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J Popham

Publications and source records attributed to J Popham.

7 recordsLinked to original sources
PubMed2002

Structural studies of biomaterials using double-quantum solid-state NMR spectroscopy.

Proteins directly control the nucleation and growth of biominerals, but the details of molecular recognition at the protein-biomineral interface remain poorly understood. The elucidation of recognition mechanisms at this interface may provide design principles for advanced materials development in medical and ceramic composites technologies. Here, we describe both the theory and practice of double-quantum solid-state NMR (ssNMR) structure-determination techniques, as they are used to determine the secondary structures of surface-adsorbed peptides and proteins. In particular, we have used ssNMR dipolar techniques to provide the first high-resolution structural and dynamic characterization of a hydrated biomineralization protein, salivary statherin, adsorbed to its biologically relevant hydroxyapatite (HAP) surface. Here, we also review NMR data on peptides designed to adsorb from aqueous solutions onto highly porous hydrophobic surfaces with specific helical secondary structures. The adsorption or covalent attachment of biological macromolecules onto polymer materials to improve their biocompatibility has been pursued using a variety of approaches, but key to understanding their efficacy is the verification of the structure and dynamics of the immobilized biomolecules using double-quantum ssNMR spectroscopy.

Amino Acid Sequence↗
PubMed2001

Expression, purification, and biophysical characterization of the BRCT domain of human DNA ligase IIIalpha.

The C-terminal regions of several DNA repair and cell cycle checkpoint proteins are homologous to the breast-cancer-associated BRCA-1 protein C-terminal region. These regions, known as BRCT domains, have been found to mediate important protein-protein interactions. We produced the BRCT domain of DNA ligase IIIalpha (L3[86]) for biophysical and structural characterization. A glutathione S-transferase (GST) fusion with the L3[86] domain (residues 837-922 of ligase IIIalpha) was expressed in Escherichia coli and purified by glutathione affinity chromatography. The GST fusion protein was removed by thrombin digestion and further purification steps. Using this method, (15)N-labeled and (13)C/(15)N-double-labeled L3[86] proteins were prepared to enable a full determination of structure and dynamics using heteronuclear NMR spectroscopy. To obtain evidence of binding activity to the distal BRCT of the repair protein XRCC1 (X1BRCTb), as well as to provide insight into the interaction between these two BRCT binding partners, the corresponding BRCT heterocomplexes were also prepared and studied. Changes in the secondary structures (amount of helix and sheet components) of the two constituents were not observed upon complex formation. However, the melting temperature of the complex was significantly higher relative to the values obtained for the L3[86] or X1BRCTb proteins alone. This increased thermostability imparted by the interaction between the two BRCT domains may explain why cells require XRCC1 to maintain ligase IIIalpha activity.

Amino Acid Sequence↗
PubMed2001

Tautomeric energetics of xanthine oxidase substrates: xanthine, 2-oxo-6-methylpurine, and lumazine.

The stability of the tautomers of each of the three important substrates of xanthine oxidase, xanthine, 2-oxo-6-methylpurine, and lumazine, was examined by quantum mechanical calculations. The geometries of these tautomers were optimized at the AM1, Hartree-Fock (HF/6-31G), and hybrid Hartree-Fock/density functional theory (B3LYP/6-31G(d)) levels of theory. The single point energies of some of the more stable tautomers for each of the substrates were calculated at the B3LYP/6-311 +G(2d,p) level of theory. The Conductor Polarized Continuum Model (CPCM) was used to evaluate the solvent effects on the relative stabilities of these tautomers. The calculations clearly identify the lowest energy tautomeric form for xanthine and lumazine. On the other hand, there appear to be three tautomers for 2-oxo-6-methylpurine, with only minor energetic differences in vacuo. In water, however, only one of them predominates. The lowest energy tautomers presumably represent the predominant tautomeric forms at the molybdenum center of xanthine oxidase during catalysis. Implications of these computational results are discussed in the context of enzyme catalysis.

