A refined model for the solution structure of oxidized putidaredoxin.

A refined model for the solution structure of oxidized putidaredoxin (Pdxo), a Cys4Fe2S2 ferredoxin, has been determined. A previous structure (Pochapsky et al. (1994) Biochemistry 33, 6424-6432; PDB entry ) was calculated using the results of homonuclear two-dimensional NMR experiments. New data has made it possible to calculate a refinement of the original Pdxo solution structure. First, essentially complete assignments for diamagnetic 15N and 13C resonances of Pdxo have been made using multidimensional NMR methods, and 15N- and 13C-resolved NOESY experiments have permitted the identification of many new NOE restraints for structural calculations. Stereospecific assignments for leucine and valine CH3 resonances were made using biosynthetically directed fractional 13C labeling, improving the precision of NOE restraints involving these residues. Backbone dihedral angle restraints have been obtained using a combination of two-dimensional J-modulated 15N,1H HSQC and 3D (HN)CO(CO)NH experiments. Second, the solution structure of a diamagnetic form of Pdx, that of the C85S variant of gallium putidaredoxin, in which a nonligand Cys is replaced by Ser, has been determined (Pochapsky et al. (1998) J. Biomol. NMR 12, 407-415), providing information concerning structural features not observable in the native ferredoxin due to paramagnetism. Third, a crystal structure of a closely related ferredoxin, bovine adrenodoxin, has been published (Müller et al. (1998) Structure 6, 269-280). This structure has been used to model the metal binding site structure in Pdx. A family of fourteen structures is presented that exhibits an rmsd of 0.51 A for backbone heavy atoms and 0.83 A for all heavy atoms. Exclusion of the modeled metal binding loop region reduces overall the rmsd to 0.30 A for backbone atoms and 0.71 A for all heavy atoms.

Interpreting elbow radiographs in children.

Accurate diagnosis of elbow fractures in children requires knowledge of anatomic development. The multiple ossification centers in the elbow can be mistaken for fractures, making radiographic diagnosis difficult. Anteroposterior and lateral radiographs are most commonly used, although oblique views may help in the detection of subtle injuries. Comparison views of the uninjured elbow are of questionable value. Anterior and posterior fat pad signs indicate joint effusion, which suggests significant trauma. Intersection of the anterior humeral and central radial lines can be used to assess joint alignment. Fractures displaced less than 2 mm are considered stable and may be treated conservatively.

Redox-dependent dynamics of putidaredoxin characterized by amide proton exchange.

Multidimensional NMR methods were used to obtain 1H-15N correlations and 15N resonance assignments for amide and side-chain nitrogens of oxidized and reduced putidaredoxin (Pdx), the Fe2S2 ferredoxin, which acts as the physiological reductant of cytochrome P-450cam (CYP101). A model for the solution structure of oxidized Pdx has been determined recently using NMR methods (Pochapsky TC, Ye XM, Ratnaswamy G, Lyons TA, 1994, Biochemistry 33:6424-6432) and redox-dependent 1H NMR spectral features have been described (Pochapsky TC, Ratnaswamy G, Patera A, 1994, Biochemistry 33:6433-6441). 15N assignments were made with NOESY-(1H/15N) HMQC and TOCSY-(1H/15N) HSQC spectra obtained using samples of Pdx uniformly labeled with 15N. Local dynamics in both oxidation states of Pdx were then characterized by comparison of residue-specific amide proton exchange rates, which were measured by a combination of saturation transfer and H2O/D2O exchange methods at pH 6.4 and 7.4 (uncorrected for isotope effects). In general, where exchange rates for a given site exhibit significant oxidation-state dependence, the oxidized protein exchanges more rapidly than the reduced protein. The largest dependence of exchange rate upon oxidation state is found for residues near the metal center and in a region of compact structure that includes the loop-turn Val 74-Ser 82 and the C-terminal residues (Pro 102-Trp 106). The significance of these findings is discussed in light of the considerable dependence of the binding interaction between Pdx and CYP101 upon the oxidation state of Pdx.

A structure-based model for cytochrome P450cam-putidaredoxin interactions.

