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Biomedical subjects

D C Richardson

Publications and source records attributed to D C Richardson.

At least 55 records · Page 3Linked to original sources
PubMed1990

De novo design, expression, and characterization of Felix: a four-helix bundle protein of native-like sequence.

The protein Felix was designed de novo to fold into an antiparallel four-helix bundle of specific topology. Its sequence of 79 amino acid residues is not homologous to any known protein sequence, but is "native-like" in that it is nonrepetitive and contains 19 of the 20 naturally occurring amino acids. Felix has been expressed from a synthetic gene cloned in Escherichia coli, and the protein has been purified to homogeneity. Physical characterization of the purified protein indicates that Felix (i) is monomeric in solution, (ii) is predominantly alpha-helical, (iii) contains a designed intramolecular disulfide bond linking the first and fourth helices, and (iv) buries its single tryptophan in an apolar environment and probably in close proximity with the disulfide bond. These physical properties rule out several alternative structures and indicate that Felix indeed folds into approximately the designed three-dimensional structure.

Amino Acid Sequence↗
PubMed1990

Radiotherapy prior to cortical allograft limb sparing in dogs with osteosarcoma: a dose response assay.

Twenty-one dogs with spontaneously occurring appendicular osteosarcoma were given preoperative radiation therapy prior to a limb sparing procedure using a cortical allograft. Radiation doses were randomly assigned, ranged from 36-52 Gy in 4 Gy intervals, and were given in 10 equally-sized fractions on a M, W, F schedule. Seventeen of the 21 dogs underwent the limb sparing procedure approximately 3 weeks after completion of radiation therapy. Local tumor recurrence was documented in 4 of 17 dogs at mean and median times of 5.5 and 5.8 months, respectively, after initiation of radiation therapy. Three of 4 recurrences were in anatomic regions with sparse adjacent soft tissue which precluded wide excision. Complications were significant. Fixation device failure occurred in 9 of 17 dogs and was associated with host bone necrosis, muscle thinning and fibrosis of vessels and nerves in irradiated normal tissue. Incidence of host bone necrosis was directly related to radiation dose (Kendall's statistic, p = 0.005). Metastasis occurred in all 21 dogs. Mean and median times to metastasis in these dogs were 5.1 and 4.0 months, respectively, after initiation of radiation therapy. Local tumor control rates and survival times were higher in dogs developing allograft infection suggesting that infection acted as an immunostimulant. All local failures occurred in dogs that did not develop allograft infection and median survival times for uninfected versus infected dogs were 5 and 11 months, respectively (logrank test, p = 0.029). Increased tumor radiopacity following radiation therapy was significantly related to survival. Median survival in dogs whose tumors were characterized by decreased, unchanged or increased opacity after radiation therapy were 3.5 and 14 months, respectively (logrank test, p = 0.014). Based on the results of our study, radiation therapy can not be recommended as part of limb sparing treatments for patients with osteosarcoma at doses and dose per fraction values similar to those used herein.

Animals↗
PubMed1989

Effect of Nd:YAG laser energy on articular cartilage healing in the dog.

The effect of low dose neodymium:yttrium aluminum garnet (Nd:YAG) laser therapy on cartilage healing was studied. Partial- and full-thickness cartilage defects were surgically created in the femoral condyles of 20 adult dogs. The cartilage defects in one limb of each dog were exposed to 30 J of Nd:YAG laser energy. The dogs were euthanatized 1 week (n = 6), 1 month (n = 7), and 6 months (n = 7) after surgery. Plastic-embedded, undecalcified histologic sections of each cartilage defect were examined for evidence of cartilage healing. Special stains were used to determine the type of repair tissue present, and morphometric measurements of repair tissue were made. No effect of Nd:YAG laser therapy on cartilage healing was noted.

Animals↗
PubMed1989

Urinary O6-methylguanine excretion in the rat after O6-methylguanine but not N-methylnitrosourea administration.

Urinary makers that permit monitoring the exposure of rats to methylating carcinogens could be of considerable value. Because of the association of the formation and retention of O6-methylguanine (m6Gua) with carcinogenesis, the urinary recovery of this compound would be of particular interest. Urine of rats receiving 200 muCi 3H-methyl nitrosourea (MNU) was therefore subjected to HPLC analysis to detect labeled m6Gua. Following the intraperitoneal injection of 3H-MNU (16 or 80 mg/kg), 3H-m6Gua could not be detected in the urine, although its presence was demonstrated in liver DNA under such conditions. Rats were also administered 3H-MNU followed by pretreatment with unlabeled m6Gua to block the repair enzyme, m6G-DNA-transmethylase, which might have obscured an excision mechanism. This procedure permitted the recovery of about half of the administered dose of m6Gua in the urine, but none of this compound contained tritium. We conclude that m6Gua, though formed in the DNA from MNU, is not excised and excreted as such in the urine. Thus m6Gua could not be used to serve as a suitable urinary marker for exposure to methylating carcinogens.

Animals↗
PubMed1988

Amino acid preferences for specific locations at the ends of alpha helices.

A definition based on alpha-carbon positions and a sample of 215 alpha helices from 45 different globular protein structures were used to tabulate amino acid preferences for 16 individual positions relative to the helix ends. The interface residue, which is half in and half out of the helix, is called the N-cap or C-cap, whichever is appropriate. The results confirm earlier observations, such as asymmetrical charge distributions in the first and last helical turn, but several new, sharp preferences are found as well. The most striking of these are a 3.5:1 preference for Asn at the N-cap position, and a preference of 2.6:1 for Pro at N-cap + 1. The C-cap position is overwhelmingly dominated by Gly, which ends 34 percent of the helices. Hydrophobic residues peak at positions N-cap + 4 and C-cap - 4.

Amino Acid Sequence↗
PubMed1988

Atypical Menkes steely hair disease.

Menkes steely hair disease (MSHD) is a rare disorder which typically results in severe mental retardation and death in early childhood. A 21-month-old boy with an atypical milder form was presented by Procopis et al. [1981]. A second child with the atypical form is presented here who has survived to age 9 years and is doing well clinically.

Brain Diseases, Metabolic↗
PubMed1988

Helix lap-joints as ion-binding sites: DNA-binding motifs and Ca-binding "EF hands" are related by charge and sequence reversal.

The DNA-binding helix pairs in gene repressor and activator proteins were compared with other approximately perpendicular pairs of adjacent helices in the known protein structures. Two other examples of closely matching conformations were found in cytochrome c peroxidase (residues 153-174) and in ribosomal L7/L12 protein (residues 68-89). Another group of such offset "lap-joints" are the Ca-binding "EF hand" structures, which bind a positive rather than a negative ligand. The EF hands turn out to match the DNA-binding motifs quite well (outside of the loop) if their sequence direction is reversed. This conformation is thus not as unusual as had been thought, but may have a more generalized role in ion binding and occasionally occur in a purely structural role.

Amino Acid Sequence↗
PubMed1986

The heme and Fe4S4 cluster in the crystallographic structure of Escherichia coli sulfite reductase.

Isolated hemoprotein subunits of Escherichia coli NADPH:sulfite reductase catalyze the 6-electron reduction of SO2-3 to S2-. The prosthetic groups of the hemoprotein, a siroheme and a Fe4S4 cluster, have been shown by spectroscopy to be tightly coupled. We have crystallized the isolated hemoprotein subunits and produced a 3-A electron density map by x-ray crystallography. A single heavy atom derivative and the native anomalous scattering (from the protein's 5 Fe and several S) were used to calculate the phases. In the electron density map, the cluster has a geometry similar to other Fe4S4 clusters. Both the cluster and the siroheme are found near the surface of the protein. The siroheme and the Fe4S4 cluster pack next to each other in the structure, apparently with a common ligand, consistent with a cysteine S gamma, shared by the siroheme Fe and one of the cluster Fe. The distance from the siroheme Fe to the center of the cluster is 5.5 A and the distance from the siroheme Fe to the nearest cluster Fe is 4.4 A. The edge of the siroheme macrocycle appears to be in Van der Waals contact with a cubane S atom of the cluster. The sixth coordination position of the siroheme Fe appears unoccupied and is quite exposed to the solvent. Some possible implications of the proposed structure on the role of the bridged siroheme-Fe4S4 cluster in catalysis are discussed.

Chemical Phenomena↗
PubMed1984

Development of a mathematical model for predicting concentrations of small asbestos fibers.

The standard method of asbestos sample analysis by phase-contrast microscopy excludes fibers which are below the resolution limits of the light microscope. Electron microscopic studies revealed that fibers in these small size ranges comprise the majority of fibers in asbestos dust. This research was conducted to determine if the development of a mathematical model for predicting concentrations of small fibers (less than 5 microns length) based on phase-contrast concentrations was feasible. The model presented in this paper was evaluated for its practical utility and was determined to be of minimal value; however, it was felt that the development of a reasonably accurate model can be arrived at through continued research.

Asbestos↗
PubMed1984

Inhibition of arabinose 5-phosphate isomerase. An approach to the inhibition of bacterial lipopolysaccharide biosynthesis.

Arabinose 5-phosphate ( A5P ) isomerase is a key enzyme in the biosynthesis of lipopolysaccharide, an essential component of the outer membrane of Gram-negative bacteria. The mechanism of the isomerase is envisioned to involve an enediol intermediate. A series of compounds, which are analogues of the substrates or intermediate, were tested as inhibitors of A5P isomerase with the belief that a good inhibitor would stop bacterial growth or render the cells more susceptible to other antibiotics or natural defenses. In a series of phosphorylated sugars, the order of isomerase inhibitory activity was as follows: aldonic acids greater than alditols greater than aldoses. Nonphosphorylated sugars were much less inhibitory. The best inhibitor was erythronic acid 4-phosphate (54), which had Km/Ki = 29. None of the compounds displayed antibacterial activity in vitro.

Aldose-Ketose Isomerases↗
PubMed1983

Anaerobic bacteria associated with osteomyelitis in domestic animals.

Specimens of bony tissue or adjacent soft tissue from 19 animals with osteomyelitis were cultured aerobically and anaerobically. Fourteen specimens (74%) yielded anaerobic bacteria in pure culture or mixed with aerobic or facultative anaerobic bacteria. The most predominant genus encountered was an obligate anaerobe, Bacteroides. The most frequently isolated Bacteroides species was Bacteroides asaccharolyticus, which was isolated 5 times. The most frequently isolated anaerobe was Peptostreptococcus anaerobius, which was isolated 6 times. Staphylococcus aureus and Escherichia coli were the most frequently isolated aerobic bacteria, with 7 and 6 isolates, respectively.

Animals↗