Catalysis↗
PubMed1998

Enhancement of the cosmetic and functional outcome of enucleation with the conical orbital implant.

OBJECTIVE: The authors evaluated a new design of a conical-shaped enucleation implant to help minimize the occurrence of superior sulcus defects and maximize motility of the prosthesis. The implant shape is a modification of a sphere. It has a posterior conical projection paralleling the orbital walls, a superior projection supporting the soft tissues of the upper eyelid sulcus, a flattened anterior surface, and channels for each rectus muscle. DESIGN: The study design was a consecutive case series from the Oculoplastics and Orbital Service of the Massachusetts Eye and Ear Infirmary. INTERVENTION/PARTICIPANTS: A total of 45 patients (average age, 40 years; range, 13-75 years) had placement of a conical implant (39 primary enucleations, 6 secondary implants) with a minimum of 1 year' follow-up (range, 12-36 months). All of the primary enucleations and two of the secondary procedures had the anterior portion of the implant covered with autologous fascia. Four of the secondary implants were covered with pseudocapsule harvested from the explanted primary implant. Prostheses were fit 6 to 10 weeks after surgery. MAIN OUTCOME MEASURES: Postoperative appearance of patients was assessed by qualitative appearance of the superior sulcus and prosthetic motility, and subjectively by patients' satisfaction. RESULTS: A total of 43 patients had minimal or no superior sulcus defect, whereas 2 patients had moderate defects. There were no severe sulcus defects. All patients were satisfied with their appearance and did not seek further surgery to correct any upper sulcus asymmetry. Prosthetic motility with small-angle ductions (<10 degrees) and saccades was good in all cases. There were two cases of conjunctival wound dehiscence. Both occurred within 4 weeks of surgery. One wound dehiscence was sutured, whereas the other healed spontaneously. There were no cases of implant extrusion, migration, or infection. CONCLUSION: The conical orbital implant provides appropriate reconstitution of orbital volume while minimizing superior sulcus defects with adequate prosthetic motility.

Adolescent↗
PubMed1991

Mucoepidermoid carcinoma of the lacrimal gland. Report of a case with oncocytic features arising in a patient with chronic dacryops.

A 62-year-old woman had recrudescence of growth of a lacrimal gland fossa cystic mass present for more than 40 years. Results of histopathologic examination of the excised specimen showed infiltrating nests of epidermoid and mucin-producing cells, consistent with a mucoepidermoid carcinoma. Also present were numerous large oncocytic cells partially lining the lumens of the multiloculated cyst and penetrating the adjacent stroma. To the authors' knowledge, this is the first reported case of mucoepidermoid carcinoma with prominent oncocytic features arising in a previously documented chronic cystic lesion of the lacrimal gland. Because of the population of oncocytes (a metaplastic phenomenon encountered in ductular epithelial cells) among the cells lining the cyst, the authors conclude that the carcinoma arose from a long-standing dacryops. This conclusion was also supported by the electron microscopic demonstration of duct-type secretory granules within the mitochondria-rich oncocytes.

Carcinoma↗
PubMed1988

Angiographic cystoid macular edema after posterior chamber lens implantation.

We performed a prospective study evaluating the incidence of angiographic cystoid macular edema (CME) following extracapsular cataract extraction and posterior chamber intraocular lens implantation. Of the 162 eyes in the study, 141 were randomized into either a primary capsulotomy or a capsule intact group. The remaining eyes were not randomized due to intraoperative surgical complications, but they were included in the follow-up studies. Six weeks after surgery, angiographic CME was documented in 24% of the capsulotomy group and in 16% of the capsule intact group. The differences were not statistically significant. Including nonrandomized cases reduced the overall incidence of angiographic CME and the difference between the two groups. Angiographic CME was usually not extensive, and it was associated with a visual acuity less than 20/40 in 2.5% of eyes six weeks postoperatively. A subgroup of 120 eyes was followed up for approximately six months, when angiographic CME was present in 4% of the capsulotomy and capsule intact groups.

Aged↗