Literature

Animations of the kinesin motor protein have captured something of the astounding orchestration of processes within the cell. We already know quite a lot about the microtubules on which kinesin “walks”. Protofilaments made of tubulin assemble to form a sheet which then folds to form the microtubule structure. The join of the two edges of the sheet has not been previously considered very interesting. Andreas Hoenger is quoted as saying: "Until now the function of the seam has been unknown and it has been largely ignored as an odd and irrelevant part of the microtubule lattice. Our experiments now reveal it as a central spot where microtubule stability can be regulated."
New research has identified a protein Mal3p that plays a crucial role in assembly of the microtubules, described as a molecular “zipper”. Cellular controls on this protein lead to assembly, disassembly and rapid switching. There are indications that the same protein “could also play a more active role in transportation”. A remarkable photograph of an opening microtubule is here.
Although the new studies have involved yeast cells, the Mal3p protein is widely found in different organisms, and the results are considered likely to be of general relevance.
Every new advance in understanding the molecular machines within the cell reveals complex specified information and strengthens the case for ID.

The Schizosaccharomyces pombe EB1 Homolog Mal3p Binds and Stabilizes the Microtubule Lattice Seam
Linda Sandblad, Karl Emanuel Busch, Peter Tittmann, Heinz Gross, Damian Brunner, and Andreas Hoenger
Cell, 127(7), 29 December 2006, Pages 1415-1424

Summary: End binding 1 (EB1) proteins are highly conserved regulators of microtubule dynamics. Using electron microscopy (EM) and high-resolution surface shadowing we have studied the microtubule-binding properties of the fission yeast EB1 homolog Mal3p. This allowed for a direct visualization of Mal3p bound on the surface of microtubules. Mal3p particles usually formed a single line on each microtubule along just one of the multiple grooves that are formed by adjacent protofilaments. We provide structural data showing that the alignment of Mal3p molecules coincides with the microtubule lattice seam as well as data suggesting that Mal3p not only binds but also stabilizes this seam. Accordingly, Mal3p stabilizes microtubules through a specific interaction with what is potentially the weakest part of the microtubule in a way not previously demonstrated. Our findings further suggest that microtubules exhibit two distinct reaction platforms on their surface that can independently interact with target structures such as microtubule-associated proteins, motors, kinetochores, or membranes.

See also:
Kikkawa, M. and Metlagel, Z. A molecular ‘zipper’ for microtubules,
Cell, Volume 127, Issue 7, 29 December 2006, Pages 1302-1304.

Roadworks on the motorways of the cell
EurekAlert, 28 December 2006.