Crystallization and preliminary X-ray analysis of a bacterial lysozyme produced by Streptomyces globisporus

The extracellular bacteriolytic enzyme produced by Streptomyces globisporus shows a beta-1,4-N,6-O-diacetylmuramidase activity as well as a beta-1,4-N-acetylmuramidase activity. Crystals of this enzyme have been obtained by the hanging-drop vapour-diffusion method using polyethylene glycol as a precipitant. They belong to the tetragonal space group P4(1)2(1)2, with unit-cell parameters a = 63.11 (4), c = 121.1 (1) A, diffract to at least 2.0 A resolution and are suitable for high-resolution structure analysis. The crystal structure was solved by molecular replacement using lysozyme produced by S. erythraeus as a search model. The structure refinement is now in progress.

Structure of the zinc-binding site in the crystal structure of a zinc endoprotease from Streptomyces caespitosus at 1 A resolution

A zinc endoprotease produced by Streptomyces caespitosus (ScNP) contains a H83E84TGH87VLG90LPD93-Met103 sequence. Except for D93, this amino acid sequence is the same as a characteristic consensus HEXXHXXGXXH-M motif found in one class of zinc endoprotease called 'metzincins'. We analyzed the structural and functional role of the consensus sequence located around a catalytically essential zinc ion based on the crystal structure of ScNP. The structure was determined at the highest level on resolution (1 A resolution) and accuracy among crystal structures of zinc endoproteases ever determined. The zinc ion of ScNP is tetrahedrally coordinated by three amino acid side-chains (H83, H87 and D93) and a water molecule. The distances between the zinc ion and the coordinating atoms are 2.01, 2.01 and 1.95 A for H83N epsilon, H87N epsilon and D93O delta, respectively. These distances agree very well with those normally found in crystal structures of zinc-containing small molecules in the Cambridge Structural Database. On the other hand, the distance between the zinc ion and the coordinating water molecule (1.93 A) is slightly shorter than the typical value (2.01 A) found in the database. In addition, E84O epsilon makes a short hydrogen bond to this water molecule with the distance of 2.54 A. Two hydrogen bonds (H83N delta-L102O, H87N delta-L91O) and van der Waals interactions between the side-chain of M103 and the two imidazole rings of H83 and H87 are also observed. These interactions are probably important for the imidazole rings to construct the tetrahedral coordination arrangement toward the zinc ion.

The role of structural intersubunit microheterogeneity in the regulation of the activity in hysteresis of ribulose 1, 5-bisphosphate carboxylase/oxygenase

Many enzymes are composed of subunits with the identical primary structure. It has been believed that the protein structure of these subunits is the same. Ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) comprises eight large subunits with the identical amino acid sequence and eight small subunits. Rotation of the side chains of the lysine residues, Lys-21 and Lys-305, in each of the eight large subunits in spinach RuBisCO in two ways produces microheterogeneity among the subunits. These structures are stabilized through hydrogen bonds by water molecules incorporated into the large subunits. This may cause different effects upon catalysis and a hysteretic, time-dependent decrease in activity in spinach RuBisCO. Changing the amino acid residues corresponding to Lys-21 and Lys-305 in non-hysteretic Chromatium vinosum RuBisCO to lysine induces hysteresis and increases the catalytic activity from 8.8 to 15.8 per site per second. This rate is approximately five times higher than that of the higher-plant enzyme.

Evidence for persistent expression of OX2 as a necessary component of prolonged renal allograft survival following portal vein immunization

