Crystal structure of glutathione synthetase at optimal pH: domain architecture and structural similarity with other proteins

The crystal structure of Escherichia coli B glutathione synthetase (GSHase) has been determined at the optimal catalytic condition pH 7.5. The most significant structural difference from the structure at pH 6.0 is the movement of the central domain towards the N-terminal domain almost as a rigid body. As a result of this movement, new interdomain and intersubunit polar interactions are formed which stabilize the dimeric structure further. The structure of GSHase at optimal pH was compared with 294 other known protein structures in terms of the spatial arrangements of secondary structural elements. Three enzymes (D-alanine: D-alanine ligase, succinyl-CoA synthetase and the biotin carboxylase subunit of acetyl-CoA carboxylase) were found to have structures similar to the ATP-binding site of GSHase, which extends across two domains. The ATP-binding sites in these four enzymes are composed of two antiparallel beta-sheets and are different from the classic mononucleotide-binding fold. Except for these proteins, no significant structural similarity was detected between GSHase and the other ATP-binding proteins. A structural motif in the N-terminal domain of GSHase has been found to be similar to the NAD-binding fold. This structural motif is shared by a number of other proteins that bind various negatively charged molecules.

[MR imaging of hepatocellular carcinoma following microwave coagulation therapy]

MRI was performed in 13 patients who had microwave coagulation therapy (MCT) for hepatocellular carcinoma. Six of them underwent surgery after MRI. The area (including tumor) treated by MCT showed low to high intensity on T1WI, and low to isointensity on T2WI. No enhancement was obtained on dynamic MRI. Histologically, this area was supposed to be coagulation necrosis. On T1WI, only tumor showed high intensity within the MCT area in 8 patients, and nearly uniform intensity was observed in 5 patients. Histologically, residual cell nuclei were observed in the former, and nearly uniform coagulation necrosis in the latter. The marginal part of the MCT area exhibited low intensity on T1WI, and high intensity on T2WI. Strong enhancement was obtained on dynamic MRI, and histologically, granulation tissue was noted. In the hepatic parenchyma around the MCT area, a ring-or wedge-shaped high intensity part was observed in 7 patients on T2WI, and that part was enhanced on dynamic MRI. This finding was considered to reflect changes such as hepatic hyperperfusion. In terms of the capability of visualizing residual tumor after MCT, MRI was superior to CT. Furthermore, a clear distinction was seen between the MCT area and non-MCT area on T2WI and dynamic MRI. Thus, MRI was useful in the determination of additional therapy.

Gadolinium-enhanced MR imaging of the wrist in rheumatoid arthritis: value of fat suppression pulse sequences

OBJECTIVE

To determine the usefulness of fat-suppressed gadolinium (Gd)-enhanced MR imaging of the wrist in patients with rheumatoid arthritis (RA).

DESIGN AND PATIENTS

Fat-suppressed Gd-enhanced T1-weighted spin-echo (SE) images were obtained and compared with other standard techniques in 38 wrists of 27 patients (22-77 years) with RA. Scoring based on the degree of synovial enhancement of each joint was developed and the total scores (J-score) were correlated with radiographic stage, C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and symptomatic change in the follow-up study.

RESULTS

Synovial proliferations showed marked enhancement in all the wrists. In addition, contrast enhancement in the bone marrow and tenosynovium was seen in 36 and eight wrists respectively. Fat-suppressed Gd-enhanced T1-weighted images demonstrated these abnormalities better than other techniques. The J-scores correlated well with values of CRP (P = 0.0034), but not with radiographic stages and ESR.

CONCLUSION

Fat-suppressed Gd-enhanced T1-weighted SE images can clearly demonstrate most of the essential lesions in RA including the proliferative synovium, bone erosion, bone marrow inflammatory change, and tenosynovitis. Scoring based on the extent of Gd-enhancement of synovium can be useful in the assessment of the inflammatory status.

