Interaction of 75-106 actin peptide with myosin subfragment-1 and its trypsin modified derivative

To explore the role of a hydrophobic domain of actin in the interaction wit h a myosin chain we have synthesized a peptide corresponding to residues 75 -106 of native actin monomer and studied by fluorescence and ELISA the inte raction (13 +/- 2.6 x 10(-6) M) with both S-l and (27 kDa-50 kDa-20 kDa) S- l trypsin derivative of myosin. The loop corresponding to 96-103 actin resi dues binds to the S-l only in the absence of Mg-ATP and under similar condi tions but not to the trypsin derivative S-l. Biotinylated C74-K95 and I85-K 95 peptide fragments were purified after actin proteolysis with trypsin. Th e C74-K95 peptide interacted with both S-l and the S-l trypsin derivative w ith an apparent K-d(app) of 6 +/- 1.2 x 10(-6) M in the presence or absence of nucleotides. Although peptide fragment I85-K95 binds to S-l with a K-d( app) of 12 +/- 2.4 x 10(-6) M, this fragment did not bind to the trypsin S- l derivative. We concluded that the actin 85-95 sequence should be a potent ial binding site to S-l depending of the conformational state of the intact 70 kDa segment of S-l. (C) 1999 Elsevier Science B.V. All rights reserved.