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J R Potts

Publications and source records attributed to J R Potts.

At least 19 recordsLinked to original sources
PubMed1998

Solution structure of the glycosylated second type 2 module of fibronectin.

Fibronectin is an extracellular matrix glycoprotein that plays a role in a number of physiological processes involving cell adhesion and migration. The modules of the fibronectin monomer are organized into proteolytically resistant domains that in isolation retain their affinity for various ligands. The tertiary structure of the glycosylated second type 2 module (2F2) from the gelatin-binding domain of fibronectin was determined by two-dimensional nuclear magnetic resonance spectroscopy and simulated annealing. The structure is well defined with an overall fold typical of F2 modules, showing two double-stranded antiparallel beta-sheets and a partially solvent-exposed hydrophobic cluster. An N-terminal beta-sheet, that was not present in previously determined F2 module structures, may be important for defining the relative orientation of adjacent F2 modules in fibronectin. This is the first three-dimensional structure of a glycosylated module of fibronectin, and provides insight into the possible role of the glycosylation in protein stability, protease resistance and modulation of collagen binding. Based on the structures of the isolated modules, models for the 1F22F2 pair were generated by randomly changing the orientation of the linker peptide between the modules. The models suggest that the two putative collagen binding sites in the pair form discrete binding sites, rather than combining to form a single binding site.

Amino Acid Sequence↗
PubMed1997

Solution structure of a type 2 module from fibronectin: implications for the structure and function of the gelatin-binding domain.

BACKGROUND: Fibronectin is an extracellular matrix glycoprotein involved in cell adhesion and migration events in a range of important physiological processes. Aberrant adhesion of cells to the matrix may contribute to the breakdown of normal tissue function associated with various diseases. The adhesive properties of fibronectin may be mediated by its interaction with collagen, the most abundant extracellular matrix protein. The collagen-binding activity of fibronectin has been localized to a 42 kDa proteolytic fragment on the basis of this fragment's affinity for denatured collagen (gelatin). This gelatin-binding domain contains the only type 2 (F2) modules found in the protein. The F2 modules of the matrix metalloproteinases MMP2 and MMP9 are responsible for the affinity of these proteins for gelatin. Knowledge of the structure of fibronectin will provide insights into its interactions with other proteins, and will contribute to our understanding of the structure and function of the extracellular matrix, in both normal and disease-altered tissues. RESULTS: We have determined the solution structure of the first F2 (1F2) module from human fibronectin by two-dimensional NMR spectroscopy. The tertiary structure of the 1F2 module is similar to that of a shorter F2 module, PDC-109b, from the bovine seminal plasma protein PDC-109. The 1F2 module has two double-stranded antiparallel beta sheets oriented approximately perpendicular to each other, and enclosing a cluster of highly conserved aromatic residues, five of which form a solvent-exposed hydrophobic surface. The N-terminal extension in 1F2 brings the N and C termini of the module into close proximity. CONCLUSIONS: The close proximity of the N and C termini in 1F2 allows for interactions between non-contiguous modules in the gelatin-binding domain. Thus, instead of forming an extended, linear chain of modules, the domain may have a more compact, globular structure. A pocket in the module's solvent-exposed hydrophobic surface may bind nonpolar residues in the putative fibronectin-binding site of the extracellular matrix component type I collagen.

Amino Acid Sequence↗
PubMed1996

Structure and function of fibronectin modules.

Fibronectin is an important component of the extracellular matrix and is involved in a diverse range of physiological processes. It is a mosaic protein composed almost entirely of three types of module, F1, F2 and F3. Although the structures of single F1, F2 and F3 modules have been available for a number of years, in many cases the key to understanding the structure-function relationships in fibronectin and other proteins containing these modules lies in studies of module pairs and larger domains. This review focuses on recent advances in the understanding of the structure and function of fibronectin modules.

Amino Acid Sequence↗
PubMed1996

Omental transposition in chronic spinal cord injury.