A pseudo-michaelis quaternary complex in the reverse reaction of a ligase: structure of Escherichia coli B glutathione synthetase complexed with ADP, glutathione, and sulfate at 2.0 A resolution

The crystal structure of glutathione synthetase from Escherichia coli B complexed with ADP, glutathione, and sulfate has been determined at 2.0 A resolution. Concerning the chemical similarity of sulfate and phosphate, this quaternary complex structure represents a pseudo enzyme-substrate complex in the reverse reaction and consequently allows us to understand the active site architecture of the E. coli glutathione synthetase. Two Mg2+ ions are coordinated with oxygen atoms from the alpha- and beta-phosphate groups of ADP and from the sulfate ion. The flexible loops, invisible in the unliganded or the binary and ternary complex structures, are fixed in the quaternary complex. The larger flexible loop (Ile226-Arg241) includes one turn of a 310-helix that comprises the binding site of the glycine moiety of GSH. The small loop (Gly164-Gly167) is involved in nucleotide binding and acts as a phosphate gripper. The side chains of Arg210 and Arg225 interact with the sulfate ion and the beta-phosphate moiety of ADP. Arg 210 is likely to interact with the carboxylate of the C-terminal gamma-glutamylcysteine in the substrate-binding form of the forward reaction. Other positively charged residues in the active site (Lys125 and Lys160) are involved in nucleotide binding, directing the phosphate groups to the right position for catalysis. Functional aspects of the active site architecture in the substrate-binding form are discussed.

[Natural history of cloudy zone of pulmonary adenocarcinoma on HRCT]

Seven pulmonary adenocarcinomas with cloudy zone (CZ), which was defined as a lower density zone in the pulmonary lesion than pulmonary vessels in the surrounding normal lung on high resolution computed tomography (HRCT), were followed up for at least 3 months. There were three tumors with homogeneous CZ, one of which showed no change when rescanned after three months, the others showed enlargement with or without replacement by high density areas on rescanned images obtained after more than one year. Two tumors containing some high density areas on the initial scans showed slight decreases in size on rescanned images obtained after 1 to 3 months. However, on rescanned images obtained after more than 1 year and 9 months, these tumors also showed enlargement of CZ. Pathologically, CZs corresponded to well-differentiated adenocarcinoma of the bronchioloalveolar type with no or mild interstitial change, whereas high density areas mainly corresponded to papillary adenocarcinoma with severe interstitial fibrosis. In conclusion, long-term careful follow-up of CZ is necessary to detect enlargement or the appearance of high density. Unchanged CZ in short-term follow-up should be considered a finding suggestive of malignancy.

Parathyroid hormone-related protein (PTHrP) action in rat articular chondrocytes: comparison of PTH(1-34), PTHrP(1-34), PTHrP(1-141), PTHrP(100-114) and antisense oligonucleotides against PTHrP

Parathyroid hormone-related protein (PTHrP) is thought to be an important autocrine/paracrine factor for chondrocyte metabolism since mice lacking the PTHrP gene exhibit abnormal cartilage development. To determine the biological role of PTHrP in chondrocytes, we first compared the agonist potency of human (h) PTHrP(1-34) with hPTH(1-34) in cultured rat articular chondrocytes. Neither hPTHrP(1-34) nor hPTH(1-34) altered basal DNA synthesis, but attenuated the stimulatory effect of transforming growth factor beta (TGF-beta). Both agents suppressed the expression of alpha(1) type II collagen mRNA in a dose-response fashion with the same potency. In addition, the action of exogenously added hPTHrP(1-34) and hPTH(1-34) on intracellular cAMP and [Ca2+]i levels was similar. We next compared the effect of PTHrP within its entire amino acid sequence (1-141). With regard to thymidine incorporation, alpha(1) type II collagen gene expression and accumulation of cAMP and [Ca2+]i level, there was no significant difference between hPTHrP(1-34) and hPTHrP(1-141). PTHrP C-terminal (100-114) did not show any function. To further investigate PTHrP function, intracellular PTHrP translation was inhibited by a transgene of antisense oligonucleotides against PTHrP. Antisense oligonucleotides decreased PTHrP mRNA translation, specifically inhibited DNA synthesis in control as well as TGF-beta-treated chondrocytes and enhanced alpha(1) type II collagen mRNA expression in TGF-beta-treated chondrocytes. These results suggest that there is no significant difference between exogenously added hPTH(1-34), hPTHrP(1-34) and PTHrP(1-141) with regard to the biological action of these agents, including cell growth, differentiation and second messenger pathway. However, the result of DNA synthesis in the antisense PTHrP-inhibition study suggests that intracellular PTHrP may have an as yet unknown biological role, in addition to a classical PTH/PTHrP receptor-mediated function in the rat articular chondrocyte.

