Actin-actin and actin-deoxyribonuclease I contact sites in the actin sequence

Actin subunits in F-actin were cross-linked with m-maleimidobenzoyl N-hydroxysuccinimide ester (MBS). Peptide maps of the cross-linked actin dimer have revealed that the attachment sites of the MBS cross-link in actin are Cys-373 and a lysine residue in the CB-17 segment (Lys-191, Lys-213, or Lys-215). Since MBS spans approximately 8 A, the result indicates that Cys-373 in an actin subunit is within the distance of approximately 8 A from the lysine residue in the neighboring actin subunit. Therefore, it seems that Cys-373 and the lysine residue in the CB-17 segment are close to the regions of the actin-actin contact sites. The actin-DNase I complex was cross-linked with 1,5-difluoro-2,4-dinitrobenzene ( FFD ). Peptide maps of the actin-DNase I cross-linked complex have shown that the attachment site of the FFD cross-link in actin is in its CB-10 segment. The CB-10 segment of actin contains Lys-50, Lys-61, Lys-68, Tyr-53, and Tyr-69 as candidates for the attachment site. FFD can span only 3 A, and therefore it is most likely that one of these residues is in the region of the binding site of DNase I in actin.