Globin X: A highly stable intrinsically hexacoordinate globin.

Several novel members of the vertebrate globin family were recently discovered with unique structural features that are not found in traditional penta-coordinate globins. Here we combine structural tools to better understand and recognize molecular determinants that contribute to the stability of hexacoordinate globin X (GbX) from Danio rerio (zebrafish). pH-induced unfolding data indicates increased stability of GbX with pHmid of 1.9 ± 0.1 for met GbXWT, 2.4 ± 0.1 for met GbXC65A, and 3.4 ± 0.1 for GbXH90V. These results are in good agreement with GbX unfolding experiments using GuHCl, where a ΔGunf 13.8 ± 2.5 kcal mol-1 and 16.3 ± 2.6 kcal mol-1 are observed for metGbXWT, and metGbXC65A constructs, respectively, and diminished stability is measured for GbXH90V, ΔGunf = 9.5 ± 3.6 kcal mol-1. The metGbXWT and metGbXC65A also exhibit high thermal stability (melting points of 118 °C and 107 °C, respectively). Native ion mobility - mass spectrometry (IM-MS) experiments showed a narrow charge state distribution (9-12+) characteristics of a native, structured protein; a single mobility band was observed for the native states. Collision induced unfolding IM-MS experiments showed a two-state transition, in good agreement with the solution studies. GbXWT retains the heme over a wide range of charge states, suggesting strong interactions between the prosthetic group and the apoprotein. The above results indicate that in addition to the disulfide bond and the heme iron hexa-coordination, other structural determinants enhance stability of this protein.

Mononuclear, hexanuclear and polymeric indium(III) pyrazolido complexes; structural characterization, dynamic solution studies and luminescent properties.

A new family of six mononuclear indium(III) complexes of formula mer-[InIIICl3(pz*H)3]-pz*H = pyrazole (pzH), or substituted pyrazoles: 4-Cl-pzH, 4-Br-pzH, 4-I-pzH, 4-Ph-pzH and 3,5-Me2-pzH-were synthesized by addition reactions of InCl3 and pz*H and crystallographically characterized. The fluxional behaviour of the complexes, probed by variable temperature 1H NMR spectroscopy in the 328 K to 173 K range, was attributed to (at least) four simultaneous processes: pyrazole N-H proton dissociation/association, cis/trans-pyrazole exchange, and N1/N2 tautomerization of the cis- and of the trans-pyrazoles. Three novel trianionic hexanuclear complexes of general formula (pipH)3[In6Cl6(µ3-OH0.5)2(µ-OH)6(µ-pz*)6]-pz* = pz, 4-Cl-pz and 4-Ph-pz-showing µ-hydroxo and µ-oxo bridges were synthesized from the corresponding mer-[InIIICl3(pz*H)3] and characterized by single crystal X-ray diffraction and 1H NMR. Under different solvent conditions, multicolour emitting polymeric complexes of general formula [In(µ-pz*)3]n-pz* = pz, 4-Cl-pz, 4-I-pz and 4-Ph-pz-were obtained also from mer-[InIIICl3(pz*H)3] after addition of a base. Luminescence and lifetime calculations were performed for all polymers formed.