Vascular occlusion and cartilage disorders in osteonecrosis of the femoral head in rats

The aim of our study was to clarify the role of lateral epiphyseal vessels in the development of femoral head osteonecrosis in rats. We did this by performing histological and immunological studies on rats at the age that they are most prone to spontaneous osteonecrosis. We observed that obstruction of the lateral epiphyseal vessels occurred at the site of cartilage penetration. This obstruction preceded the development of osteonecrosis in adjacent areas of the femoral head. We propose that a similar mechanism may be responsible, in part, for the development of Perthes disease in man.

Classification of air density areas in CT-pathologic correlation of pulmonary adenocarcinoma

Air density areas (ADAs) such as air bronchogram, bubble-like area, and cavity on high resolution computed tomography (HRCT) of pulmonary adenocarcinoma were examined to clarify their pathological implications. Forty-two resected specimens of pulmonary adenocarcinoma were histopathologically examined in correlation with the HRCT findings with particular emphasis on ADAs. Forty-one ADAs observed in 32 of 42 cases with pulmonary adenocarcinoma were classified into three types: air bronchogram type (n = 22), bubble-like area type (n = 12), and cavity type (n = 8). Twenty of 22 air bronchogram ADAs corresponded to bronchi. Nine of 12 bubble-like area ADAs corresponded to bronchioles. Only one of eight cavity-ADAs consisted of necrosis. The classification of ADAs in pulmonary adenocarcinoma is considered to be useful in interpreting HRCT findings of pulmonary nodules.

Searching for common sequence patterns among distantly related proteins

We have developed a program Gap Allowing Pattern Explorer (GAPE) to extract amino acid sequence motifs conserved among distantly related proteins. The GAPE program is designed to allow gaps in the sequences. First, this program generates all possible amino acid patterns comprising up to five amino acids. Sequences containing the amino acid residues in the same order as a generated pattern are selected as subsequences, where the differences in the distances between two consecutive amino acids are ignored. Next, the motifs are extracted from the subsequences under conditions in which all four distances between the five amino acids are fixed. At this stage, motifs with gaps in their subsequence are also found by relaxing one of the four fixed distances. The statistical significance for a motif obtained is calculated based on the amino acid composition of the sequences under consideration. When the GAPE program was applied to 59 pyridoxal-phosphate-related sequences and 64 ATP (AMP-forming)-related sequences, motifs extracted with a low expectation of occurrence contained some of the amino acid residues chemically proved to be involved in the ligand recognition.

Cloudy nodule on HRCT: a new clinico-radiologic entity of pulmonary adenocarcinoma

We propose cloudy nodule (CN) on HRCT as a special type of pulmonary adenocarcinoma. CN was defined as a cloudy nodular shadow in the peripheral part of the lung with lower density than pulmonary vessels on HRCT. Radiologic images of nine CNs in eight cases were correlated with the pathological findings of the resected specimen. All CNs were clearly demarcated on HRCT. They were pathologically composed of well differentiated adenocarcinoma, mainly bronchioloalveolar type with little or no central scar. Plain films were negative in six of nine cases. CN on HRCT may indicate well-differentiated adenocarcinoma with good prognosis.

