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J A King

Publications and source records attributed to J A King.

At least 19 recordsLinked to original sources
PubMed1992

Molecular thermodynamic model to predict the alpha-helical secondary structure of polypeptide chains in solution.

The native state of a protein molecule in aqueous solutions represents one of the lowest states of Gibbs energy [Anfinsen, C.B. (1973) Science 181, 223-230]. Much progress has been made about the rules of protein folding [King, J. (1989) Chem. Eng. News 67, 32-54] and the dominant forces in protein folding [Dill, K.A. (1990) Biochemistry 29, 7133-7155]. However, the quantitative contributions of different Gibbs energy terms to protein stability remains a controversial issue [Moult, J., & Unger, R. (1991) Biochemistry 30, 3816-3824]. A molecular thermodynamic model has been proposed for the Gibbs energy of folding a residue in aqueous homopolypeptides from a random-coiled state to either the alpha-helix state or the beta-sheet state [Chen, C.-C., Zhu, Y., King, J.A., & Evans, L.B. (1992) Biopolymers 32, 1375-1392]. In this work, we present a generalization of the molecular thermodynamic model for the Gibbs energy of folding natural and synthetic heteropolypeptides from random-coiled conformations into alpha-helical conformations. The generalized model incorporates the intrinsic folding potential due to residue-solvent interactions, the cooperative folding effect due to residue-residue interactions, and the location and length of alpha-helices. The utility of the model was demonstrated by examining the stability of alpha-helical conformations of a number of natural polypeptides including C-peptide (residues 1-13) and S-peptide (residues 1-20) of RNase A (bovine pancreatic ribonuclease A), the P alpha fragment in BPTI (bovine pancreatic trypsin inhibitor), and synthetic polypeptides (the copolymers of different amino acid residues) including alanine-based peptides (16 or 17 residues long) in water. The computed Gibbs energies correspond well with the experimental data on helicity. The results also accounted for the effects of amino acid substitution and temperature on the stability of alpha-helical conformations of the test polypeptides.

Amino Acid Sequence↗
PubMed1992

The IL-6 signal transducer, gp130: an oncostatin M receptor and affinity converter for the LIF receptor.

Leukemia inhibitory factor (LIF) and interleukin-6 (IL-6) are multifunctional cytokines with many similar activities. LIF is structurally and functionally related to another cytokine, Oncostatin M (OSM), that binds to the high-affinity LIF receptor but not to the low-affinity LIF receptor. A complementary DNA was isolated that encodes the high-affinity converting subunit of the LIF receptor. The converter conferred high-affinity binding of both LIF and OSM when expressed with the low-affinity LIF receptor and is identical to the signal transducing subunit of the IL-6 receptor, gp130. The gp130 subunit alone confers low-affinity binding of OSM when expressed in COS-7 cells. This receptor system resembles the high-affinity receptors for granulocyte-macrophage colony-stimulating factor, IL-3, and IL-5, which share a common subunit.

Animals↗
PubMed1992

A molecular thermodynamic approach to predict the secondary structure of homopolypeptides in aqueous systems.

Under physiological conditions, many polypeptide chains spontaneously fold into discrete and tightly packed three-dimensional structures. The folded polypeptide chain conformation is believed to represent a minimum Gibbs energy of the system, governed by the weak interactions that operate between the amino acid residues and between the residues and the solvent. A semiempirical molecular thermodynamic model is proposed to represent the Gibbs energy of folding of aqueous homopolypeptide systems. The model takes into consideration both the entropy contribution and the enthalpy contribution of folding homopolypeptide chains in aqueous solutions. The entropy contribution is derived from the Flory-Huggins expression for the entropy of mixing. It accounts for the entropy loss in folding a random-coiled polypeptide chain into a specific polypeptide conformation. The enthalpy contribution is derived from a molecular segment-based Non-Random Two Liquid (NRTL) local composition model [H. Renon and J. M. Prausnitz (1968) AIChE J., Vol. 14, pp. 135-142; C.-C. Chen and L. B. Evans (1986) AIChE J., Vol. 32, pp. 444-454], which takes into consideration of the residue-residue, residue-solvent, and solvent-solvent binary physical interactions along with the local compositions of amino acid residues in aqueous homopolypeptides. The UNIFAC group contribution method [A. Fredenslund, R. L. Jones, and J. M. Prausnitz (1975) AIChE J., 21, 1086-1099; A. Fredenslund, J. Gmehling, and P. Rasmussen (1977) Vapor-Liquid Equilibrium Using UNIFAC, Elsevier Scientific Publishing Company, Amsterdam], developed originally to estimate the excess Gibbs energy of solutions of small molecules, was used to estimate the NRTL binary interaction parameters. The model yields a hydrophobicity scale for the 20 amino acid side chains, which compares favorably with established scales [Y. Nozaki and C. Tanford (1971) Journal of Biological Chemistry, Vol. 46, pp. 2211-2217; E. B. Leodidis and T. A. Hatton (1990) Journal of Physical Chemistry, Vol. 94, pp. 6411-6420]. In addition, the model generates qualitatively correct thermodynamic constants and it accurately predicts thermodynamically favorable folding of a number of aqueous homopolypeptides from random-coiled states into alpha-helices. The model further facilitates estimation of the Zimm-Bragg helix growth parameter s and the nucleation parameter sigma for amino acid residues [B. H. Zimm and J. K. Bragg (1959) Journal of Chemical Physics, Vol. 31, pp. 526-535]. The calculated values of the two parameters fall into the ranges suggested by Zimm and Bragg.

Models, Molecular↗
PubMed1992

Triphasic waves and spike wave stupor.

Triphasic waves are usually thought of as indicating a metabolic encephalopathy. Recent investigations have added nonmetabolic etiologies to the differential diagnosis of triphasic waves. Seizures are not generally thought of as associated with triphasic waves. Similarities in the appearance of records with encephalopathies and continuous triphasic waves and those of some patients with the Lennox-Gastaut syndrome have been noted. We presented a case which suggests that the presence of TW in a patient with a metabolic encephalopathy might suggest petit mal status epilepticus.

Aged↗
PubMed1991

Differential effects of prenatal and postnatal ACTH or nicotine exposure on 5-HT high affinity uptake in the neonatal rat brain.

These studies were designed to examine the differential effects of prenatal or postnatal administration of ACTH 1-39 and nicotine, on 5-HT high affinity uptake in brainstem and hippocampal synaptosomes. ACTH was administered prenatally (to pregnant dams) and postnatally to the neonates. Postnatal administration of ACTH significantly increased high-affinity 5-HT uptake in the hippocampus and especially the brainstem at both 7 and 21 days after birth. Prenatal ACTH, on the other hand, transiently increased 5-HT uptake in only the brainstem at 7 days, a change that was reversed at 21 days. While the effects of postnatal nicotine administration were essentially the same as those of postnatal ACTH treatment, prenatal nicotine, unlike ACTH, did not alter 5-HT uptake in 7-day-old rats but did reduce uptake in both tissues at 21 days. The observation that postnatal nicotine mimics the effects of postnatal ACTH and that nicotine stimulates ACTH release, suggests that the postnatal effects of nicotine may be exerted through ACTH.

Adrenocorticotropic Hormone↗
PubMed1991

Inheritance of the equine Tf F3 allele.

The inheritance of the equine Tf F3 allele was examined in 39 parent-offspring combinations. For 26 of the cases the allele inherited by the offspring from the heterozygous parent could be determined. The proportion of individuals that inherited the F3 variant compared to the alternative allele was exactly 1:1. In five cases the parental phenotype was identical to that of the offspring. For the remaining eight cases the parent was homozygous for the F3 allele and all offspring had the F3 allele. The results were consistent with Mendelian inheritance.

Alleles↗
PubMed1990

Structural organization of the genes for murine and human leukemia inhibitory factor. Evolutionary conservation of coding and non-coding regions.

Leukemia inhibitory factor, LIF, is a glycoprotein with multiple activities in both the adult and the embryo. LIF appears to be encoded by a unique gene in both mouse and man, although the 3'-untranslated region of the mouse LIF gene gives a complex hybridization pattern on Southern blots. The complete nucleotide sequences of both the murine and human LIF genes and their flanking regions (8.7 and 7.6 kilobase pairs, respectively) were determined and compared. Both genes comprise three exons, two introns and an unusually long 3'-untranslated region (3.2 kilobase pairs), specificying a mRNA of approximately 4.1 kilobases. Two start sites of LIF-transcription were determined, by S1-nuclease protection and by a novel approach involving the polymerase chain reaction. S1-nuclease protection revealed a start site 60-64 base pairs upstream of the translational start codon and immediately downstream of a TATA box (TATATAAAT). The PCR approach identified a second transcriptional start site 160 base pairs 5' of the start codon and adjacent to a "TATA-like" element (CATAATTT). A comparison of the murine and human LIF gene sequences revealed a high degree of conservation in the coding regions and in segments of the untranslated and flanking regions. Seven segments displaying greater than 75% homology were identified, with the 5' and 3' ends of the transcription unit revealing the highest degree of homology. These conserved regions represents potential cis-acting control elements.

Amino Acid Sequence↗
PubMed1989

Chimeric analogues of vertebrate gonadotropin-releasing hormones comprising substitutions of the variant amino acids in positions 5, 7, and 8. Characterization of requirements for receptor binding and gonadotropin release in mammalian and avian pituitary gonadotropes.

Variant forms of mammalian gonadotropin-releasing hormone (GnRH) (pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly.NH2) are present in chicken ([Gln8] GnRH and [His5, Trp7, Tyr8]GnRH), salmon ([Trp7, Leu8]GnRH), and lamprey ([Tyr3, Leu5, Glu6, Trp7, Lys8] GnRH). To delineate the functional importance of the variant amino acids in positions 5, 7, and 8, the natural peptides and chimeric analogues were tested for gonadotropin-releasing activity and receptor-binding activity in rat, sheep, and chicken pituitaries. The results demonstrate that (i) the mammalian receptor has a high fidelity for Arg8 while the chicken receptor is less discriminatory and accepts basic or neutral amino acids in this position. Arg8 may contribute to conformational stabilization, and conformational constraint with D-Trp6 restored activity to analogues lacking Arg8 in the mammalian systems. D-Trp6 incorporation did not generally enhance activity in the chicken pituitary. (ii) His5 accompanying Arg8 in analogues markedly diminished activity in the chicken while gonadotropin-releasing activity was retained in the sheep pituitary. Receptor-binding activity was increased in the sheep indicating an uncoupling of receptor occupancy and activation. (iii) Substitution in position 7 is tolerated by the mammalian and chicken receptor. With Trp7-substituted analogues receptor-binding activity was relatively lower than gonadotropin-releasing activity in the sheep pituitary, suggesting an enhanced receptor activation by these analogues or the existence of different GnRH receptors.

Amino Acid Sequence↗
PubMed1989

Expression cloning of a receptor for human granulocyte-macrophage colony-stimulating factor.

Two cDNA clones encoding a receptor for human granulocyte-macrophage colony-stimulating factor (hGM-CSF-R) were isolated by expression screening of a library made from human placental mRNA. Pools of recombinant plasmid DNA were electroporated into COS cells which were then screened for their capacity to bind radioiodinated hGM-CSF using a sensitive microscopic autoradiographic approach. The cloned GM-CSF-R precursor is a 400 amino acid polypeptide (Mr 45,000) with a single transmembrane domain, a glycosylated extracellular domain and a short (54 amino acids) intracytoplasmic tail. It does not contain a tyrosine kinase domain nor show homology with members of the immunoglobulin super gene family, but does show some significant sequence homologies with receptors for several other haemopoietic growth factors, including those for interleukin-6, erythropoietin and interleukin-2 (beta-chain) and also to the prolactin receptor. When transfected into COS cells the cloned cDNA directed the expression of a GM-CSF-R showing a single class of affinity (KD = 2(-8) nM) and specificity for human GM-CSF but not interleukin-3. Messenger RNA coding for this receptor was detected in a variety of haemopoietic cells known to display hGM-CSF binding, and cross-linking experiments revealed a similar size for the glycosylated receptors in transfected COS and haemopoietic cells.

Amino Acid Sequence↗
PubMed1989

Testing of Arg-8-gonadotropin-releasing hormone-directed antisera by immunological and immunocytochemical methods for use in comparative studies.

Three polyclonal antisera raised in rabbits against the mammalian molecular form of gonadotropin-releasing hormone (GnRH) were tested in enzyme-linked immunosorbent assays for crossreactivity with naturally occurring GnRHs and with GnRH analogues. Antisera were then tested immunocytochemically in order (i) to identify amino acids essential for the binding of each antiserum, and (ii) to evaluate the specificity of the immunocytochemical reaction in brain sections from various species of cyclostomes, amphibians, reptiles, and birds. Antiserum GnRH 80/1, recognizing mainly a discontinuous determinant including the NH2- and COOH-termini, crossreacts with GnRHs the molecular bending of which enables the spatial approach of both terminal amino acid residues. Antiserum GnRH 80/2, by requiring the COOH-terminus for binding and not tolerating substitutions by aromatic amino acids in the middle region of the molecule, recognizes chicken I GnRH, however, not the salmon form. The use of this antiserum is appropriate in species synthesizing the mammalian and/or the chicken I form of GnRH. GnRH antiserum 81/1 is specific mostly for mammalian GnRH. The results obtained by ELISAs are confirmed by immunocytochemical studies. A comparison between the results obtained in ELISA and in immunocytochemistry involving mammalian-, chicken I-, chicken II-, salmon-, and lamprey-directed GnRH antisera resulted in the following conclusions: (1) An antiserum recognizing the discontinuous antigen determinant including both NH2- and COOH-termini may be reactive in most vertebrate brain sections thus being appropriate for phylogenetically directed immunocytochemical studies. (2) Moreover, this discontinuous determinant seems to be immunocytochemically reactive in all parts of the neurons in the GnRH system, whereas, in some species, determinants located in the middle region of the molecule(s) tend to become reactive only during the axonal transport. (3) A crossreaction between tissue-bound antigen and antibodies recognizing the above cited discontinuous determinant indicates an appropriate bending of the molecule even in case of severe molecular differences, e.g., in lamprey form of GnRH. (4) It follows that in phylogenetic studies, an immunologically well characterized antiserum can be substituted for a species-directed antiserum.

Amphibians↗
PubMed1989

ACTH modulation of nerve development and regeneration.

(1) The availability of short amino acid sequences of the naturally occurring ACTH 1-39 molecule has made it possible to separate the corticotropic characteristics of the parent molecule from its neurotrophic effects. Potent neurotrophic fragments are ACTH 4-10, an analog of ACTH 4-9 (Org 2766), and alpha-MSH (ACTH 1-13), peptide fragments that do not evoke corticosteroid secretion, yet clearly affect both the development and regeneration of peripheral nerve. (2) Early postnatal administration of either ACTH 4-10 or Org 2766 accelerates the neuromuscular development of the immature rat, increasing the contractile strength of the EDL muscle and inducing more rapid muscle contractions. Grasping strength and motor activity are increased; these are all changes indicative of more rapid neuromuscular maturation. Prenatal peptide treatment elicits a more complex pattern of response since administration early in gestation (GD 3-12) accelerates neuromuscular development whereas later administration (GD 13-21) decelerates maturation. (3) ACTH peptides have a similar accelerating effect on the morphology of the developing neuromuscular junction. At two weeks of age, nerve arborization is conspicuously increased by postnatal administration of either ACTH 4-10 or Org 2766, as is nerve terminal branching within the endplate itself. However, this is preceded by an initial depression of nerve branching in the 7-day-old rat pup. We conclude that while the developing neuromuscular system is sensitive to ACTH peptides, this susceptibility is age-related. The crucial role of these peptides may be limited to very brief, defined periods during which the peptides may interact with trophic or growth-associated substances, each of which may have its own decisive, circumscribed time frame of influence. (4) Perinatal administration of ACTH peptides affects CNS development. One measurable indication of this is an acceleration of eye opening. Early exposure to ACTH peptides has long-lasting effects on behavior, apparent when these animals are tested as adults. Increased spontaneous motor activity, heightened states of arousal and agitation, and changes in social behavior have been reported. Certain avoidance responses and tests of visual discrimination in male rats are improved by neonatal treatment with alpha-MSH. Overall motor activity is increased and the normal period of hyperactivity is initiated earlier. Male sexual behavior is decreased and sexually dimorphic behaviors in males are eliminated. alpha-MSH may alter the development of its own dopaminergic feedback circuitry while ACTH affects serotonin levels in the preoptic nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenocorticotropic Hormone↗
PubMed1989

Gonadal steroid modulation of signal transduction and luteinizing hormone release in cultured chicken pituitary cells.

The mechanism whereby gonadal steroids modulate GnRH-stimulated LH secretion by primary cultures of chicken pituitary cells was investigated. Estradiol (10(-8) M), testosterone (10(-7) M), and progesterone (10(-7) M) inhibited LH release stimulated by GnRH (10(-7) M) by 56%, 61%, and 53%, respectively, and the inhibitory effects required prolonged preincubation (24-48 h) with the steroids. The steroids inhibited the spike (0-3 min) and plateau (9-30 min) phases of LH release to a similar degree. The ED50 values of estradiol, testosterone, and progesterone for inhibition of GnRH-stimulated LH release were 7 x 10(-11), 2 x 10(-9), and 1 x 10(-9) M, respectively. Estradiol, testosterone, and progesterone inhibited the maximal LH response to GnRH, but the ED50 of GnRH (4 x 10(-9) M) was not altered by steroid pretreatment. Steroid pretreatment did not cause a change in cellular LH content, suggesting that the steroids do not inhibit LH synthesis. Combinations of two or three of the steroids were not additive, suggesting that all three steroids affect GnRH-stimulated LH release via the same mechanism. In experiments investigating their mechanism of action, the steroids inhibited LH release stimulated by GnRH and Ca2+ ionophore A23187, but generally had no effect on the responses to phorbol ester (12-O-tetradecanoylphorbol-13-acetate), forskolin, K+, Bay K8644, or veratridine. Estradiol inhibited GnRH-stimulated 45Ca2+ efflux, but its inhibitory effect on GnRH-induced inositol phosphate production was not significant. Estradiol had no effect on binding of 125I-[His5,D-Tyr6]GnRH to a pituitary cell preparation. These findings suggest that the site of steroid modulation of GnRH action is distal to binding of GnRH to its receptor, and that the inhibitory effects are exerted at two intracellular sites: 1) the coupling events linking receptor activation to mobilization of Ca2+, and 2) a site distal to Ca2+ mobilization.

Animals↗
PubMed1989

A second form of gonadotropin-releasing hormone (GnRH), with chicken GnRH II-like properties, occurs together with mammalian GnRH in marsupial brains.

GnRH peptides in the hypothalami of marsupials (tammar wallaby, short-nosed bandicoot, and eastern quoll) and a monotreme (echidna) were investigated by reverse phase HPLC and RIA with region-specific antisera. In the wallaby hypothalamic extract, a single form of GnRH was present, which eluted in the same position as synthetic mammalian GnRH on HPLC and was recognized by antibodies directed against the NH2- and COOH-termini of mammalian GnRH as well as by antibodies to the middle region. Two GnRH molecular forms were demonstrated in the bandicoot and quoll hypothalamic extracts. One form eluted in the same position as synthetic mammalian GnRH on HPLC and was quantified equally by two mammalian GnRH antisera. The second form eluted in the same position as synthetic chicken GnRH II and was recognized by specific antibodies to this molecule. Quantification of this immunoreactive peak with two chicken GnRH II antisera was not equal, suggesting that the peptide has similar properties to, but may not be identical to, chicken GnRH II. Immunoreactive GnRH was also detected in the echidna hypothalamic extract. These findings demonstrate that in some mammals more than one form of GnRH is present in the brain of a single species, as has previously been found in species from all nonmammalian vertebrate classes. The finding in marsupial brain of a peptide with properties of chicken GnRH II, which has previously been reported in species of Aves, Reptilia, Amphibia, Osteichthyes, and Chondrichthyes, supports our hypothesis that this widespread structural variant may represent an early early evolved and conserved form of GnRH.

Aging↗
PubMed1988

Is nicotine depression of neonatal motor behavior exerted through ACTH release?

Prenatal exposure to nicotine tartrate (0.25 mg/kg/pregnant female, gestation days 3 through 21.2x daily IP) markedly decreases ambulatory activity and the number of stop and go movements in 15 day old neonatal rats. Postnatal nicotine tartrate administration alone (0.05 mg/kg SC daily from birth) does not affect these movements nor does it further the motor depression induced by prenatal nicotine treatment. Thus the critical period of neural susceptibility to nicotine appears to be during prenatal life. However, when nicotine is given both pre- and postnatally, horizontal movements are increased in the 15 day old animals, an increase that may be due to inhibition of other types of movement. These alterations in motor behavior are correlated with sharp increases in plasma ACTH levels. As our previous studies [1,25] have shown ACTH to affect neonatal motor behavior, it is suggested that nicotine-evoked ACTH release may mediate some of the motor responses attributed to the drug.

Adrenocorticotropic Hormone↗
PubMed1988

Maturational changes in neonatal rat motor system with early postnatal administration of nicotine.

Experiments were designed to assess the effects of chronic maximum 'smoking dose' nicotine administration on neonatal motor behavior and neuromuscular structural maturation. Thus, Sprague-Dawley rat neonates received daily subcutaneous injections of nicotine (0.05 mg/kg/day) from postnatal days 1 to 14. Motor behavior (ambulations, stop and go movements) was not affected, but a marked increase in grasping duration resulted, indicating increased neuromuscular maturation. Concomitantly, neuromuscular morphological and dynamic contractile changes were observed in the in situ extensor digitorum longus (EDL) muscle. The EDL muscle showed accelerated morphological dimensions of the endplate at postnatal day 7 and a more rapid twitch at 2 weeks of age. The results suggest that this maximum 'smoking dose' of nicotine induces time-dependent maturational changes in the neuromuscular model.

Animals↗
PubMed1988

Molecular cloning and expression of the human homologue of the murine gene encoding myeloid leukemia-inhibitory factor.

A human homologue of the recently cloned murine leukemia-inhibitory factor (LIF) gene was isolated from a genomic library by using the murine cDNA as a hybridization probe. The nucleotide sequence of the human gene indicated that human LIF has 78% amino acid sequence identity with murine LIF, with no insertions or deletions, and that the region of the human gene encoding the mature protein has one intervening sequence. After oligonucleotide-mediated mutagenesis, the mature protein-coding region of the LIF gene was introduced into the yeast expression vector YEpsec1. Yeast cells transformed with the resulting recombinant could be induced with galactose to produce high levels of a factor that induced the differentiation of murine M1 leukemic cells in a manner analogous to murine LIF. This factor competed with 125I-labeled native murine LIF for binding to specific cellular receptors on murine cells, compatible with a high degree of structural similarity between the murine and human factors.

Amino Acid Sequence↗