Reporter 454, 19 June 2000

Big steps for a molecule

Structural biologists in the University’s Astbury Centre and School of Biomedical Sciences have come up with an explanation of how myosins, the motor proteins in cells, manage to transport chemical cargoes along actin filaments in nerve cells - by molecules ‘walking’ in a straight line.

Watch closely: Leeds biologists John Trinick, Matt Walker, Stan Burgess and Peter Knight at the electron microscope

In a paper in the current issue of Nature, Matthew Walker, Stan Burgess, John Trinick and Peter Knight report how they used electron microscopy to identify how individual twin-headed molecules of myosin V, a protein particularly common in nerve cells, move along the helical structure of the underlying protein, actin.

In muscle tissues, the heads of a similar protein, myosin II, are so short that they move around the helix of the actin rather than straight along it. Myosin V, however, has longer heads - measuring about 31 nanometres (millionths of a millimetre) - and thus can take longer strides.

The researchers filmed myosin V molecules ausing the actin fibre as rails, along which they move by attaching one of their heads to it and swinging the other one in front to attach further along. This repeated action is how the myosin ‘motors’ messages along the nerve fibre.

Closer examination showed that the distance between one of these attachments and the next is 36 nm - matching that between one twist and the next in the actin corkscrew. A series of strides of this size will move the myosin in a straight line instead of curling around the actin filament.

Of wider significance, however, is that the shapes of the two attached heads are different. One resembles a well-studied structure present in muscle in rigor mortis, but the other is new and appears to be the long-sought structure which precedes the power stroke of the motor. This opens the way to a fuller understanding of motor function in all myosins.

Co-authors of the paper are James Sellers, Fei Wang and John Hammer of the US National Institutes of Health in Maryland.

To view the article in Nature see their website:

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