Following portal vein (pv) pretransplant immunization of C3H mice, there is an early (within 2 days) increase in expression of the molecule OX2 seen on host dendritic cells (DC), along with increased survival of C57BL/6 renal allografts transplanted within 24 h of pv immunization. In addition, there is a marked polarization in cytokine production from lymphocytes harvested from the transplanted animals, with preferential production of IL-4, IL-10, and TGFbeta on donor-specific restimulation in vitro, and decreased production of IL-2, IFN-gamma, and TNFalpha compared with non-pv-immunized control transplanted mice. Both the increased renal allograft survival and the altered cytokine production are abolished by infusion of anti-mouse OX2 monoclonal antibody (3B6), even when antibody infusion is begun as late as 10 days following transplantation. Quantitative PCR analysis independently shows that OX2 expression is increased in the spleen and liver of transplanted mice as late as 21 days following pv immunization. In vitro studies with an OX2:Fc immunoadhesion had suggested that immunosuppression induced by this soluble form of the OX2 molecule was dependent primarily upon an early (OX2-dependent) signal. This discrepancy between in vivo and in vitro data possibly reflects a role for OX2 in the in vivo recruitment of other (immunregulatory) cells. Consistent with this hypothesis, regardless of the time (posttransplantation) of in vivo infusion of anti-OX2 antibody, within 2 days we observed a decline in the functional activity of a previously characterized immunoregulatory gammadeltaTCR(+) cell population, which can be monitored by its ability to regulate cytokine production in vitro.

Microcatheter intrathecal urokinase infusion into cisterna magna for prevention of cerebral vasospasm: preliminary report

BACKGROUND AND PURPOSE

The feasibility of preventing vasospasm by intrathecal anterograde infusion of urokinase (UK) into the cisterna magna was studied in patients with recently ruptured aneurysms who had just undergone the placement of a Guglielmi detachable coil (GDC).

METHODS

Immediately after complete embolization with the use of GDC-10 coils, 15 patients with Hunt and Hess neurological grades III and IV received 60 000 IU of UK in normal saline through a microcatheter advanced into the cisterna magna. UK infusion was repeated once or twice over a period of 2 to 3 days according to a decision based on CT evidence of a subarachnoid clot remaining in the cisterns. Before administering the last UK infusion, we obtained CT confirmation of almost complete clearance of clots in the basal cisterns.

RESULTS

In all 15 patients, the microcatheter was advanced easily into the cisterna magna by use of the over-the-wire microcatheter technique. In 8 patients who received thrombolytic therapy within 24 hours of the ictus, there was almost complete clearance of the clot in the basal cisterns within 2 days of suffering the insult. When UK was injected at 24 to 48 hours after the insult, 7 patients manifested CT evidence of clearance at the latest 4 days after suffering the insult. In all 15 patients, CT scans obtained within 24 hours of the final UK administration showed complete resolution of clots in the basal cistern and almost complete resolution of clots in the basal interhemispheric fissure and bilateral proximal sylvian fissures. Although one patient developed a transient neurological deficit, no patients manifested permanent delayed neurological deficits as a result of vasospasm. Outcome assessment according to the Glasgow Outcome Scale, no less than 3 months after GDC placement, revealed good recovery in all patients, and none developed hydrocephalus requiring a shunt procedure.

CONCLUSIONS

In patients with recently ruptured aneurysms, GDC placement followed by immediate intrathecal administration of UK from the cisterna magna may be a safe and reasonable means of preventing vasospasms and may result in improved treatment outcomes.

Crystallographic study of intein homing endonuclease II encoded in the archaeal DNA polymerase gene

Intein homing endonucleases are proteins spliced out from a precursor protein and site-specific enzymes that make double-strand breaks in inteinless alleles. Crystals of intein homing endonuclease II from the hyperthermophilic archaeon Pyrococcus kodakaraensis strain KOD1 (PI-PkoII) have been grown at room temperature using ammonium sulfate as a precipitant. The diffraction pattern of the crystal extends to 3.0 A resolution at room temperature upon exposure to synchrotron X-rays at KEK-PF, Japan. The crystals have symmetry consistent with space group C222(1), with unit-cell parameters a = 107.6, b = 150.5, c = 146.8 A. A full set of X-ray diffraction data were collected to 3.0 A Bragg spacing from a native crystal with an overall R(merge) of 4.8% and a completeness of 96.6%.

