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Biomedical subjects

A C Young

Publications and source records attributed to A C Young.

At least 37 records · Page 2Linked to original sources
PubMed1994

Structural studies on human muscle fatty acid binding protein at 1.4 A resolution: binding interactions with three C18 fatty acids.

BACKGROUND: Muscle fatty acid binding protein (M-FABP) is one of a family of cytosolic lipid-binding proteins involved in fatty acid processing. In order to investigate the precise interactions between M-FABP and its ligands and to understand the structural basis of differential binding affinity, we have compared the structures of M-FABP in complex with three C18 fatty acids. RESULTS: We describe the crystal structures of M-FABP in complex with n-octadecanoate (stearate), trans-delta 9-octadecenoate (elaidate) and cis-delta 9-octadecenoate (oleate). These structures were refined using least-squares positional and anisotropic temperature factor refinement to final R-factors of 11.4%, 12.1% and 13.2% respectively for all the data between 8.0 A and 1.4 A resolution. CONCLUSIONS: Stearate, elaidate and oleate each adopt highly similar U-shaped conformations when they bind to M-FABP within a large interior binding cavity, which also contains 13 ordered water molecules. The atomic structure of the protein is virtually identical, regardless of the nature of the bound ligand. The fatty acid is thought to enter the interior cavity of the protein via a portal in its surface while interior solvent is released through a secondary opening. The ligand affinity can be correlated with the conformational energy and the solubility of the bound ligand.

Carrier Proteins↗
PubMed1994

The three-dimensional structure of H-2Db at 2.4 A resolution: implications for antigen-determinant selection.

Solution at 2.4 A resolution of the structure of H-2Db with the influenza virus peptide NP366-374 (ASNEN-METM) and comparison with the H-2Kb-VSV (RGY-VYQGL) structure allow description of the molecular details of MHC class I peptide binding interactions for mice of the H-2b haplotype, revealing a strategy that maximizes the repertoire of peptides than can be presented. The H-2Db cleft has a mouse-specific hydrophobic ridge that causes a compensatory arch in the backbone of the peptide, exposing the arch residues to TCR contact and requiring the peptide to be at least 9 residues. This ridge occurs in about 40% of the known murine D and L allelic molecules, classifying them as a structural subgroup.

Amino Acid Sequence↗
PubMed1994

Thermal expansion of hen egg-white lysozyme. Comparison of the 1.9 A resolution structures of the tetragonal form of the enzyme at 100 K and 298 K.

The average structural and dynamic properties of tetragonal hen egg-white lysozyme have been compared, in structures refined at 1.9 A resolution, using data collected at 100 K and 298 K. The molecule expands by 1.8% over this temperature range with the expansion occurring primarily in its small sub-atomic-sized spaces in an anisotropic manner. Hen egg-white lysozyme consists of two domains: domain 1 (residues 40 to 88) is composed primarily of beta-sheet and is observed to expand by only 0.3%; domain 2 (residues 1 to 39 and 89 to 129) is chiefly alpha-helix and is observed to expand by 2.2%. This is consistent with previous observations that proteins composed primarily of alpha-helix expand more with temperature than do those composed primarily of beta-sheet. The largest movement in the molecule is undergone by the two domains of the structure that move further apart as the temperature is raised. This motion is not a cleft opening but rather consists of a tilt by 2.3 degrees of domain 1 away from domain 2. Within the individual domains the largest movement is undergone by loop T1 of domain 2, consisting of residues 17 to 23. This loop moves in the opposite direction to the rest of the molecule as the temperature is raised. Average temperature factors for the room-temperature and low-temperature structures are 15.2 A2 and 8.1 A2, respectively, when all protein atoms are considered, while these values are 14.0 A2 and 7.8 A2, when only main-chain atoms (N, C alpha, C) are taken into account. An examination of the main-chain averaged B-factor per residue shows that residues involved in intermolecular protein-protein contacts, with symmetry-related molecules, have somewhat lower B-factors than the average and undergo smaller than average changes in B-factor as the temperature is lowered.

Amino Acid Sequence↗
PubMed1992

Crystal structure of the major histocompatibility complex class I H-2Kb molecule containing a single viral peptide: implications for peptide binding and T-cell receptor recognition.

To study the structure of a homogenous major histocompatibility complex (MHC) class I molecule containing a single bound peptide, a complex of recombinant mouse H-2Kb, beta 2-microglobulin (beta 2m), and a fragment of the vesicular stomatitis virus (VSV) nuclear capsid protein, VSV-(N52-59) octapeptide (Arg-Gly-Tyr-Val-Tyr-Gln-Gly-Leu), was prepared by exploiting a high-yield bacterial expression system and in vitro cocomplex formation. The structure of mouse H-2Kb revealed its similarity to three human class I HLA molecules, consistent with the high primary sequence homology and common function of these peptide-presenting molecules. Electron density was located in the peptide-binding groove, to which a single peptide in a unique conformation was unambiguously fit. The peptide extends the length of the groove, parallel to the alpha-helices, and assumes an extended, mostly beta-strand conformation. The peptide is constrained within the groove by hydrogen bonding of its main-chain atoms and by contacts of its side chains with the H-2Kb molecule. The amino-terminal nitrogen atom of the peptide forms a hydrogen bond with the hydroxyl group of Tyr-171 of H-2Kb at one end of the groove, while the carboxyl-terminal oxygen forms a hydrogen bond with the hydroxyl group of Tyr-84 at the other end. Since the amino acids at both ends are conserved among human and mouse MHC molecules, this anchoring of each end of the peptide appears to be a general feature of peptide-MHC class I molecule binding and imposes restrictions on its length. The side chains of residues Tyr-3, Tyr-5, and Leu-8 of the VSV octapeptide fit into the interior of the H-2Kb molecule with no appreciable surface exposure, a finding in support of previous biological studies that showed the importance of these residues for binding. Thus, the basis for binding of specific peptide sequences to the MHC class I molecule is the steric restriction imposed on the peptide side chains by the architecture of the floor and sides of the groove. The side chains of Arg-1, Val-4, and Gln-6 and the main-chain of Gly-7 of the octapeptide are exposed on the surface of the complex, thus confirming their availability for T-cell receptor contact, as previously demonstrated by T-cell recognition experiments.

Amino Acid Sequence↗
PubMed1990

Structure of a cannabinoid receptor and functional expression of the cloned cDNA.

Marijuana and many of its constituent cannabinoids influence the central nervous system (CNS) in a complex and dose-dependent manner. Although CNS depression and analgesia are well documented effects of the cannabinoids, the mechanisms responsible for these and other cannabinoid-induced effects are not so far known. The hydrophobic nature of these substances has suggested that cannabinoids resemble anaesthetic agents in their action, that is, they nonspecifically disrupt cellular membranes. Recent evidence, however, has supported a mechanism involving a G protein-coupled receptor found in brain and neural cell lines, and which inhibits adenylate cyclase activity in a dose-dependent, stereoselective and pertussis toxin-sensitive manner. Also, the receptor is more responsive to psychoactive cannabinoids than to non-psychoactive cannabinoids. Here we report the cloning and expression of a complementary DNA that encodes a G protein-coupled receptor with all of these properties. Its messenger RNA is found in cell lines and regions of the brain that have cannabinoid receptors. These findings suggest that this protein is involved in cannabinoid-induced CNS effects (including alterations in mood and cognition) experienced by users of marijuana.

Amino Acid Sequence↗
PubMed1988

Cloning and expression of the human and rat m5 muscarinic acetylcholine receptor genes.

The human and rat genes for a fifth muscarinic receptor have been cloned and expressed in mammalian cells. The 532 amino acid human protein has 89% sequence identity to the 531 amino acid rat protein and is most closely related to the m3 receptor. Both proteins are encoded by single exons. The receptor has intermediate affinity for pirenzepine and low affinity for AF-DX 116, and it increases metabolism of phosphatidylinositol when stimulated with carbachol. Expression of mRNA has yet to be observed in brain or selected peripheral tissues, suggesting that either it is substantially less abundant than m1-m4 or its distribution is quite different.

Amino Acid Sequence↗
PubMed1987

Identification of a family of muscarinic acetylcholine receptor genes.

Complementary DNAs for three different muscarinic acetylcholine receptors were isolated from a rat cerebral cortex library, and the cloned receptors were expressed in mammalian cells. Analysis of human and rat genomic clones indicates that there are at least four functional muscarinic receptor genes and that these genes lack introns in the coding sequence. This gene family provides a new basis for evaluating the diversity of muscarinic mechanisms in the nervous system.

Amino Acid Sequence↗
PubMed1987

A cDNA encoding the precursor of the rat neuropeptide, neurokinin B.

We have isolated a cDNA clone from a rat cerebral cortex library which encodes the 116 amino acid precursor of the neuropeptide, neurokinin B. The precursor has 68% amino acid homology to the bovine precursor and encodes a single peptide of the tachykinin family. Except for possible small variations at both ends of the message, there appears to be only a single species of neurokinin B mRNA in rat cerebral cortex. In situ hybridization histochemistry indicates that the message is widely distributed in the rat brain in a pattern distinct from that of substance P message.

Amino Acid Sequence↗
PubMed1985

Enhancement of Clq binding activity by IgM rheumatoid factor.

Clq binding activity (ClqBA) averaged 18.1 +/- 14.5% (1 SD) in 28 rheumatoid arthritis (RA) sera (normal sera = 3.9 +/- 0.4%). Further analysis indicated that rheumatoid factor (RF) positive [RA (+)] sera averaged 30.4% ClqBA, significantly greater than the 3.9% ClqBA in RA RF negative [RA(-)] sera (p less than 0.01). In the RA(+) sera, RF titer correlated with ClqBA (r = +0.73). Addition of IgM RF to sera of normal, SLE, and RA(-) patients, as well as to aggregated IgG and reduced and alkylated aggregated IgG, resulted in significant increases in ClqBA, up to 14% in the latter group (p less than 0.01). Control IgM added to these same systems had no effect on ClqBA. IgM RF only slightly increased Clq binding of monomeric IgG.

Antigen-Antibody Complex↗
PubMed1983

Acute effects of steroids on immune complex profile of patients with systemic lupus erythematosus. Correlation of profile with development of target organ involvement.

Eleven patients with active systemic lupus erythematosus, previously untreated, were studied to 1) determine the acute effect of corticosteroids on circulating immune complex (CIC) levels and 2) correlate the initial CIC profile with the development of organ system involvement. Using serial measurements of CIC as detected by assays for cryoglobulins and binding to C1q, Raji cells, and rheumatoid factor, we found that levels of CIC change little during the first month of high dose daily steroid therapy, but they uniformly decrease to near normal by 6 to 12 months. High levels of CIC detected by Raji cell assay early in the course of systemic lupus erythematosus and before steroid therapy appear to be predictive of the development of chronic lupus nephritis (P less than 0.005).

Adult↗
PubMed1982

Is routine computerised axial tomography in epilepsy worth while?

The value of routine computerised axial tomography of the brain (CT scanning) was assessed in 220 consecutive patients with epilepsy or isolated seizures. Abnormal CT scans were found in more than half the patients with focal seizures associated with focal signs or a delta focus on the electroencephalogram (EEG). In patients without focal features the CT scan was normal in 94%. Only a quarter of the abnormalities found on CT scanning were potentially treatable by surgery, and only 10% of all the patients had their management changed as a result of CT scanning. In 3 patients with tumours the first scan had been normal. Careful clinical assessment and examination supported by an EEG remain of paramount importance in the management of epilepsy, and CT scanning should be reserved for patients with focal features.

Adolescent↗
PubMed1982

Glutamate stimulation of 45Ca uptake by rat striatal synaptosomes.

The effects of acidic excitatory amino acids and 60 mM K+ on 45Ca uptake by synaptosomes prepared from rat striatum were examined. Both glutamic acid and 60 mM K+ significantly stimulated the uptake of 45Ca and these effects were antagonized by 30 mM Mg2+ and 0.5 mM La3+ but not by 5 microM tetrodotoxin. Neither kainic acid nor N-methyl-D,L-aspartic acid significantly affected the uptake of 45Ca. The results suggest that glutamate may activate a presynaptic receptor that is directly linked to calcium channels.

Animals↗
PubMed1981

Laminar distribution of cholinergic markers in neocortex: effects of lesions.

The distribution of presynaptic markers for cholinergic and GABAergic neurons in the various layers of the lateral neocortex was determined with a technique in which sections of increasing depth horizontal to the pial surface were obtained on a frozen-stage microtome and analyzed for the markers. The specific activities of choline acetyltransferase and acetylcholinesterase had an uneven distribution in the cortex with lowest levels of activity associated with lamina II and III, whereas glutamate decarboxylase activity was highest in lamina II, III, and IV. Fetally-induced hypoplasia of the cortex resulted in an enrichment in both choline acetyltransferase and acetylcholinesterase activity in all layers with no significant change in the activity of glutamate decarboxylase. Lesion of the nucleus basalis-cortical cholinergic pathway resulted in marked reductions in the activities of acetylcholinesterase and choline acetyltransferase in all cortical layers and an elimination of the uneven distribution of these markers within the cortex. These results provide further evidence that acetylcholinesterase activity is specifically associated with cortical cholinergic afferents and support the existence of cortical intrinsic cholinergic neurons.

Acetylcholinesterase↗