The cell cycle regulatory tumor suppressor proteins p53 and pRB are targeted for inactivation by several tumor viruses, including the high-risk types of human papillomaviruses (HPVs) via interactions of the HPV E6 and E7 oncoproteins with p53 and pRB, respectively. p53 plays a central role in a signal transduction pathway that mediates G, arrest after DNA damage, though the mechanism by which G, arrest occurs has not been elucidated. The cyclin-associated protein p2lwan/dPl has recently been shown to be induced by
The structures of the dinuclear Ni(II) active sites of urease from jack bean and Klebsiella aerogenes are compared with and without the addition of the inhibitor 2-mercaptoethanol (2-ME). No significant differences are observed by nickel K-edge X-ray absorption spectroscopy between the plant and bacterial enzymes. The Ni X-ray absorption edge spectra display an 8332-eV Is -*• 3d peak intensity similar to that observed for five-coordinate Ni(II) compounds1 for both native and 2-ME-bound derivatives. Curve-fitting of Ni EXAFS data indicates that the average Ni(II) coordination environment in native urease can be described as Ni(imidazole)x(N,0)5_x, with x = 2 or 3. Addition of 2-ME results in replacement of one of the non-imidazole (N,0) ligands with (S,C1) (most likely the thiolate sulfur of 2-ME) and results in the appearance of a new peak in the Fourier transforms that can only be fit with a Ni-Ni scattering component at a Ni-Ni distance of ~3.26 Á. A structure for this 2-ME-bound dinuclear site is proposed to contain the two Ni(II) ions bridged by the thiolate sulfur of 2-ME.revealed the presence of weak d-d absorption bands (Xmax at 407, 745, and 1060 nm) that were consistent with octahedral Ni-
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