2009年03月12日

STRUCTURL BIOLOGY : Molecular mecanichnery in action

If biology were a car, structural biologists would be looking under the bonnet to find out how the engine works.

Put more prosaically, structural biology aims to understand how biology works at the molecular level.

Much information is gleaned by studying at atomic resolution the three-dimensional structurs of molecules that make up living organisms, and the interactions of these molecules with one another.


### DataBace ###
nature Vol.445 567-682 Issue no.7128 8 Febuary 2007
News and Views p.609 / STRUCTURL BIOLOGY : Molecular mecanichnery in action / Ad Bax and Dennis A. Torchia
Articles p.618 / Quantitative dynamics and binding studies of the 20S proteasome by NMR / R Sprangers & L E Kay (The Universuty of Tronto)


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2009年03月03日

Structural basis for messenger RNA movement on the ribosome

Translation initiation is a major determinant of the overall expression level of a gene.(Gold,L. Posttranscriptional regulatory mechanisms in Escherichia coli. Annu. Rev. Biochem 57,199-233/1988)(Draper,D.E. in Eschericha coli and Salmonella : Cellular and Moecular Biology 2nd edn /eds Neidhardt,F.C. et al./902-908/ASM Press, Washington,DC,1996/)(Kozak,M. Regulation of translation via mRNA structure in prokaryotes and eukaryotes. Gene 361,13-37/2005)

The translation of functionally active protein requires the messenger RNA to be positioned on the ribosome such that the syart/initiation codon will be read first and in the correct frame.

Little is Known about the molecular basis for the interaction of mRNA with the ribosome at different states of translation.

Recent crystal structures of the ribosomal subunits (Wimberly,B.T. et al. structure of the 30S ribosomal subunit. Nature 407,327-339/2000)(Ogle,J.M. et al. Recognition of cognate transfar RNA by the 30S ribosomal subunit. Scrence 292,897-902/2001)(Ban,N. et al. The complete atomic structure of the large ribosomal subunit at 2.4 Å resolution. Science 289,905-920/2000)(Schluenzen,F. et al. Structure of functionally activated samall ribosomal subunit at 3.3 Å resolution. Cell 102,615-623/2000)(Haems,J. et al. High resolution structure of the large ribosomal subunit from a mesophilic eubacterium. Cell 107,679-688/2001), the empty 70S ribosome (Schuwirth,B.S. et al. structures of the bacterial ribosome at 3.5 Å resolution. Science 310,827-834/2005) and the 70S ribosome containing functional ligands (Yusupov,M.M. et al. Crystal structure of the ribosome at 5.5 Å resolution. Science 292,883-896/2001)(Yusupova,G.Z. et al. The path of messenger RNA through the ribosome. Cell 106, 233-241/2001)(Jenner,L. et al. Translational operator of mRNA on the ribosome : how reperssor proteins exclude ribosome binding. Science 308,120-123/2005)(Petry,S. et al. Crystal structures of the ribosome in complex with release factors RF1 and RF2 bound to a cognate stop codon. Cell 123, 1255-1266/2005) have provided information about the general organization of the robosome and its functional centres.

Hare we compare the X-ray structures of eight ribosome complexes modelling the translation initiation, post-initiation and elongation states.

In the initiation and post-initiation complexes, the presence of the Shine-Dalgarno (SD) duplex causes strong anchoring of the 5'- end of mRNA onto the platform of the 30S subunit, with numerous interactions between mRNA and the ribosome.

Conversely, the 5' end of the 'elongator' mRNA lacking SD interctions is flexible, suggesting a different exit path for mRNA during elongation.

After the initiation of translation, but while an SD interaction is still present, mRNA moves in the 3'→5' direction with simultaneous clockwise rotation and lengthening of the SD duplex, bringing it into contact with robosomal protein S2.


### DataBace ###
nature Vol.444 243-400 Issue no.7117 16 November 2007
Letters p.391 / Structural basis for messenger RNA movement on the ribosome / G Yusupova et al. (IGBMC)


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STURUCTUAL BIOROGY : Dangerros liaisons on newrons

Crystal structures show that botulinum toxins bind simultaneously to two sites on neurons. This dual interaction allows them to use a trojan-horse strategy to enter nerve terminals, with deadly effect.

Botulinum neurotoxins (BoNTs) are some of the most deadly substances known to mankind. By blocking nerve function, they cause botulism, a severe condition that may ultimately lead to muscular and respiratory paralysis.

These sophisticated bacterial proteins owe their toxicity to their extraordinary specificity for neurons and to their enzymatic activity.

In this issue, papers by Jin et al. and Chai et al. describe the mechanisms by which BoNT/B - a toxin that causes human botulism - recognizes the surface of neuron junctions(syn apses - * This article and the papers concerned -were published online on 13 December 2006).(Jin,R., Rummel,A. Binz,A.T. Nature 444,1092-1095/2006)(Chai,Q. et al. Nature 444,1096-1100/2006)

This work provides insight in to how other BoNTs may exert their lethal action, and describes a mode of binding that night be used by other biological compounds.

Once inside a neuron, a single molecule of BoNT is, in principle, capable of deactivating the whole synapse. NoNTs consist of two protein segments, known, as the heavy and light chains.

IT is the light chain that deactivates neuromuscular junctions - the synapses that connect muscles to their contorolling neurons - by specifically inhibiting members of the SNARE protein family.(Schiavo,G., Matteoli, M. & Montecucco,C. Physiol. Rev. 717-766/2000).

SNARE proteins are distributed over the membranes of all animal and plant cells and are also found on the membranes of synaptic vesicles, the bubble-shaped organelles that store and release neurotrans-mitter chemicals at neuron terminals.

SNARE proteins are essential for membrane fusion, during which vesicles merge with the cell membrane and release their load. Once the synapticvesicles have done this, they are recycled by the neuron for further use.


### DataBace ###
nature Vol.444 243-400 Issue no.7117 16 November 2007
News and Vews p.1019/ STURUCTUAL BIOROGY : Dangerros liaisons on newrons / Giampietro Schiavo
Letters p.1092 / Botulinum newrotoxin B recognizes its protein receptor with high affinity and specificity / R Jin et al. (Stanfoed University)
Letters p,1096 / Structural basis of cell surface receptor recognition by botulinum newrotoxin B / Q Chai et al. (Scripps Research Institute)

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