This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Portal proteins are large oligomeric DNA pumps, which connect the icosahedral capsid of tailed bacteriophages to the viral tail. Despite the large size and complex structural organization, portal proteins are formed by a single polipeptide chain that self assembles to yield a dodecameric ring. We have studied the portal protein of bacteriophage P22, which is formed by 12 subunits of ~ 83KDa (overall M.W.~1MDa). We have crystallized the full length 1MDa ring as well as two large C-terminally truncated fragments of the protein spanning residues 1-627 and 1-602 (named C(1-627) and C(1-602), respectively). Whereas full-length P22 portal protein crystals diffract X-rays poorly (7 at best), complete diffraction data to 3.85 have been measured for the C-terminal deletion fragment C(1-602). We have now obtained large crystals (up to 0.7 mm) of seleno-methionine derivatized C(1-602) P22 portal protein, which, hopefully, will enable to carry out a complete MAD experiment. In addition, in collaboration with Prof Sherwood Casjens, we have expressed and purified the P22 tail accessory factors gp4, gp10, and gp26, which we are trying to crystallize in complex with the P22 portal protein. The long-term goal of this project is to determine the crystal structure of the entire P22 DNA packaging/tail machine.
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