[A case of mixed connective tissue disease with lupus-like manifestations of the central nervous system, successfully treated with cyclophosphamide combined with prednisolone]

A 29-year-old woman experienced Raynaud's phenomenon, swelling of her fingers, eruptions on her face, and muscle weakness in 1990. She was diagnosed as having mixed connective tissue disease (MCTD) and was treated with prednisolone (PSL) for 3 years. Most of her complaints disappeared after the treatment. In March 1997, she experienced fever, erythema, and lymphadenopathy. Although she was treated with PSL (20 mg/day) again, muscle weakness, mental disturbance, and recto-urinary disturbance appeared. When she was re-admitted to our hospital, increased levels of muscle-derived enzymes and positivity of anti-RNP antibody were found. High signal areas in her cerebrum were shown by magnetic resonance imaging, and slow and spike pattern was shown by electroencephalography. Hypoperfusion of the cerebral blood flow was suggested on single photon emission computed tomography. The number of mononuclear cells, amount of protein and level of interleukin-6 were found to be elevated in her cerebrospinal fluid (CSF). Her neurological manifestations were diagnosed as being due to MCTD, and showed characteristics similar to those of systemic lupus erythematosus. She was treated with PSL (60 mg/day) followed by steroid pulse therapy. Because the response to this treatment was partial, oral administration of cyclophosphamide (CPM) (100 mg/day) was added. Muscle weakness and neurological abnormalities as well as abnormal laboratory findings gradually improved over the following two months. We conclude that the treatment with CPM combined with PSL may be useful, when neurological manifestations of MCTD are serious and resistant to conventional therapy.

Histopathological study of venous aneurysms in patients with dural arteriovenous fistulas

OBJECT

Of all intracranial dural arteriovenous fistulas (DAVFs), those with cortical venous drainage associated with cortical venous ectasia or varices are predisposed to an aggressive course and produce progressive neurological symptoms or hemorrhages. The authors undertook a histological examination of venous aneurysms and arterialized veins in the proximity of these aneurysms that had been surgically removed in patients with DAVFs.

METHODS

Surgical specimens were obtained in eight patients. The excised venous aneurysms and the arterialized veins in their proximity were stained using hematoxylin and eosin, van Gieson's elastic, and Masson's trichrome stain. Immunostaining was also performed for alpha smooth-muscle actin, desmin, and factor VIII antigen. Five of the patients had presented with venous hypertension, and three had intracranial hemorrhages. The arterialized vein obtained in the proximity of the venous aneurysm exhibited local irregular intimal thickening; the internal elastic lamina (IEL) was grossly preserved. All venous aneurysms in patients with venous hypertension manifested medial thickening and local intimal thickening with loss of IEL; the thickness of the wall was relatively uniform. In contrast, the wall thickness of venous aneurysms in patients with hemorrhage was extremely irregular and there was no clear delineation between the media and the intima. In media with complete disappearance of IEL, there was scant muscle tissue.

CONCLUSIONS

Degenerative changes in venous aneurysms in patients with hemorrhage were much greater than in patients with venous hypertension, possibly because hemorrhages result from a more complicated interplay of anatomical, hemodynamic, and degenerative factors.

The utility of the microcrystalline cellulose sphere as a particulate embolic agent: an experimental study

BACKGROUND AND PURPOSE

Although various particulate materials have been developed as embolization agents, their biocompatibility remains unclear. We used an animal model to examine the possibility of using FDA-approved microcrystalline cellulose spheres (CELPHERE) as solid embolic material for the permanent occlusion of blood vessels.

METHODS

Angiographic and histologic studies in 12 canine renal arterial systems were conducted to evaluate the performance of CELPHERE beads at 1 hour, and at 4 and 12 weeks after embolization.

RESULTS

The CELPHERE beads traveled to vessels with diameters approximating their own. Larger vessels were occluded by aggregations of beads. There was no disruption of vessel walls and no evidence of perivascular hemorrhage or inflammatory changes.

CONCLUSION

Because CELPHERE beads are easy to handle, highly biocompatible, and have few adverse effects, they are suitable for intravascular applications.