Site-directed mutagenesis of glutathione synthetase from Escherichia coli B: mapping of the gamma-L-glutamyl-L-cysteine-binding site

Lys18, Arg86, Asn283, Ser286, Thr288 and Glu292 of glutathione synthetase from Escherichia coli B are presumed to be highly concerned with the substrate, gamma-L-glutamyl-L-cysteine (gamma-Glu-Cys), binding by X-ray crystallography and affinity labeling studies. Using site-directed mutagenesis, we investigated functional roles of those residues for gamma-Glu-Cys binding. The mutant enzymes of Arg86 and Asn283 altered their kinetic parameters, especially the Michaelis constants of gamma-Glu-Cys. In the case of Asn283, the residue is not likely to have an essential role in gamma-Glu-Cys binding but its side chain would extend to make a van der Waals contact with bound gamma-Glu-Cys. Chemical modification of a cysteine residue with 5,5'-dithiobis(2-nitrobenzoate) (DTNB) showed Arg86 would not only be much responsible for gamma-Glu-Cys binding but would also have a role in maintaining the structural integrity of the enzyme. The other mutant enzymes showed little defect in their kinetic parameters of gamma-Glu-Cys.

[High-resolution CT findings of Pneumocystis carinii pneumonia]

High resolution CT (HRCT) was performed on 7 patients with pneumocystis carinii pneumonia (PCP). Six cases were proven bacteriologically by bronchoalveolar lavage; one case was proven by autopsy. Three patients were re-scanned after specific treatment and symptomatic relief. All the CT scans were abnormal, usually showing bilateral diffuse ground-glass opacity, through which the pulmonary vessels remained visible. Chest X-ray, on the other hand, showed a normal pattern in one patient. Other changes such as air space consolidation (in 4 cases) and thickening of peripheral pulmona vessels (in 2 cases) were also seen. Air space consolidation was found in three cases with mixed infection (cytomegalovirus pneumonia in 2 cases, aspergillosis in one case). No patient showed significant mediastinal or hilar lymph node enlargement, pleural effusion or cystic pulmonary change. HRCT findings such as ground-glass opacity and air space consolidation were shown to disappear in some cases of PCP after specific treatment. HRCT is useful to evaluate the sequential pulmonary changes after the specific therapy.

Concurrent radiotherapy and chemotherapy with protracted continuous infusion of 5-fluorouracil in inoperable esophageal squamous cell carcinoma

PURPOSE

The feasibility of a concurrent chemoradiotherapeutic protocol for patients with inoperable esophageal squamous cell carcinoma was tested.

METHODS AND MATERIALS

Concurrent chemoradiotherapy using protracted low-dose continuous infusions of five-fluorouracil (5-FU; 250-300 mg/m2/24 h) and standard external beam irradiation was given to 28 patients with inoperable esophageal squamous cell carcinoma between November 1991 and June 1993.

RESULTS

For 25 patients receiving a total dose of > or = 60 Gy and concurrent 5-FU infusion for more than 5 weeks, the complete response rate was 52%. Local progression-free rate in this chemoradiotherapy group was significantly higher than the historical controls treated by radiotherapy alone (p < 0.05). A multivariate analysis revealed the treatment scheme (concomitant chemoradiotherapy vs. radiotherapy alone) to be a significant factor in local control (p < 0.01). Swallowing pain (39%), anorexia (39%), and nausea (32%) were the most frequent early reactions. Serious late radiation complications have not been observed.

CONCLUSION

The concurrent chemoradiotherapy using protracted low-dose continuous infusion of 5-FU and standard radiotherapy is an effective and safe method to obtain a local control in inoperable esophageal squamous cell carcinoma.

