Browsing by Author "Bhati, M"

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    Fe and Mg solubility in the Ca site of zirconolite, CaZrTi2O7
    (Australian Institute of Physics, 2004-02-04) Vance, ER; Cashio, JG; Hanna, JV; Garrett, Z; Bhati, M
    The solid solubility of Fe in the Ca site of zirconolite appears to be approximately the same whether it is incorporated as the divalent or trivalent species. Divalent Fe was encouraged by using an argon firing atmosphere and direct substitution in the Ca site [Ca(1-x)FexZrTi2O7] and trivalent Fe by the use of an air atmosphere and Al compensation in the Ti site [Ca(1-x)FexZrTi(2-x)AlxO7]. The anticipated valences were confirmed by X-ray near-edge, Xray photoelectron and Mossbauer spectroscopies. Changing the firing atmosphere from argon to air and vice versa also changed the Fe valences, but scanning electron microscopy showed that small amounts of second phase, Fe-bearing materials were present. The possible reasons for the apparently similar solid solubilities of divalent and trivalent Fe in the Ca site are discussed. Solid state magic-angle nuclear magnetic resonance was used to study Mg speciation in the Ca and Ti sites of zirconolite.
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    Solution structure of the LIM-homeodomain transcription factor complex Lhx3/Ldb1 and the effects of a pituitary mutation on key Lhx3 interactions
    (Public Libary of Science, 2012-07-25) Bhati, M; Lee, C; Gadd, MS; Jeffries, CM; Kwan, AH; Whitten, AE; Trewhella, J; Mackay, JP; Matthews, JM
    Lhx3 is a LIM-homeodomain (LIM-HD) transcription factor that regulates neural cell subtype specification and pituitary development in vertebrates, and mutations in this protein cause combined pituitary hormone deficiency syndrome (CPHDS). The recently published structures of Lhx3 in complex with each of two key protein partners, Isl1 and Ldb1, provide an opportunity to understand the effect of mutations and posttranslational modifications on key protein-protein interactions. Here, we use small-angle X-ray scattering of an Ldb1-Lhx3 complex to confirm that in solution the protein is well represented by our previously determined NMR structure as an ensemble of conformers each comprising two well-defined halves (each made up of LIM domain from Lhx3 and the corresponding binding motif in Ldb1) with some flexibility between the two halves. NMR analysis of an Lhx3 mutant that causes CPHDS, Lhx3(Y114C), shows that the mutation does not alter the zinc-ligation properties of Lhx3, but appears to cause a structural rearrangement of the hydrophobic core of the LIM2 domain of Lhx3 that destabilises the domain and/or reduces the affinity of Lhx3 for both Ldb1 and Isl1. Thus the mutation would affect the formation of Lhx3-containing transcription factor complexes, particularly in the pituitary gland where these complexes are required for the production of multiple pituitary cell types and hormones. © 2012 Bhati et al.