDN as a thiol-specific crosslinker that reacts under spectrophotometric control and can be removed by the addition of thiols.