[A case of mesenteric panniculitis: comparing the findings of 67Ga scintigraphy with pathological results]

We report a case of mesenteric panniculitis where we compared the findings of 67Ga-citrate (Ga) scintigraphy with pathological results. The patients, a 75-year-old man, was hospitalized for examination of low abdominal mass. After hospitalization he developed high CRP levels. A Ba enema revealed serrated intestinal walls and a thick fat density, the margins of which were distinct, as judged from abdominal CT scans. Therefore we suspected a mesenteric panniculitis. Since the patient did not improve under conservative treatment for three months, surgery was performed a day after Ga scintigraphy which showed the abnormal uptake in the abdominal mass, which was removed. The radioactivity of several tissue slices from the resected specimen containing the affected part which had been described inflammatory in the pathological examination showed very high radioactivity. This disease is usually diagnosed from the typical findings of Ba enema and CT scan. But, when an extraordinary abdominal accumulation presents, one should think of performing a Ga scan as an additional diagnostic parameter.

[Embolization of varicocele with ethanol]

Embolization with ethanol was performed in 40 varicocele patients to prevent recurrence due to collateral formation. A prescribed amount of ethanol (0.5-4 ml) was injected slowly into the testicular vein with the catheter tip as close as possible to the inguinal region. Embolization with stainless steel coils was also performed in 15 of the 40 patients. Immediately after embolization, three varicoceles were reduced in size, and 37 disappeared. Recurrence was recognized in only two patients. These patients were embolized at a proximal site above lumbar vertebra IV. Spermatic data have improved for 13 patients but not for one azoospermatic patient. Serious complications were recognized in only one patient, who received an injection of 15 ml ethanol in one dose. Therefore, we conclude that embolization with ethanol is an useful treatment for varicocele.

Characterization of a catalytic antibody for stereoselective ester hydrolysis--a catalytic residue and mode of product inhibition

A catalytic antibody which catalyzes stereoselective ester hydrolysis was characterized, and the role of a catalytic Arg residue is discussed in terms of product inhibition. A monoclonal antibody 1C7 generated against the phosphonate 1 was highly stereoselective for (R)-isomer in hydrolyzing racemic ester 2. However, the reaction was almost stoichiometric due to strong inhibition by the product acid 3. One Arg residue in the antibody combining site was essential to the catalysis, and the same Arg was expected to play a dominant role in product inhibition by charge interaction with the negatively charged product acid. Indeed, the antibody experienced much less product inhibition with the hydrolysis of a carbonate ester 7, which yields a neutral alcohol 8 devoid of a negative charge, and exhibited at least 100 turnovers without any loss of activity. In addition, high stereoselectivity for (R)-isomer was still retained. The amino acid sequence and computer modeling of the variable domain of 1C7 suggested that Arg97 in the complementarity-determining region (CDR) of heavy chain was the putative catalytic residue.

Flexible loop that is novel catalytic machinery in a ligase. Atomic structure and function of the loopless glutathione synthetase

The catalytic mechanism of glutathione synthetase is proposed to proceed via phosphorylation of the dipeptide substrate to yield an acyl phosphate intermediate; this intermediate is subsequently attacked by glycine, followed by loss of inorganic phosphate, leading to glutathione formation. A flexible loop (Ile226-Gly242) in Escherichia coli B glutathione synthetase is proposed to stabilize the acyl phosphate intermediate by preventing its decomposition by hydrolysis with water [Tanaka, T., Kato, H., Nishioka, T., & Oda, J. (1992) Biochemistry 31, 2259-2265; Tanaka, T., Yamaguchi, H., Kato, H., Nishioka, T., Katsube, Y., & Oda, J. (1993) Biochemistry 32, 12398-12404]. To investigate the function of the loop in the E. coli enzyme definitely, a loopless mutant in which the loop (Ile226-Arg241) was replaced with three residues of glycine was constructed. The crystal structure of the loopless mutant enzyme was essentially identical with that of the wild-type enzyme. Kinetic measurements showed that the replacement of the loop led to increases in the Km values, especially for the glycine, and a 930-fold decrease in the k0 value. Hence, the loopless mutant was 3 x 10(4) less active in terms of its specificity constant (k0/Km) for glycine than the wild-type enzyme. Moreover, the loopless mutant showed gamma-L-glutamyl-L-cysteine-dependent ATP hydrolase activity to almost the same extent as its glutathione synthetase activity. These studies support the fact that the loop enhances the recognition of glycine as well as stabilizes the acyl phosphate intermediate so that the intermediate rapidly reacts with glycine.