[A patient with limb-girdle type myasthenia gravis and atopic dermatitis, both of which improved after thymectomy]

We herein report a patient with myasthenia gravis (MG) and atopic dermatitis (AD). Heretofore, there have been no reports of patients with MG and AD. Nine years ago, a 25-year-old man noted muscle weakness of upper and lower extremities on physical labor, and the muscle weakness was gradually exacerbated. Two years ago, he noted acute skin eczema with itching on his hands and feet. Neurological examination revealed mild left ptosis, facial muscle weakness and proximal muscle weakness of upper and lower extremities, but no diplopia, ophthalmoplegia or dysphagia. Although anti-nicotinic acetylcholine receptor antibody was negative, edrophonium test was positive and 54% waning in the thenar muscles was observed on Harvey-Masland test. Thus, he was diagnosed as limb-girdle type MG. IgE level in his serum elevated (1,818 U/ml). After thymectomy, the muscle weakness markedly improved as well as waning in the thenar muscles (11%). Simultaneously, AD markedly improved and serum IgE level was decreased (1,245 U/ml). Thus, MG and AD in this case may be derived from some common immunological aberrancy in the thymus.

Radiation-induced cerebrovasculopathy of the distal middle cerebral artery and distal posterior cerebral artery--case report

A 15-year-old girl underwent partial removal of a pituitary adenoma followed by local irradiation of the brain with a total of 70 Gy through two lateral opposing ports. Twenty years later, she experienced frequent transient ischemic attacks with left sensory disturbance. Cerebral angiography revealed stenoses of the right distal middle cerebral artery (MCA) and the right distal posterior cerebral artery without net-like vessels. There was a severe decrease of vasoreactivity in the right hemisphere. Right superficial temporal artery (STA)-MCA anastomosis was performed. Her neurological deficits were resolved and perfusion reserve capacity had markedly improved 6 months later. We recommend STA-MCA anastomosis in such cases.

Successful treatment of a neonate with vein of Galen aneurysmal malformation

We present a follow-up study on a 5-year-old boy who was born with vein of Galen aneurysmal malformation (VGAM) accompanied by extreme cardiovascular distress. He was successfully treated by the staged endovascular technique during the neonatal stage. Postoperative angiographic study confirmed complete occlusion of the VGAM and the establishment of normal brain perfusion. At 5 years of age, the child is growing normally without neurological deficits or developmental retardation. We suggest that the restoration of normal brain perfusion in neonates with VGAM can cause normal brain development.

Expression of neuron specific phosphatase, striatal enriched phosphatase (STEP) in reactive astrocytes after transient forebrain ischemia

We studied the distribution and change of striatal enriched phosphatase (STEP) in the gerbil hippocampus after transient forebrain ischemia. STEP was expressed in the perikarya and in neuronal processes; it was not detected in non-neuronal cells of control animals. After 5-min forebrain ischemia, STEP immunoreactivity (STEP-IR) was preserved for 2 days; it disappeared 4 and more days after ischemia with completion of delayed neuronal death (DND) in the CA1 subfield. Furthermore, only in the CA1 after ischemia, STEP was expressed in reactive astrocytes for 4 to 28 days, showing different patterns of glial fibrillary acidic protein (GFAP)-positive reactive astrocytes. After non-or less-than lethal ischemia, STEP expression in reactive astrocytes corresponded with the degree of neuronal degeneration. Immunoblot analysis of the CA1 subfield revealed the expression of three isoforms, STEP45, -56 and -61; their expression patterns changed with time after ischemia. These data suggest that neuronal STEP is preserved until cell degeneration after ischemia and that STEP is expressed in reactive astrocytes only after lethal ischemia, with different expression patterns for its isoforms. Of STEP45, -56 and -61, STEP61 was the most strongly expressed in the reactive astrocytes; both STEP45 and -61 were expressed in neurons and the expression of STEP56 was weak. STEP may play an important role not only in neurons but also in reactive astrocytes after ischemia, depending on neuronal degeneration.