Putidaredoxin (Pdx) is a Fe2S2 ferredoxin which acts as the physiological reductant of cytochrome P-450cam (CYP101). A model for the solution structure of oxidized Pdx has been determined using NMR methods (Pochapsky et al (1994) Biochemistry 33, 6424-6432). 1H-15N correlations and redox-dependent amide exchange rates have also been described (Lyons et al (1996) Protein Sci 5, 627-639). Data obtained from mutagenesis and kinetic measurements concerning the interactions of Pdx and CYP101 are summarized. A model for the structure of the homologous ferredoxin adrenodoxin (Adx) is also described, and data concerning Adx activity are discussed in relation to this structure. The structures of Pdx and CYP101 were used as starting points for molecular modeling and molecular dynamics simulations. Close approach between the metal centers of the two proteins and interaction between aromatic residues on the surfaces of the proteins are premised. The resulting complex exhibits three intermolecular salt bridges, five intermolecular hydrogen bonds and a 12 A distance between the metal centers. The first direct observations of interaction between Pdx and CYP101 (by two-dimensional NMR of 15N-labeled Pdx in solution with CYP101) are described. The results of the NMR experiments indicate that conformational gating of the electron transfer complex between CYP101 and Pdx may be important.

An NMR-derived model for the solution structure of oxidized putidaredoxin, a 2-Fe, 2-S ferredoxin from Pseudomonas.

A model for the solution structure of oxidized putidaredoxin (Pdx), a 106-residue globular protein containing a Fe2S2 cluster, has been determined using homonuclear NMR methods. Pdx is the first of the class of Fe2S2Cys4 ferredoxins which act as electron-transfer partners for P-450 monooxygenases to be structurally characterized, and no crystal structure has been determined for Pdx or for any closely homologous protein. Pdx is the physiological redox partner of cytochrome P-450cam. A total of 878 NOE distance constraints, 66 phi angular constraints derived from NH-C alpha H coupling constants, and five paramagnetic broadening constraints were used in simulated annealing structural refinements to obtain a family of structures with pairwise rms deviations of 1.14 A for backbone atoms and 1.80 A for all non-hydrogen atoms. Paramagnetic broadening of resonances within a ca. 8-A radius of the metal cluster prevents the use of NMR-derived constraints in this region of the protein; structural constraints used to model the environment of the metal cluster were obtained from site-directed mutagenesis and model compounds and by comparison with known ferredoxin structures. Pdx retains a similar folding topology to other structurally characterized Fe2S2Cys4 ferredoxins but differs from the other ferredoxins in containing a significantly more compact structure in the C-terminal half of the protein.

Neurosecretion of arginine vasopressin by an olfactory neuroblastoma causing reversible syndrome of antidiuresis.

A 26-year-old woman with the syndrome of inappropriate antidiuresis demonstrated complete recovery following the resection of an olfactory neuroblastoma. Tissue arginine vasopressin levels by radioimmunoassay, immunohistochemical staining of the tissue arginine vasopressin, postoperative normalization of plasma arginine vasopressin levels, and the clinical resolution are evidence in support of a neurally derived tumor being the direct source of neurosecretion of arginine vasopressin rather than neurohypophyseal secretion or secretion from non-neural tissues, as reported to date in the etiology of the syndrome of inappropriate antidiuresis.

Diagnosis of non-Hodgkin's lymphoma intracerebral mass lesions. Usefulness of Tc-99m pertechnetate and Ga-67 citrate brain scans.

This paper summarizes the clinical and diagnostic features of five reports of patients with intracerebral, non-Hodgkin's lymphoma. In three patients the brain lesion was the only evidence of lymphoma, while two patients also had concomitant systemic involvement. Four patients had diffuse histiocytic lymphoma and one had a mixed type of malignant lymphoma. In all patients, Tc-99m and Ga-67 brain scans disclosed discrete areas of increased radionuclide uptake consistent with a mass. In each case, brain blood perfusion studies were normal and brain computerized tomographic (CT) scans and cerebral angiograms produced variable nondiagnostic patterns. Craniotomies in four patients provided histologic confirmation of the non-Hodgkin's lymphoma in the areas of abnormality. The remaining patient had systemic histiocytic lymphoma with concomitant brain lesions that responded to irradiation. The combined use of the above noninvasive modalities in correlation with clinical findings may result in more accurate prebiopsy diagnoses of intracerebral lymphoma.

External ventricular drainage. A technical note.

The disadvantages of external ventricular drainage are the threat of sepsis and the nuisance of dislodging a precarious system in routine care. The experience of the authors with nearly 200 cases using a long ventricular catheter demonstrates that a subgaleal tunnel can be easily made for the ventricular catheter using a sharp trocar. The resulting system is secured by the tunnel, easily dressed, and has a minimal likelihood of sepsis. Although external drainage has been maintained for longer than 3 weeks in some cases, the average duration is 6 days; and in the last 68 cases, there has been no incidence of sepsis and but one case of patient removal of the catheter. The device has been used for both monitoring, as well as ventricular decompression in a broad range of patients.