An electron microscopic study of the archaeal feast/famine regulatory protein

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The archaeal feast/famine regulatory protein pot1216151 from the hyper-thermophile Pyrococcus sp. OT3 was studied using methods of cryo-electron microscopy. The protein was negatively stained using ammonium molybdate, and maintained at a liquid nitrogen temperature in amorphous ice in order to best protect the protein from electron irradiation damage. An electron microscope was operated at 200 KeV, and using a filtration device, zero-loss electrons were selectively focused. When the protein is in a ligand-bound form, formation of particles of the diameters of over 50 Å was observed. These particles have cavities at their centers, and with some of the particles components of a four-fold-symmetry were observed around the cavities. These characteristics are the same as those of a disk-like assembly formed by four dimers of pot1216151 in the crystal. When ligands binding to pot1216151 were removed by treating the disks with ammonium sulfate, they were disassembled, and thus not identified by electron microscopy. Some aspects of analyzing single particles are discussed.(Communicated by Masanori OTSUKA, M. J. A., Dec. 12, 2003)
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