Microtubule binding and translocation by inner dynein arm subtype i1

Publisher Website
Google Scholar
Abstract
Structural, biochemical, and genetic evidence has demonstrated there are three inner dynein arm subforms, I1, I2, and I3, which differ in organization and composition (see Piperno et al.: J. Cell Biol. 110:379–389, 1990). Using dynein extracted from Chlamydomonas outer dynein armless mutant pf28, we have begun to define the structural and functional properties of isolated inner arm subforms. Inner dynein arm I1 was purified either by sucrose density gradient centrifugation or microtubule binding affinity. I1, composed of heavy chains 1α and 1β, sedimented at 21S and selectively bound to and cross‐linked purified microtubules in and ATP‐sensitive manner. Deep etch electron microscopy revealed that the 21S sedimenting fraction contained two‐headed structures in which large globular heads are connected by long, flexible‐stem domains. In contrast, components derived from I2 and I3 sedimented as a mixture of 11S particles with single globular heads which did not bind to purified microtubules. Both the 21S and 11S sedimenting fractions supported microtubule translocation in in vitro motility assays. In 1 mM MgATP the I1‐containing fraction produced very slow microtubulegliding velocities (0.76 μm/sec) compared to the I2, I3‐containing fraction (4.1 μm/sec).