[Evaluation of renal function by factor analysis using 99mTc-MAG3]

The kinetics of 99mTc-mercapto-acetyltriglycine (MAG3), a new renal scintigraphic agent, was studied by factor analysis in patients with chronic renal disorders, and its application to assessment of the renal function was evaluated. Data were collected for 30 minutes from immediately after intravenous injection of MAG3 at 370 MBq, the first pass image and serial renal scintigrams were obtained, and factor analysis was attempted simultaneously. Since most of MAG3 is excreted via the kidney during the first pass, factor analysis was performed. Two factors reflecting renal parenchymal components and pelvic components could be separated in 8 (Cre < or = 2.9 mg/dl) of 10 patients, and they corresponded with respective segmental renograms. In the remaining 2 (Cre > or = 3.0 mg/dl), separation was impossible by 2-factor analysis, and 3-factor analysis was needed. Factor analysis is considered to allow objective evaluation of renal function without setting the ROI.

Flexibility impaired by mutations revealed the multifunctional roles of the loop in glutathione synthetase

The loop from Ile-226 to Arg-241 in the glutathione synthetase (GSHase) from Escherichia coli B is rich in glycine and alanine and too flexible to take a fixed conformation [Yamaguchi, H., Kato, H., Hata, Y., Nishioka, T., Kimura, A., Oda, J., & Katsube, Y. (1993) J. Mol. Biol. 229, 1083-1100; Tanaka, T., Kato, H., Nishioka, T., & Oda, J. (1992) Biochemistry 31, 2259-2265]. To restrict the flexibility, three residues in the loop, Pro-227, Gly-229, and Gly-240, were replaced with alanine and valine residues. Variability in conformations of the mutant loops and shifts in the distribution of conformers between the open and closed states were assessed by steady-state kinetics, X-ray crystallographic structure analysis, and proteolysis with arginyl endopeptidase. Mutant enzymes replaced with a valine residue at the basal positions of the loop (P227V, G240V, and P227V/G240V) were identical with the wild-type enzyme in their crystal structures, except the loop region. The mutant loops retained apparent conformational variability, so as to take the open and closed states and to protect the acyl phosphate intermediate from the decomposition uncoupled from glutathione synthesis, but lost the catalytic activity; Kmapp values for glycine and gamma-Glu-Cys were sensitive to the mutations and drastically increased, and the k0app value was fatally reduced in the P227V/G240V mutant enzyme. The present results suggest that adjustability of the loop to the closed state is required for the recognition of the substrates, gamma-Glu-Cys and glycine, and for the chemical interactions with the bound substrates.

Fibroma of tendon sheath with ulceration

We describe a 44-year-old man with fibroma of tendon sheath. The tumor originated in the foot and developed an ulcer during its course. It was totally excised, and the defect was reconstructed by full-thickness skin graft. The patient has been free of any recurrence during the follow-up period of one year. Fibroma of tendon sheath rarely occurs in the foot, and, to our best knowledge, this condition with ulceration is the first case reported.

SPECT imaging in a case of primary respiratory tract amyloidosis

SPECT findings in a very rare case of primary amyloidosis localized in the laryngotracheobronchial area are reported. SPECT using Tc-99m PYP revealed widespread uptake in the larynx and the entire tracheobronchial tree up to the subsegmental divisions; the areas corresponded to diffuse thickening and calcification of the walls on CT. SPECT using Ga-67 citrate also showed marked uptake in the same area, consistent with the findings shown by SPECT using Tc-99m PYP.