Thursday, July 27, 2006


Secrets of a Cellular Machine

Kenneth Downing and Haixin Sui of Berkeley Lab's Life Sciences Division have pioneered the use of cryo-electron tomography to examine the ubiquitous protein structures called axonemes, which form the cores of the cilia and flagella of eukaryotic cells.

Axonemes are some of nature's largest molecular machines. Their principal structural elements are microtubules, tough and versatile protein assemblies that perform many cellular roles, notably as major components of the cell skeleton. In 1998 Downing and Eva Nogales, then a scientist in his group, with colleague Sharon Wolf, first revealed the structure of alpha and beta tubulins, the protein dimers from which microtubules are constructed. In 2002 Downing and Huilin Li, also a scientist in his group, published details of a microtubule's structure at eight-angstrom resolution, better than twice that ever obtained before.

"In the present work Haixin Sui and I were initially looking to follow up the earlier work on tubulin," Downing says. "In mammals tubulin comes in many forms, so we intended to isolate the simple form in sea urchin eggs in hopes of making better crystals. It turned out that we also collected a lot of sea urchin sperm, which are an excellent source of axonemes.

[The above is based on "Molecular architecture of axonemal microtubule doublets revealed by cryo-electron tomography," by Haixin Sui and Kenneth H. Downing, which can currently be downloaded from here.]

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