Structure of the alpha and beta heavy chains of the outer arm dynein from Chlamydomonas flagella. Location of epitopes and protease-sensitive sites

We describe here the pathways by which the alpha and beta heavy chains of the outer arm dynein from Chlamydomonas flagella are degraded by endoproteases. By probing the digestion products with monoclonal antibodies, we have located a number of protease-sensitive sites within both polypeptides and identified the regions of each molecule from which specific fragments are derived. These data also define the regions within each chain which contain the epitopes recognized by our monoclonal antibodies. The locations of the cleavage sites reveal both differences and similarities between the two molecules. The sites at which the beta chain is initially cleaved by elastase differ depending upon whether the particle is digested in situ or in solution, indicating that the beta chain undergoes a significant conformational change following extraction from the axoneme. Evidence was also obtained that heterogeneity exists among the purified alpha chain molecules. The possible arrangement of the different regions of the heavy chains within the alpha-beta dimer is discussed.