ATP-insensitive interaction of the amino-terminal region of the beta heavy chain of dynein with microtubules.

The ATP-insensitive microtubule-binding site of dynein has been investigated by limited proteolysis of sea urchin sperm flagellar axonemes. Mild tryptic digestion cleaved the dynein beta chain at either of two principal cleavage sites, generating two sets of complementary peptides. Inclusion of ATP in the digestion medium had no effect on the generation of these primary fragments. Sucrose density gradient separation and immunostaining with monoclonal antibodies against epitopes on the beta chain showed that extraction of the digested axonemes with 1-3 mM ATP solubilizes the peptides located at the carboxy-terminal end of the original heavy chain. The solubilization of the peptides containing the amino end required the presence of 0.6 M NaCl and was not affected by ATP. While the outer arm dynein is in situ on the axoneme, the N-terminal 125-kDa domain of the beta chain was not digested by trypsin, whereas in soluble dynein this domain becomes rapidly degraded. These data suggest that the N-terminal domain of the beta chain is involved in its ATP-insensitive attachment to microtubules and support the hypothesis that the N-terminal 125-kDa peptide corresponds to the flexible tail of the dynein molecule seen in electron micrographs.