Category Archives: Structure determination

A proteinaceous biomagnet?

Magnetism is helping animals to find their destinations, it does not matter whether they are very large like whales, small  like pigeon, or very tiny like butterflies  or bees, they are all dependent on the Earth magnitic field. The underlying mechanism how a magnetic field is recognized in biological terms is almost not understood.

It has been found already that the cryptochromes (Cry) have a role in magnetic reception since Cry-negative Drosophila loose their sensitivity to magnetic fields (see Gegear, R. J., Casselman, A., Waddell, S. & Reppert, S. M. Cryptochrome mediates light-dependent magnetosensitivity in Drosophila. Nature 454, 10141018 (2008)). Crytochromes are part of the intrinsic circadian clock, which resides in the human brain in the Suprachiasmatic Nucleus of the hypothalamus.

A group from Bejing has now presented a debated paper in Nature Materials that claims to have discovered a protein structure that is able to measure the magnetic field. The group around Can Xie has found that the Drosophila protein CG8198 forms complexes with FAD and Cry that establish a biomagnet. This is an astonishing piece of work. It is much debated, for example, for quantitative reasons: magnets have many more iron molecules to be seen orientating according to the field around. These tiny magnets which are in single cells, intracellular not intercellular, do not seem to have the effect necessary to communicate a message about the orientation. Whether this or the contrary will be confirmed by independent experiments, you can only guess. One could guess that cell cooperation will help to make the output from single cells large enough to become relevant. Nature there is a News & Yiews article about this paper, which is also worth reading.

This is very exciting and should be followed-up. Highly recommended!

Dechlorination — how it works

In Science this week there is a paper by Brommer et al. from Berlin and Jena, Germany, who reports the structure of the enzyme dehalogenase from
Sulfurospirillum multivorans in complex with trichlorethane and a pseudo-vitamine B12 providing the cobalt ion for electron transfer. A Perspectives article by E.A. Edwards further explains the findings: the pseudo-vitamine B12 is protected from the outside by the dehalogenase and a channel of open for the substrate and its analog.

The immune system in jawless fish

That sharks share the antibody structure with men is already known for quite some time. Whether other animals, earlier in evolution, have also antibodies and T cells like ourselves has been a open question. The answer is yes, but….

An article in PNAS from the Max-Planck-Institute for Immunobiology, Freiburg, Germany (with contributions from the Emory Univ. Atlanta, the Univ. of Maryland and from National Library of Medicine, NIH) reports in detail about one (of three) antigen receptors in lampreys. These jawless fishes (whether they belong to vertebrates is open to discussion) have a repertoire of different receptors, but unlike antibodies where the variable region is composed of variable and constant elements and linked by diversity and joining elements they are build of a variable number of leucin-rich repeats which form a structure which is reminescent of glycoprotein receptors with a very similar organization: Continue reading The immune system in jawless fish

A Structure for NO Synthase

The NO synthases structures have been elusive so far. As these are fairly complex structures with different functional domains this is not very surprising. The role of these molecules in signal transduction is established and errors therein might lead to hypertension, erectile dysfunction, neurodegeneration, stroke or heart disease.

A PNAS paper this week has solved all the three structures of eNOS, iNOS, and nNOS. They used a high through put Electron microscopy single particle method to obtain the many different conformation in which these enzyme occurs. They have also solved the role of calmodulin in the enzymatic reaction and shown why the binding of calmodulin is a time limiting step (for two of the enzymes). Given the complexity of the molecular structures shown and the different confirmation obtained this is some nice piece of work: from the structure to the function. Beautifully done!