Difference between revisions of "20.109(F07): Growth of phage materials"
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[[Image:Abalone.jpg|thumb|left|200 px| Abalone shell]] | [[Image:Abalone.jpg|thumb|left|200 px| Abalone shell]] | ||
[[Image:Diatoms.jpg|thumb|right|225 px| diatoms]]<br> | [[Image:Diatoms.jpg|thumb|right|225 px| diatoms]]<br> | ||
− | The accomplishments of the natural world can inspire us to great engineering feats. Biomineralization is one particularly impressive trick nature pulls off. Vertebrates, invertebrates and plants all have ways to precisely position inorganic substrates into crystalline order. For example, calcium carbonate will form unstructured dust in the absence of genetically-programmed organizers, but the same material can be made into the hard and luminous shells of sea creatures. Similarly, diatoms organize silicon dioxide into intricate patterns that manufacturers of electronic components | + | The accomplishments of the natural world can inspire us to great engineering feats. Biomineralization is one particularly impressive trick nature pulls off. Vertebrates, invertebrates and plants all have ways to precisely position inorganic substrates into crystalline order. For example, calcium carbonate will form unstructured dust in the absence of genetically-programmed organizers, but the same material can be made into the hard and luminous shells of sea creatures. Similarly, diatoms organize silicon dioxide into intricate patterns that manufacturers of electronic components can t begin to approach. In one more instance, bacteria align iron inside their cytoplasm to form magnetic rods on the submicron scale. Even more amazing, these feats are accomplished without harsh chemicals, without extreme temperatures, and without noxious wastes that poison the nests of the organisms themselves. Humans have a lot to learn from nature s successes. In the upcoming weeks we ll use a biological character from earlier in the term, namely M13, and rely on the self-assembling coat to template a crystal of iridium oxide. The interaction of iridium with the p8 protein of the phage coat yields nanoscale-particles with useful optic properties, as we ll see (literally). |
− | [[Image:Phagefusions.png|thumb| 150 px| phage display]]Thinking back to the work we've done so far this term, there seems to be nothing in our initial studies of M13 that would lead us to believe that the phage could interact with inorganic materials. It's unlikely this phage would have run into lots of iridium in its natural environment. It seems even less likely that the phage might, by happy coincidence, bind this metal. It's in fact through some clever human intervention, namely selection through phage display, that a phage with such an unusual property was found. [http://www.dyax.com/discovery/phagedisplay.html Phage display] has been used for decades as a tool for discovery. This technique exploits natural selection and identifies functional peptide sequences that can be fused to the phage coat. Most often | + | [[Image:Phagefusions.png|thumb| 150 px| phage display]]Thinking back to the work we've done so far this term, there seems to be nothing in our initial studies of M13 that would lead us to believe that the phage could interact with inorganic materials. It's unlikely this phage would have run into lots of iridium in its natural environment. It seems even less likely that the phage might, by happy coincidence, bind this metal. It's in fact through some clever human intervention, namely selection through phage display, that a phage with such an unusual property was found. [http://www.dyax.com/discovery/phagedisplay.html Phage display] has been used for decades as a tool for discovery. This technique exploits natural selection and identifies functional peptide sequences that can be fused to the phage coat. Most often it s the p3 protein that s used for phage display because, despite the limited number of displayed peptides per phage (on the order of 5), there is enough flexibility to accommodate peptides of [http://www.neb.com/nebecomm/products/productE8101.asp 20 to 30 amino acids]. The other protein used for phage display, p8, is presented at much higher copy number per phage (on the order of 2700) but it has limited flexibilty. The semi-crystalline packing of p8 on the phage coat restricts fusions to only 4 to 6 neutral or negatively charged amino acids. For scientists who can tolerate a mix of p8 proteins on the phage coat for their work, there are phage-display variations that mix and match fusion and wild-type proteins on a phage coat, but for those who want phage of a particular form, the options are limited. |
− | Nonetheless, peptides with remarkably diverse functions have been isolated with phage display. Once the fusion site is chosen, a library of sequences encoding random peptides can be synthesized and cloned. In this way a pool of phage, each with different fusions, can be made. Finally, the phage pool can be screened for interesting behaviors or properties. Peptide-fusion proteins to p8 or p3 that include stop codons or intolerable sequences are largely lost from the population after the first round of | + | Nonetheless, peptides with remarkably diverse functions have been isolated with phage display. Once the fusion site is chosen, a library of sequences encoding random peptides can be synthesized and cloned. In this way a pool of phage, each with different fusions, can be made. Finally, the phage pool can be screened for interesting behaviors or properties. Peptide-fusion proteins to p8 or p3 that include stop codons or intolerable sequences are largely lost from the population after the first round of |