Prognostic significance of tumor grade for renal cell carcinoma

BACKGROUND

The natural history and prognosis of renal cell carcinoma cannot be predicted. Based on the Japanese classification system, the value of nuclear grade were assessed as a possible prognostic factor for renal cell carcinomas.

METHODS

In this retrospective study of 116 patients with renal cell carcinoma, radical nephrectomy was performed. Survival rates were calculated using the Kaplan-Meier method and multivariate analysis was performed using Cox's proportional hazard model.

RESULTS

Distribution by stage and grade in the population of renal cell carcinomas was as follows: pT1 in 13 cases (11.3%), pT2 in 65 cases (56.5%), pT3 in 36 cases (31.3%) and pT4 in one case (0.9%) and grade 1, 28 (24.1%), grade 2, 69 (59.5%) and grade 3, 16 (13.8%). Three cases could not be determined because of pre-operative embolization of the renal cell carcinomas. Nuclear grade was correlated with stage (P=0.0002), the presence of perirenal fat involvement (P=0.003) and metastases (P=0.007). A significant difference in survival was found between grades 1 and 3 (P=0.0001) and grades 2 and 3 (P=0.0001), respectively. Survival was significantly correlated with sex (P=0.0125), tumor size (P=0.0001), the presence of lymph node metastasis (P=0.0001), renal vein involvement (P=0.0001), perirenal fat involvement (P=0.002) or distant metastasis (P=0.0001). The multivariate analysis showed that the occurrence of tumor grade (P=0.0006) or distant metastasis were independent prognostic values.

CONCLUSION

The observations lead us to conclude that the nuclear grade according to the Japanese classification system appears to be of reliable prognostic value for renal cell carcinomas.

Enantioselective Single-Crystal-to-Single-Crystal Photodimerization of Coumarin and Thiocoumarin in Inclusion Complexes with Chiral Host Compounds

An intermolecular enantioselective photoreaction by a single-crystal-to-single-crystal transformation has been carried out for the first time, as is evident from X-ray structure analysis and X-ray powder diffractometric studies. This reaction, the dimerization of the title compound to cyclobutane derivative 1 (X=O, S), provides a good example for studying the mechanism of topochemical reactions in the crystal.

Spectroscopic and electrochemical properties of two azurins (Az-iso1 and Az-iso2) from the obligate methylotroph Methylomonas sp. strain J and the structure of novel Az-iso2

Two azurin-type blue copper proteins, which are related to the electron-transfer processes involving methylamine/methanol oxidation, have been spectroscopically and electrochemically characterized. The obligate methylotroph Methylomonas sp. strain J gives rise to two azurins (Az-isol and Az-iso2) with methylamine dehydrogenase (MADH-Mj). The intense blue bands characteristic of Az-iso1 and Az-iso2 are observed at 621 and 616 nm in the visible absorption spectra respectively, being revealed at 620-630 nm in those of usual azurins. The EPR signal of Az-iso1, similar to usual azurins, shows axial symmetry, while the axial EPR signal of Az-iso2 involves a slightly rhombic character. The half-wave potentials (E1/2) of the two azurins and the intermolecular electron-transfer rate constants (kET) from MADH-Mj to each azurin were determined by cyclic voltammetry. The E1/2 values of Az-iso1 and Az-iso2 are +321 and +278 mV vs NHE at pH 7.0, respectively. The kET value of Az-iso2 is larger than that of Az-iso1 by a factor of 5. However, the electron-transfer rate of Az-iso2 is interestingly slower than those of the azurins from a denitrifying bacterium, Alcaligenes xylosoxidans NCIB 11015, and the amicyanin from a different methylotroph, Methylobacterium extorquens AM1. The structure of Az-iso2 has been determined and refined against 1.6 A X-ray diffraction data. The whole structure of Az-iso2 is quite similar to those of azurins reported already. The Cu(II) site of Az-iso2 is a distorted trigonal bipyramidal geometry like those of other azurins, but some of the Cu-ligand distances and ligand-Cu-ligand bond angle parameters are slightly different. These findings suggest that Az-iso2 is a novel azurin and perhaps functions as an electron acceptor for MADH.

