Business & Economics

1 pages

Divalent cations control the conformation of P-protein crystalloids in the phloem of legumes

of 1
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
Divalent cations control the conformation of P-protein crystalloids in the phloem of legumes
   56 Abstracts / Comparative Biochemistry and Physiology, Part B 126 2000) SI-S108 LIQUID CRYSTAL SPINNING IN NATURE D. P. Knight and F. Vollrath Liquid crystal spinning appears to be widespread in the animal kingdom, utilising protein dopes to give materials with a different secondary structures including [~-pleat, or-helix and collagen-fold. Here we give a comparative account of the spinning of two, extremely tough liquid crystal-based composite materials: the ~-pleated spider dragiine silk of orb-wch spiders and the collagenons egg case of Selachian fish. Both organisms use dopes with a bulk liquid crystalline phase containing droplets of a second immiscible phase. In both organisms, these droplets undergo flow elongation within hyperbolic extrusion dies which are convergent in the spider and divergent in the fish. The elongated droplets produced in this way may enhance toughness. The spider extrudes a Skin and Core composite with at least three, sequentially applied coatings. The fish extrudes a Sea and Island composite, the islands consisting of flat ribbons of carefully orientated collagen and the sea, small quantities of an amorphous matrix. In both organisms t~e molecules of the liquid crystalline dope orient in the die before a change in pH initiates polymerisation. In spiders, this is accompanied by a change in secondary structure of the dope protein which allows extensive formation of intevmoleeular hydrogen bonds to give rise to ~-crystallites. In contrast in the fish, the secondary stmct~e of the dope molecules does not change and extensive covalent cross-linking is used to increase the tensile strength of the material. Both ways of producing extremely tough materials have considerable biomhnetic potential. DIVALENT CATIONS CONTROL THE CONFORMATION OF P-PROTEIN CRYSTALLOIDS IN THE pIll,OEM OF LEGUMES Michael Knoblauch , Winfried S. Peters 2, Katrin Ehlers l, Aart J. E. van Bel l 1 Inst. f. Allg. Botanik u. Pflanzenphysiologie, Senckenbergstr. 17-21, D-35390 Giessen, Germany 2 AK Kinemat. Zellforsch., Biozentrum, Marie-Curie-Str. 9 D-60439 Frankfurt Main), Germany The phloem is the photo-assimilate transporting system of higher plants. It consists of specialized cells, the sieve elements, that fuse during their differentiation to form a continuous system of so-called sieve tubes. In the legume family (Fabaceae), these tubes contain elongate protein crystalloids (size approximately 25 × 5 × 5 pro) of previously unknown function. We have developed preparation methods that allow the observation of the reaction of these crystailoids to a variety of stimuli n s tu for the first time. We could demonstrate that turgor steps exceeding a specific threshold induce protein dispersal; the formerly compact erystalloids disintegrate into a disperse mass within one second, and form plugs sealing the sieve tubes. Thus, protein crystalioids might be involved in the avoidance of excessive loss of photo-assimilates following injury. Since protein crystalloid dispersal is fully reversible within minutes, it appears to be an ideal defense mechanism against rapid and transient disturbances, such as ~g. attacks by phloem-fecding aphids. During tests n v tro on isolated crystalloids we could establish that their reversible self-assembly is controlled by 2+ 2+ 2 specific divalent cations (Ca , Ca , Ba +), wheras other cations (Mg 2+, Mn z+, monovalent ones), anions, pH, temperature etc are not effective. The response can be prevented by chelating agents such as EDTA. Thus, Po protein crystalloids react reversibly to specific stimuli by a conformational change that can probably be used to perform mechanic work. They possess great technological potential as elements of micro-sensors, self-regulating f'dters or valves, etc. We will discuss aspects of both the biological function and the technological potential of this novel class of intelligent polymers .
Related Documents
View more...
We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks