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M E Johnson

Publications and source records attributed to M E Johnson.

At least 145 records · Page 8Linked to original sources
PubMed1990

Secondary structure prediction for the spectrin 106-amino acid segment, and a proposed model for tertiary structure.

A collective secondary structure prediction for the human erythrocyte spectrin 106-residue repeat segment is developed, based on the sequences of nine segments that have been reported in the literature, utilizing a consensus of several secondary structure prediction methods for locating turn regions. The analysis predicts a five-fold structure, with three alpha-helices and two beta-strand regions, and differs from previous models on the lengths of the helices and the existence of beta-strand structure. We also demonstrate that this structural motif can be folded into tertiary structures that satisfy the experimental spectrin data and several general principles of protein organization.

Circular Dichroism↗
PubMed1989

QSAR and molecular shape analysis of aryl-substituted alanine analogs as antigelling agents.

Quantitative structure activity relationship (QSAR) analyses have been performed to analyze the basis for the antigelling activity of a series of aryl-substituted alanine analogs, including both phenylalanine and tryptophan analogs. We find that these two groups of compounds should be treated separately, probably due to the difference in shape between the phenyl and indole rings in the respective side chains. For the phenylalanine analogs, the hydrophobicity of the side chain, as measured by the pi constants of the aromatic ring and their substituents, explains about 50% of the variance in antigelling activity. The square of the aromatic dipole moment and the steric overlap volume, as obtained from three dimensional molecular shape analysis, account for an additional 20% and 10% of the variance, respectively. For the tryptophan analogs, the majority of the variance is explained either by the square of the aromatic dipole moment (70%) or by the steric overlap volume (60%), with the two descriptors being highly correlated. This result suggests that the tryptophan analogs exhibit a relatively tight steric fit within their binding sites. The separate QSAR's of phenylalanine and tryptophan analogs also suggest that these two groups of compounds may bind to hemoglobin through different mechanisms or at different sites. For phenylalanine analogs, the hydrophobic interaction is dominant, and the dipole-dipole interaction and steric effects contribute to lesser extents. For the tryptophan analogs, the dipole-dipole interaction prevails with a high degree of steric shape complimentarity, but without any significant contribution from hydrophobic interactions. This information should assist in the future development of more specific and effective agents.

Alanine↗
PubMed1989

Quantitative detection of rapid motions in spectrin by NMR.

Previous high resolution proton NMR data on human erythrocyte spectrin molecules has indicated the existence of regions exhibiting rapid internal motions within the intact molecules [L. W.-M. Fung, H.-Z. Lu, R. P. Hjelm, jr, M. E. Johnson, FEBS Lett., 197, 234 (1986)]. We have extended the studies by developing quantitative NMR methods to determine the fraction of spectrin protons exhibiting rapid internal motions, in both the isolated molecule and within the spectrin-actin network. Using both one-pulse and spin echo pulse sequences, we find that the fraction of the protons in rapid motion is about 15% of the total protons in the spectrin molecule at 37 degrees C in phosphate buffer with 150 mM NaCl at pH 7.4. Quantitative information on these rapid motions will be important in understanding the structural, mechanical and functional properties of spectrin molecules, as well as in understanding filamentous protein structures in general.

Erythrocyte Membrane↗
PubMed1989

Converging evidence for identification of recurrent relationship themes: comparison of two methods.

The therapeutic process is complex, and researchers and clinicians alike search for organizing principles or underlying structures that will reduce this complexity and thereby augment the efficacy of their respective endeavors. As other papers in this issue indicate, one such organizing principle is the concept of a recurring relationship theme that can be identified in the patient's descriptions of current and past relationships, as well as observed in the patient's interaction with the therapist. This concept has its origins in Freud's discovery of the transference phenomenon (1912), wherein the patient reenacts early relationships with significant others in the relationship with the analyst, and in Sullivan's interpersonal theory of psychiatry, with its central tenet that "personality is the relatively enduring pattern of recurrent interpersonal situations which characterize a human life" (1953, pp. 110-11). In the psychoanalytic and interpersonal therapies, these recurrent interpersonal themes, associated with the patient's difficulty in living and characterized as self-defeating and self-perpetuating, can potentially serve three main purposes: diagnosing and describing patients' difficulties, focusing therapeutic interventions, and measuring change on an individual basis. However, until recently, research on transference and rigidity of interpersonal style has been hampered by the lack of objective and clinically relevant measures for quantifying this clinical phenomenon (Kiesler 1986; Luborsky and Spence 1978). Luborsky (1977) developed the first reliable method for operationalizing the transference concept. Since then, as the companion papers in this issue point out, several different methods have been developed (e.g., Gill and Hoffman 1982; Horowitz 1979; Schacht et al. 1984). Although these methods differ in the postulated structural composition or components of the transference theme or recurrent relationship theme, they operate from similar methods of assessment. This paper presents the results of an initial investigation into convergent validity (Cronbach and Meehl 1955) of two of the major relationship theme methods--the Core Conflictual Relationship Theme (CCRT) of Luborsky and colleagues (Luborsky 1977), and the Cyclical Maladaptive Pattern (CMP: formerly called the "dynamic focus") of the Vanderbilt group (Schacht et al. 1984; Schacht and Henry, in press). In our investigation, developers of the approaches independently applied their methods to the same interview with a depressed patient. It was hypothesized that aside from differences due to the structural composition, the two methods would identify a similar relationship theme.

Adult↗
PubMed1989

Quantitative measurements of hip strength in different age groups.

The purpose of this study was to develop a clinically useful method of assessing the strength of the hip musculature and to develop a normal data base with this technique. The strength of 72 subjects aged 20-81 years (37 women and 35 men) was measured through the use of a modified Cybex II with an upright stabilization frame for testing sagittal and frontal plane motions; transverse plane motions of internal and external rotation were tested in the seated position. The subjects were tested at multiple isokinetic speeds and isometric angles. Regardless of age or gender, hip extensors were the strongest muscle group, following by flexors, adductors, abductors, and rotators. As the velocity of exercise increased, the magnitude of the torques produced decreased. Demographically, younger men produced the greatest torques and older women the lowest. The strength values of older men and younger women were similar. The results have clinical implications for objective assessment of strength in pathologic patient populations.

Adult↗
PubMed1989

CME and MSNJ.

Explore the source record for details and available documents.

Accreditation↗
PubMed1988

The design and synthesis of mimetics of peptide beta-turns.

The synthesis of an 11 membered ring bis-lactam, a system which is designed as a conformationally restricted mimetic of type I and type II beta-turns is described. Computer assisted molecular modeling was used to compare the predicted low energy conformers of the turn mimetic with idealized type I and type II turn structures. Initial computational analysis indicates that the basic ring structure will provide an excellent foundation for the development of a varieity of beta-turn mimetics.

Designer Drugs↗
PubMed1988

Four base-pair DNA deletion in human A gamma globin-gene promoter associated with low A gamma expression in adults.

Fetal haemoglobin (alpha 2 gamma 2) is predominant in red cells of the fetus and newborn baby, and is largely replaced after birth by adult haemoglobin (alpha 2 beta 2). The two types of gamma chains (A gamma and G gamma) are generally less than 1% of total beta-like chain in adults, and the G gamma: A gamma ratio is typically 40:60. Higher G gamma values (greater than 50% of gamma chain) are frequently associated with a T for C nucleotide substitution 158 base pairs 5' of the G gamma Cap site (-158). The first exception to this rule was a beta o-thalassaemia in a Black family that was associated with about 60% G gamma in heterozygotes. A DNA fragment containing the G gamma and A gamma genes of the high G gamma haplotype of this case has now been cloned. DNA sequencing from -383 to the Cap site showed no differences from normal for the G gamma gene, except for C at -158. For the A gamma gene, however, a deletion of four base pairs (AGCA) at -222 to -225 was found. It is hypothesized that this deletion causes reduced A gamma globin gene expression in adults, which suggests that promoter elements important for the regulation of fetal haemoglobin expression in adults extend upstream at least to -225.

Adult↗
PubMed1988

Immunoglobulin kappa light chain variable region gene complex organization and immunoglobulin genes encoding anti-DNA autoantibodies in lupus mice.

We have investigated the genetic origin of autoantibody production in several strains of mice that spontaneously develop a systemic lupus erythematosus-like disease. Restriction fragment length polymorphism analyses of gene loci encoding kappa light chain variable regions (Igk-V) demonstrated, as shown previously for the Ig heavy chain locus, that autoantibody production and disease occur in different Igk-V haplotypes. Moreover, autoimmune mice with known genetic derivation inherited their Igk-V loci essentially unaltered from their nonautoimmune ancestors. New Zealand black lupus mice, with unknown genetic derivation, had a possibly recombinant Igk-V haplotype, composed of V kappa loci that were primarily indistinguishable from those of nonautoimmune strains from either of the two potential donor haplotypes. The heavy and light chain gene segments (variable, diversity, joining) encoding anti-DNA antibodies were diverse and often closely related, or even identical, to those found in antibodies to foreign antigens in normal mice. Only 1 of 11 sequenced variable region genes could not be assigned to existing variable region gene families; however, corresponding germline genes were present in the genome of normal mice as well. These data argue against abnormalities in the genes and mechanisms generating antibody diversity in lupus mice and suggest a remarkable genetic and structural diversity in the generation of anti-DNA binding sites.

Amino Acid Sequence↗
PubMed1987

Saturation-transfer electron paramagnetic resonance detection of anisotropic motion by sickle hemoglobin molecules in the polymer state.

The motional behavior of spin-labeled deoxygenated sickle hemoglobin has been studied by using both 9- and 35-GHz saturation-transfer electron paramagnetic resonance (EPR). Using spectral subtraction techniques and saturation-transfer EPR parameter correlation plots, we find that the saturation-transfer EPR spectra for the sickle hemoglobin gel state at high temperature and high hemoglobin concentration cannot be described as a simple superposition of spectra from immobilized hemoglobin plus solution-state hemoglobin but instead suggest that the individual sickle hemoglobin molecules exhibit limited, anisotropic, rotational oscillation within the polymer fiber. The spectra also imply that the symmetry axis for sickle hemoglobin rotational oscillation is approximately coincident with the nitroxide z axis of the covalently attached spin-label. We suggest that this anisotropic rotational motion may be produced by one or two of the known intermolecular contact sites within the sickle hemoglobin fiber acting as strong intermolecular binding sites, and producing "motional alignment" within the fiber; determining the location of the strong binding site should be important in focusing the future development of antisickling agents.

Electron Spin Resonance Spectroscopy↗
PubMed1987

The genetic origin of murine lupus-associated autoantibodies.

Systemic lupus erythematosus and rheumatoid arthritis in human and murine systems are characterized by circulating autoantibodies and immune complex deposition in various organs causing tissue damage and disease. To define the molecular and clonotypic origin of these anti-self responses, and to determine whether abnormalities in Ig genes or somatic mechanisms generating autoantibody diversity may contribute to lupus etiology, we performed molecular analyses of the Ig germline gene organization and the Ig gene segments expressed in monoclonal autoantibodies from autoimmune mice. Comparative restriction fragment length polymorphism analysis of a large number of Ig gene loci from autoimmune and normal mice indicated that (a) lupus can develop in different Ig heavy and kappa light chain variable region gene haplotypes, and (b) the Ig germline genes in lupus mice might be normal. To determine whether autoantibodies are encoded by unique Ig gene segments present in the normal germline repertoire, but not expressed in exogenous responses, we compared nucleic acid sequences encoding lupus autoantibodies and antibodies against foreign antigens. Similar, and in some instances even identical, gene segments were expressed in both types of antibodies, indicating that anti-self and anti-foreign responses use the same, or at least an overlapping, germline gene repertoire. A large variety of Ig variable, diversity, and joining gene segments encoded these autoantibodies with different specificities. Hence, the overall murine lupus-associated anti-self response may be essentially unrestricted. Furthermore, limited evidence has been obtained that both germline genes and somatically mutated genes encode autospecificity, making gross abnormalities in mechanisms for somatic mutation of Ig variable genes unlikely.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

In vitro system for molybdopterin biosynthesis.

A high-Mr fraction present in chl+ and chlA1 strains of Escherichia coli synthesizes molybdopterin (MPT) from the low-Mr fraction of several MPT-deficient mutants. Using this in vitro complementation as an assay, we have partially characterized the high-Mr fraction as a protein, termed MPT converting factor, of Mr 45,000, distinguishable from the Mo cofactor carrier protein of similar Mr by its absolute requirement for the low-Mr fraction of a non-chlA1 mutant in the nit-1 reconstitution assay. MPT converting factor was rapidly inactivated in the absence of a reduced sulfhydryl compound. Anaerobic incubation of MPT converting factor with trypsin destroyed its activity. High-performance liquid chromatographic analysis of alkaline KMnO4 oxidation products demonstrated that the factor did not contain any bound pterin. Since mutants lacking MPT converting factor are not auxotrophs for folate or riboflavin, the factor appears to be distinct from known pteridine biosynthetic enzymes in E. coli. We have partially purified and characterized the low-Mr fractions as probable MPT precursors. Several distinct precursors were separable by high-performance liquid chromatography. Like MPT activity, precursor activity was oxygen sensitive. Precursor activity was not correlated with levels of L-threo-neopterin, a major pterin of unknown function in E. coli. Precursor activity was correlated with levels of a new 6-alkylpterin, compound Z, produced by acidic iodine oxidation. Compound Z has the properties expected of an oxidized MPT precursor.

Chromatography, High Pressure Liquid↗
PubMed1987

Involvement of chlA, E, M, and N loci in Escherichia coli molybdopterin biosynthesis.

All molybdenum enzymes except nitrogenase contain a common molybdenum cofactor, whose organic moiety is a novel pterin called molybdopterin (MPT). To assist in elucidating the biosynthetic pathway of MPT, two MPT-deficient mutants of Escherichia coli K-12 were isolated. They lacked activities of the molybdenum enzymes nitrate reductase and formate dehydrogenase, did not reconstitute apo nitrate reductase from a Neurospora crassa nit-1 strain, and did not yield form A, a derivative of MPT. By P1 mapping, these two mutations mapped to chlA and chlE, loci previously postulated but never definitely shown to be involved in MPT biosynthesis. The two new mutations are in different genetic complementation groups from previously isolated chlA and chlE mutations and have been designated as chlM and chlN (closely linked to chlA and chlE, respectively). The reported presence of Mo cofactor activity in the chlA1 strain is shown to be due to in vitro synthesis of MPT through complementation between a trypsin-sensitive macromolecule from the chlA1 strain and a low-molecular-weight compound from the nit-l strain.

Chromatography, High Pressure Liquid↗
PubMed1986

Interaction of a spin-labeled phenylalanine analogue with normal and sickle hemoglobins: detection of site-specific interactions through spin-label-induced 1H NMR relaxation.

In a preliminary report, we have previously shown that N-[(2,2,5,5-tetramethyl-1-oxypyrrolidin-3-yl)carbonyl]-L-phenyl ala nine tert-butyl ester (SL-Phe) exhibits specific binding to hemoglobin and an antiaggregation activity more than 2 orders of magnitude greater than that of phenylalanine [Lu, H.-Z., Currie, B. L., & Johnson, M. E. (1984) FEBS Lett. 173, 259-263]. Transverse 1H NMR relaxation measurements have been used to investigate the interaction of SL-Phe with hemoglobin molecules by use of the resonances assigned to the C2 protons of the beta 2 His, the beta 143 His, and the beta 146 or beta 97 His residues as intrinsic probes. Distance calculations using the paramagnetically induced relaxation data suggest that the SL-Phe binding site is approximately 12-16 A away from the C2 protons of the beta 2 His and the beta 146 or beta 97 His residues in the (carbonmonoxy)hemoglobin tetramer; for deoxyhemoglobin, the distances are approximately 14-17 A between the SL-Phe binding site and the C2 protons of the beta 2 His, the beta 143 His, and the beta 146 His residues. Calculations using the (carbonmonoxy)hemoglobin crystal atomic coordinates only restrict the probable SL-Phe binding region to the full F and H helices of the beta-chain and a small section of the alpha-chain. For deoxyhemoglobin, the distance calculations provide greater restrictions on the probable binding region, limiting it to small sections of the beta-chain F, G, and H helices near the EF bend and to a few residues on the alpha-chain.(ABSTRACT TRUNCATED AT 250 WORDS)

Affinity Labels↗