Crystallization and preliminary x-ray diffraction studies of C4-form phosphoenolpyruvate carboxylase from maize

Phosphoenolpyruvate carboxylase is a key enzyme in the fixation of atmospheric CO(2) in C(4) and crassulacean acid metabolism (CAM) plants. The enzyme catalyzes the irreversible carboxylation of phosphoenolpyruvate to form oxaloacetate and inorganic phosphate, the first committed step in the fixation of external CO(2) in these plants. The enzyme has been isolated from maize leaves and crystallized using the hanging-drop vapour-diffusion method with PEG 8000 as a precipitant at pH 7.5. The crystals belong to space group C222(1), with unit-cell dimensions a = 160.2, b = 175.6, c = 255.5 A, and diffract to 3.2 A resolution.

Structure comparison between oxidized and reduced plastocyanin from a fern, Dryopteris crassirhizoma

The X-ray crystal structures of oxidized and reduced plastocyanin obtained from the fern Dryopteris crassirhizoma have been determined at 1.7 and 1.8 A resolution, respectively. The fern plastocyanin is unique in the longer main chain composed of 102 amino acid residues and in the unusual pH dependence due to the pi-pi stacking interaction around the copper site [Kohzuma, T., et al. (1999) J. Biol. Chem. 274, 11817-11823]. Here we report the structural comparison between the fern plastocyanin and other plastocyanins from cyanobacteria, green algae, and other higher plants, together with the structural changes of fern plastocyanin upon reduction. Glu59 hydrogen bonds to the OH of Tyr83, which is thought to be a possible conduit for electrons, in the oxidized state. However, it moves away from Tyr83 upon reduction like poplar plastocyanin.

Hyperthermostable protein structure maintained by intra and inter-helix ion-pairs in archaeal O6-methylguanine-DNA methyltransferase

The crystal structure of O6-methylguanine-DNA methyltransferase (EC 2.1.1.63) of hyperthermophilic archaeon Pyrococcuskodakaraensis strain KOD1 (Pk -MGMT) was determined by single isomorphous replacement method with anomalous scattering (SIRAS) at 1.8 A resolution. The archaeal protein is extremely thermostable and repairs alkylated DNA by suicidal alkyl transfer from guanine O6 to its own cysteine residue. Archaea constitute the third primary kingdom of living organisms, sharing characteristics with procaryotic and eucaryotic cells. They live in various extreme environments and are thought to include the most ancient organisms on the earth. Structural studies on hyperthermophilic archaeal proteins reveal the structural features essential for stability under the extreme environments in which these organisms live, and will provide the structural basis required for stabilizing various mesophilic proteins for industrial applications. Here, we report the crystal structure of Pk-MGMT and structural comparison of Pk-MGMT and methyltransferase homologue from Escherichia coli (AdaC, C-terminal fragment of Ada protein). Analyses of solvent-accessible surface area (SASA) reveals a large discrepancy between Pk-MGMT and AdaC with respect to the property of the ASA. In the Pk-MGMT structure, the intra-helix ion-pairs contribute to reinforce stability of alpha-helices. The inter-helix ion-pairs exist in the interior of Pk-MGMT and stabilize internal packing of tertiary structure. Furthermore, structural features of helix cappings, intra and inter-helix ion-pairs are found around the active-site structure in Pk-MGMT.

Plausible phosphoenolpyruvate binding site revealed by 2.6 A structure of Mn2+-bound phosphoenolpyruvate carboxylase from Escherichia coli

We have determined the crystal structure of Mn2+-bound Escherichia coli phosphoenolpyruvate carboxylase (PEPC) using X-ray diffraction at 2.6 A resolution, and specified the location of enzyme-bound Mn2+, which is essential for catalytic activity. The electron density map reveals that Mn2+ is bound to the side chain oxygens of Glu-506 and Asp-543, and located at the top of the alpha/beta barrel in PEPC. The coordination sphere of Mn2+ observed in E. coli PEPC is similar to that of Mn2+ found in the pyruvate kinase structure. The model study of Mn2+-bound PEPC complexed with phosphoenolpyruvate (PEP) reveals that the side chains of Arg-396, Arg-581 and Arg-713 could interact with PEP.