The results of omental transposition in chronic spinal cord injury have been reported in 160 patients operated upon in the United States, Great Britain, China, Japan, India and Mexico, with detailed outcomes reported in few studies. Recovery of function to a greater degree than expected by natural history has been reported. In this series, 15 patients with chronic traumatic spinal cord injury (> 1.5 years from injury) underwent transposition of pedicled omentum to the area of the spinal cord injury. Of the first series of four patients who were operated upon in 1988, one died, one was lost to follow-up and two were followed with sequential neurological examinations and Magnetic Resonance Imaging (MRI) scans preoperatively, at 1 year post injury and 4 1/2 years post injury. Another 11 patients were operated in 1992 and underwent detailed neurological and neurophysiological examinations and had MRI scans preoperatively and every 4 months for at least 1 year after surgery. All patients completed a detailed self-report form. Of the total of 13 operated patients in both series followed for 1-4 1/2 years, six reported some enhanced function at 1 year and five of these felt the changes justified surgery primarily because of improved truncal control and decreased spasticity. MRI scans showed enlargement of the spinal cord as compared to preoperative scans in seven patients. Increased T2 signal intensity of the spinal cord was found by 1 year after surgery in eight of 13 operated patients. Neurophysiological examinations of 11 patients in the second series agreed with self-reports of increases or decreases in spasticity (r = 0.65, P < 0.03). Somatosensory evoked potentials and motor evoked potentials at 4 month intervals up to 1 year in these patients showed no change after surgery. Neurological testing, using the American Spinal Injury Association (ASIA) and International Medical Society of Paraplegia (IMSOP) international scoring standards, failed to show any significant changes when the 1-year post operative examination was compared to the first preoperative examination except for decreased sensory function after surgery which approached statistical significance. When the 11 patients in the second series were compared to eight non-operated matched patients, followed for a similar length of time, no significant differences were found. Complications encountered in the operated patients from both series included one postoperative death from a pulmonary embolus, one postoperative pneumonia, three chronic subcutaneous cerebrospinal fluid (CSF) fistulae requiring wound revision, and one patient who developed biceps and wrist extensor weakness bilaterally requiring graft removal. We conclude that the omental graft remains viable over time and this operation can induce anatomical changes in the spinal cord as judged by MRI. Some patients reported subjective improvement but this was not supported by objective testing. We, therefore, find no justification for further clinical trials of this procedure in patients who have complete or sensory incomplete lesions. Further testing in motor incomplete patients would seem appropriate only with compelling supportive data.

Adolescent↗
PubMed1996

Anion channel blockers inhibit swelling-activated anion, cation, and nonelectrolyte transport in HeLa cells.

The effect of osmotic cell swelling on the permeability of HeLa cells to a range of structurally unrelated solutes including taurine, sorbitol, thymidine, choline, and K+ (96Rb+) was investigated. For each solute tested, reduction in the osmolality of the medium from 300 to 200 mosmol/kgH2O caused a significant increase in the unidirectional influx rate. In each case, the osmotically activated transport component was nonsaturable up to external substrate concentrations of 50 mM. Inhibitors of the swelling-activated anion channel of HeLa cells [quinine, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, niflumate, 1,9-dideoxyforskolin, 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB), and tamoxifen] blocked the osmotically activated influx of each of the different substrates tested, as well as the osmotically activated efflux of taurine and I-. Tamoxifen and NPPB were similarly effective at blocking the osmotically activated efflux of 96Rb+. The simplest of several hypotheses consistent with the data is that the osmotically activated transport of the different solutes tested here is via a swelling-activated anion-selective channel that has a significant cation permeability and a minimum pore diameter of 8-9 A.

Anions↗
PubMed1994

Fibronectin structure and assembly.

Significant progress has been made recently in the determination of the structure and assembly of the important matrix protein fibronectin, a molecule mainly constructed from three modular units denoted Fn1, Fn2 and Fn3. Atomic resolution structures are now available for all three single modules, for Fn1 and Fn3 module pairs, and for the disulphide-linked join between fibronectin monomers. Combined with results from new binding and mutation studies, the new structural information is leading to a clearer view of structure/function relationships in intact fibronectin.

Animals↗
PubMed1992

Anomeric preference of fluoroglucose exchange across human red-cell membranes. 19F-n.m.r. studies.

The rates of exchange across the human red-cell membrane of the alpha- and beta-anomers of the glucose derivative 3-fluoro-3-deoxy-D-glucose (3FG) were measured, under equilibrium-exchange conditions, using a 19F-n.m.r.-magnetization-exchange procedure. In experiments carried out over a range of 3FG concentrations (3.4-113 mM), the alpha-anomer was found to be transported with a smaller Km (greater apparent affinity) than the beta-anomer. In two experiments carried out at 34 and 37 degrees C the ratio (alpha/beta) of the Michaelis constants for exchange was 0.75 +/- 0.07 and 0.83 +/- 0.07 respectively and the Vmax for 3FG exchange was 28 +/- 3 and 33 +/- 3 mmol.s-1.litre of cells-1 respectively. In several experiments carried out at a single 3FG concentration (17 mM) and at 37 degrees C, using red cells from four individuals, the rate of exchange of the alpha-anomer across the membrane was significantly higher than that of the beta-anomer. The weighted mean value of the above-mentioned ratio was 0.79 +/- 0.07 for the four donors.

