TITLE:

AN INTEGRATIVE APPROACH TO UNDERSTANDING A MOLECULAR MOTOR

DATE:

Friday, March 20th, 2009

TIME:

3:30 PM

LOCATION:

GMCS 214

SPEAKER:

Sanford I. Bernstein, Department of Biology, San Diego State University

ABSTRACT:

We use Drosophila melanogaster, the common fruit fly, to investigate the mechanisms by which different versions of the myosin molecular motor contribute to muscle-specific cyto-architectures and contractile properties. We express various versions of myosin in transgenic indirect flight muscles and then use computational approaches to examine  1) the biochemical and biophysical properties of the myosin (ATPase, in vitro actin sliding, step size and structure of the isolated myosin), 2) the cell biology and physiology of the muscles (ultrastructure and mechanical properties), and 3) the locomotory abilities of the transgenic organisms. We found that isoform-specific differences in myosin cause relatively small structural variations in muscle assembly, but are critical to muscle stability and function. ATPase, in vitro motility and fiber mechanical assays show that embryonic and indirect flight muscle myosins are slower and faster, respectively. We constructed a series of chimeric transgenes to study the function of the alternative domains that vary between the embryonic and flight muscle Drosophila myosins. We found that one particular domain, the converter, is a key determinant of isoform-specific properties. Using cryoelectron microscopy and image reconstruction as well as molecular modeling, we find that the different converter domains of the two myosins have different structural properties. We are also using a computational approach to test the effects of myosin mutations on fly heart function. One mutation with increased molecular function yields restrictive cardiomyopathy whereas one with decreased molecular function leads to dilated cardiomyopathy. These phenotypes parallel those arising from myosin mutations in humans. Drosophila may thus serve as a useful model for studying the molecular basis of cardiomyopathy, as well as mechanisms of its suppression. Finally, we are studying a molecular chaperone, UNC-45, that appears to be critical for stabilizing myosin during muscle stress. In collaboration with Tom Huxford (Chemistry and Biochemistry Dept.), we are solving the structure of this new class of myosin binding proteins.

HOST:

Paul Paolini

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