| Institution: | (1) Biosciences, Argonne National Laboratory, Structural Biology Center, Midwest Center for Structural Genomics, 9700 South Cass Avenue, 60439 Argonne, IL, USA;(2) Present address: GM/CA Collaborative Access Team, Argonne National Laboratory, USA;(3) Clinical Genomics Center, University Health Network, 101 College Street, M5G 1L7 Toronto, Ontario, Canada;(4) Argonne National Laboratory, Structural Biology Center, 9700 South Cass Avenue, 60439 Argonne, IL, USA;(5) Banting and Best Department of Medical Research, University of Toronto, 112 College Street, M5G 1L6 Toronto, Ontario, Canada;(6) Structural Genomics Consortium, University of Toronto, 112 College Street, M5G 1L6 Toronto, Ontario, Canada;(7) Department of Medical Biophysics, University of Toronto, 610 University Avenue, M5G 2M9 Toronto, Ontario, Canada;(8) Department of Botany, University of Toronto, 25 Wilcocks Street, M5S 3B2 Toronto, Ontario, Canada;(9) Present address: GM/CA Collaborative Access Team, Biosciences, Argonne National Laboratory, USA |
| Abstract: | The crystal structure of the hypothetical protein TA1238 from Thermoplasma acidophilum was solved with multiple-wavelength anomalous diffraction and refined at 2.0  resolution. The molecule consists of a typical four-helix antiparallel bundle with overhand connection. However, its oligomerization into a trimer leads to a  coiled super-helix which is novel for such bundles. Its central feature, a six-stranded coiled coil, is also novel for proteins. TA1238 does not have strong sequence homologues in databases, but shows strong structural similarity with some proteins in the Protein Data Bank. The function could not be inferred from the sequence but the structure, with some rearrangement, bears some resemblance to the active site region of cobalamin adenosyltransferase (TA1434). Specifically, TA1238 retains Arg104, which is structurally equivalent to functionally critical Arg119 of TA1434. For such conformational change, the overhand connection of TA1238 might need to be involved in a gating mechanism that might be modulated by ligands and/or by interactions with the physiological partners. This allowed us to hypothesize that TA1238 could be involved in cobalamin biosyntheses |