Biological Transport↗
PubMed1992

Urea exchange across the human erythrocyte membrane measured using 13C NMR lineshape analysis.

The 13C NMR spectrum of 13C-urea in a suspension of human red cells of reduced mean cell volume was observed to contain partially resolved resonances arising from the intra- and extracellular populations of the compound. It was shown that at 25 degrees C and a magnetic field strength of 9.4 T, the rate of exchange of urea between the intra- and extracellular populations was such that the NMR lineshape was sensitive to a change in the rate of 13C-urea exchange, induced either by the addition of the urea transport inhibitor phloretin, or by the addition of 12C-urea. Total lineshape analysis of 13C NMR spectra of 13C-urea in red cell suspensions containing different concentrations of 12C-urea resulted in a weighted mean estimate for the Km and Vmax for urea equilibrium exchange from three experiments of 44 +/- 18 mM and 3.1 +/- 0.6 x 10(-8) mol cm-2 s-1, respectively (the errors denote the weighted mean standard deviations). These estimates of Km and Vmax were significantly lower than previous values reported in the literature and determined using other techniques.

Adult↗
PubMed1991

The phenomenon of separate intra- and extracellular resonances of difluorophosphate in 31P and 19F NMR spectra of erythrocytes.

Trifluoroacetate and trifluoroacetamide, when added to a suspension of human red blood cells, give rise to separate 19F NMR signals from the intra- and extracellular species. This phenomenon has recently been exploited for measuring the membrane potential of erythrocytes. However, the separation of the peaks was incorrectly ascribed to a difference in magnetic susceptibility between the intra- and extracellular environments. Previously, we have reported well-resolved resonances in 31P NMR spectra for the intra- and extracellular populations of some phosphoryl compounds; in these cases, however, the intracellular peak is shifted to low frequency which is the opposite to the situation with the fluorinated compounds. By using difluorophosphate, which rapidly equilibrates across the membrane of human erythrocytes and which has both the phosphoryl and fluorine functional groups, we observed the separate intra- and extracellular resonances. But, the intracellular resonance was shifted to high frequency of the extracellular resonance in the 19F spectra and to low frequency in the 31P spectra. The basis for the phenomenon in both cases is thought to be the reduced hydrogen bonding inside the cells between the solvent water and the phosphoryl oxygen or fluorine atoms.

Erythrocytes↗
PubMed1991

Indications for gastric bypass in palliative operations for pancreatic carcinoma.

This review was undertaken to determine whether there are specific factors which predict the development of gastric outlet obstruction (GOO) in patients with pancreatic carcinoma. One hundred forty-two patients with biopsy proven pancreatic carcinoma had palliative operations of whom 74 had gastric bypass (GB). Of the 68 who did not, four died after biliary bypass. The 64 patients who remained at risk for GOO are the subject of this report. Seven of those patients developed GOO in the postoperative period and were compared with the 57 who did not. No significant difference was found between the two groups when they were compared on the basis of 20 historic, laboratory, and operative finding criteria. These data indicate that accurate prediction of subsequent GOO is not possible based on available objective data. Because GB creation does not increase operative blood loss, operative time, postoperative stay, or postoperative morbidity, and because prediction of need is difficult, prophylactic GB should be applied very liberally.

Adenocarcinoma↗
PubMed1991

Pancreatic-portal vein fistula with disseminated fat necrosis treated by pancreaticoduodenectomy.

I have reported the case of a 62-year-old man with chronic alcoholic pancreatitis and a rare pseudocyst-portal vein fistula. Even though he experienced no abdominal symptoms, he had severe metastatic fat necrosis manifested as subcutaneous fat necrosis, polyarthritis, medullary bone necrosis, and mental status changes. Remote tissue destruction continued until relief was gained by pancreaticoduodenectomy and repair of the necrotic portal vein. Disseminated fat necrosis is a rare syndrome that can be the only presenting feature in patients with pancreatitis and pancreatic cancer. Early recognition and treatment of the underlying pancreatic disease may decrease the high morality rate associated with this syndrome.

Adult↗
PubMed1990

Exchange of fluorinated glucose across the red-cell membrane measured by 19F-n.m.r. magnetization transfer.