Surgery and long-term outcome for ruptured anterior circulation aneurysms in patients in their ninth decade of life

BACKGROUND

The present pilot study was undertaken to analyze the long-term results of surgery for ruptured anterior circulation aneurysms in patients in their 9th decade of life.

METHODS

Between 1992 and 1997, we treated 10 consecutive patients with ruptured anterior circulation aneurysms who were 80 years or older on admission and judged eligible for surgery based on stringent criteria. The outcomes at discharge and the latest outcomes (obtained at a median of 41.6 months) were assessed using the Glasgow Outcome Scale and the Barthel Score, respectively.

RESULTS

Upon discharge, six of the 10 patients showed good recovery, two patients were moderately disabled, and two patients who suffered symptomatic vasospasm were severely disabled. As for the latest outcomes, assessed using Barthel Score, four patients had the maximum score of 100, two a score of 90, one a score of 35, two a score of 10, and one patient died. Of four patients who were in poor condition, two experienced deterioration attributable to unrelated causes 18 and 32 months after the ictus.

CONCLUSION

Advanced age alone does not preclude successful surgery for ruptured anterior circulation aneurysms. Carefully selected patients over 80 years should also be considered for surgical treatment.

Mitochondrial DNA replication in human T lymphocytes is regulated primarily at the H-strand termination site

The most unique feature in the replication of mitochondrial DNA (mtDNA) is that most of the newly synthesized heavy strands (H-strands) terminate prematurely, resulting in the formation of displacement loop (D-loop) strands. Only the H-strand which proceeds past the termination site is a true nascent H-strand leading to the overall replication on a circular mtDNA molecule. The physiological significance of the D-loop formation has long been unclear. To examine the role of premature termination in mtDNA replication, we therefore developed a method for selectively measuring both the total amount of nascent H-strands and the amount of true nascent H-strands using ligation-mediated polymerase chain reaction, which, for the first time, enabled us to estimate the frequency of premature termination. The stimulation of cell proliferation with interleukin 2 and phytohemagglutinin in human peripheral T lymphocytes caused an increase in the net replication rate of mtDNA. In stimulated cells, in comparison to resting ones, the amount of true nascent H-strands increased approx. 2.6-fold while the total amount of nascent H-strands remained unchanged, indicating that premature termination decreased while the initiation of replication remained the same. Our findings thus demonstrate the first clear example that premature termination plays a primary role in the up-regulation of the net rate of mtDNA replication in human cells.

Crystal structure determinations of oxidized and reduced pseudoazurins from Achromobacter cycloclastes. Concerted movement of copper site in redox forms with the rearrangement of hydrogen bond at a remote histidine

The crystal structures of oxidized and reduced pseudoazurins from a denitrifying bacterium, Achromobacter cycloclastes IAM1013, have been determined at 1.35- and 1.6-A resolutions, respectively. The copper site in the oxidized state exhibits a distorted tetrahedral structure like those of other pseudoazurins. However, not only a small change of the copper geometry, but concerted peptide bond flips are identified. The imidazole ring of remote His6 has a hydrogen bonding distance of 2.73 A between N-delta1(His6) and O-gamma1(Thr36) in the oxidized protein. When the protein is reduced at pH 6.0, the imidazole ring rotates by 30.3 degrees and moves 1.00 A away from the position of the oxidized state. A new hydrogen bond between N-epsilon2(His6) and O-epsilon1(Glu4) is formed with a distance of 3.03 A, while the hydrogen bond between N-delta1(His6)-O-gamma1(Thr36) is maintained with an interatomic distance of 2.81 A. A concomitant peptide bond flip of main chain between Ile34 and Thr36 occurs.