The 19F n.m.r. spectrum of 3-fluoro-3-deoxy-D-glucose (3FG) in a red-cell suspension was observed to contain separate resonances from the intra- and extra-cellular populations of both the alpha- and beta-anomers. This phenomenon was used with an n.m.r. spin-transfer procedure to measure the rate of exchange of the anomers across the human red-cell membrane under equilibrium-exchange conditions at 37 degrees C. The beta-anomer crossed the membrane significantly more quickly than the alpha-anomer. At a total 3FG concentration of 9.3 mM; the first-order rate constants for the efflux of the alpha- and beta-anomers were 0.41 +/- 0.15 and 0.88 +/- 0.20 s-1 respectively. The measurable 3FG exchange was inhibited by 75 and 100% respectively by the glucose-transport inhibitors cytochalasin B and phloretin. Glucose inhibited the exchange of 3FG, and the results were consistent with glucose and 3FG binding to the hexose-transport protein with similar affinity.

Deoxy Sugars↗
PubMed1990

Palliative operations for pancreatic carcinoma.

Controversies in palliation of pancreatic carcinoma include the best biliary bypass, the best gastric by-pass, and how routinely gastric bypass should be used. We reviewed the records of 142 patients who underwent palliative operations for pancreatic carcinoma at the Cleveland Clinic over a 5-year period. Direct choledochal-enteric anastomosis proved superior to cholecystojejunostomy because of the high incidence of postoperative biliary sepsis and obstruction with the latter. The lowest incidence of these complications was achieved with choledochoduodenostomy. Loop gastrojejunostomy and Roux-Y gastrojejunostomy resulted in similar complication rates and postoperative stays, but, because loop reconstruction was simpler, it was deemed superior. Blood loss, operative time, and hospital stay were similar in patients with loop gastrojejunostomy and patients with no gastric bypass. This finding, coupled with a 10% incidence of subsequent gastric outlet obstruction in those without gastric bypass, indicates that gastric bypass should be liberally applied in the palliation of pancreatic carcinoma.

Adenocarcinoma↗
PubMed1989

Characterization of the transport of the nonelectrolyte dimethyl methylphosphonate across the red cell membrane.

We have refined the method for measuring the equilibrium exchange of the neutral phosphoryl compound dimethyl methylphosphonate across the human red cell membrane using 31P NMR spectroscopy. Using this improved technique we measured a permeability coefficient of dimethyl methylphosphonate of 9.47 +/- 1.01 X 10(-5) cm s-1 at a concentration of 164 mM, at 25 degrees C. The transport at 25 degrees C was not saturable up to a concentration of 600 mM and was not inhibited by 4,4'-diisothiocyano-2,2'-disulfonic acid, p-chloromercuriphenyl sulfonic acid, copper ions or phloretin, or by thiourea or urea at 16 degrees C. The permeability was enhanced by butanol and phloretin.

Biological Transport↗
PubMed1989

Clearance of atrial natriuretic factor by lung, liver, and kidney in human subjects and the dog.

We determined human and canine plasma clearance of atrial natriuretic factor (ANF) by lung, liver, and kidney from arteriovenous differences in plasma ANF and measured organ plasma flow. Human subjects had lower plasma ANF concentrations in the pulmonary vein or the pulmonary capillary wedge position when compared with the pulmonary artery, and both sites yielded pulmonary ANF extraction ratios of 24%. Canine lung ANF extraction was 19 +/- 3% and pulmonary ANF clearance was 328 +/- 78 ml/min per m2 vs. 357 +/- 53 ml/min per m2 in man. Hepatic plasma ANF clearance was 216 +/- 26 ml/min with an extraction ratio of 30 +/- 3% in humans and 199 +/- 89 ml/min and 36 +/- 6% in the dog. Renal plasma ANF clearance in human subjects was 78 +/- 12 ml/min per kidney and correlated well with each kidney's creatinine clearance (r = 0.58, P less than 0.05). The mean renal ANF extraction ratio was 35 +/- 4% in human subjects and 42 +/- 6% in the dog. These data quantitate the specific organ ANF clearances by lung, liver, and kidney in human subjects and in dogs and provide a rationale for elevated plasma ANF levels in cirrhosis, renal failure, and diseases accompanied by reduced perfusion of these organs. These findings support the conclusion that plasma ANF concentrations are dependent upon both the stimuli for ANF secretion as well as the specific organ clearances of ANF.

Adolescent↗