Expression, purification, and crystallization of two isozymes of 6-phosphoglucose isomerase of Bacillus stearothermophilus

Two isozymes of 6-phosphoglucose isomerase (phosphoglucose isomerase A & phosphoglucose isomerase B), isolated from Bacillus stearothermophilus, have been overexpressed in Escherichia coli strain DF2145 and purified to homogeneity. Crystals of both isozymes have been obtained by the vapor diffusion method. The crystals of phosphoglucose isomerase A have unit cell dimensions a = b = 132.0 A, c = 183.6 A, and diffract to about 2.8 A resolution. An analysis of the reflection data indicates that the crystal system is hexagonal, space group P6122 or P6522. The crystals of phosphoglucose isomerase B complexed with 6-phosphogluconate belong to the orthorhombic space group I222 (or I212121), with cell dimensions a = 75.1 A, b = 95.7 A, c = 171.5 A, and diffract to a resolution of 2.3 A. These crystals promise to yield more detail for the substrate recognition and higher resolution structures of 6-phosphoglucose isomerase.

The first structure of an aldehyde dehydrogenase reveals novel interactions between NAD and the Rossmann fold

The first structure of an aldehyde dehydrogenase (ALDH) is described at 2.6 A resolution. Each subunit of the dimeric enzyme contains an NAD-binding domain, a catalytic domain and a bridging domain. At the interface of these domains is a 15 A long funnel-shaped passage with a 6 x 12 A opening leading to a putative catalytic pocket. A new mode of NAD binding, which differs substantially from the classic beta-alpha-beta binding mode associated with the 'Rossmann fold', is observed which we term the beta-alpha,beta mode. Sequence comparisons of the class 3 ALDH with other ALDHs indicate a similar polypeptide fold, novel NAD-binding mode and catalytic site for this family. A mechanism for enzymatic specificity and activity is postulated.

Crystal structure of cardiotoxin V from Taiwan cobra venom: pH-dependent conformational change and a novel membrane-binding motif identified in the three-finger loops of P-type cardiotoxin

The crystal structure of cardiotoxin V from Taiwan cobra venom (CTX A5) has been solved at pH 8.5 and refined to an R-factor of 20.7% for 7013 reflections [>2sigma(F)] between 8- and 2.19-A resolution. The refined model shows that CTX A5 exists as a dimer. The assembly consists of 974 non-hydrogen atoms from 124 residues and 73 water molecules. The global monomeric structure is similar to that determined by NMR at pH 3.7, characterized by a core formed by two beta-sheets connected with three-finger loops. However, local conformational differences are detected in two functionally important regions, loops I and II. A disparity between the NMR and X-ray structure of CTX A5 is detected near the tip of loop I and can be attributed to the difference in the protonation state of His4 at different pH, resulting in a reorientation of the His4 imidazole ring. A concerted motion of amino acid side chains located near His4 is detected and possibly contributes to the pH-dependent binding ability of CTX A5 to phospholipid model membranes. The second difference, detected at the tip of loop II, is due to the hydrophobic contact between CTX dimers in the crystal packing and the interaction of water molecules with amino acid residues in the loop II region of the CTX containing Pro31 (P-type CTX). This interaction forces loop II into a more rigid omega shape bridging the main chain at positions 27 and 34, contradictory to the flexible, tapering shape detected by NMR. Thus, a novel continuous hydrophobic column capable of binding to and possibly penetrating the membrane lipid bilayer is formed by the tips of the three-finger loops. In this respect, the X-ray crystal structure of CTX A5 may represent the CTX structure in the membrane-binding mode.

Electromyographic (EMG) study of cold shivering in the chronic spinal dog

Cold shivering in six chronic spinal dogs (T9-10), which became capable of weight-bearing standing and/or walking with their hindlimbs, was studied by electromyography (EMG). In the forequarters, EMG activities in the form of grouping discharges (GD) accompanied by visible tremor (VT) were induced at an ambient temperature of 15 degrees C in all the dogs. In the hindquarters, GD with VT were induced at 3 degrees C in one dog. Although GD with VT were not induced in in the remaining dogs, GD without VT were produced by additional cutaneous stimuli to the hindquarters at 3 degrees C. These stimuli never produced GD in the hindquarters at room temperature. Though the mean frequency of GD in the hindquarters was lower than that in the forequarters, the range of the frequency in the hindquarters was much the same as that in the forequarters. During the experiment, the drop in rectal temperature was less than 0.6 degrees C in all of the dogs. These findings suggest that the chronically isolated spinal cord is responsible for cold shivering, while its excitability to cold exposure is less than that of the spinal cord governed by the supraspinal center.

Fine structures of perikaryal myelin sheaths on statoacoustic ganglion cells in 3-day-old chicks

Perikaryal myelin sheaths on statoacoustic ganglion cells in 3-day-old chicks were studied by electron microscopy. The fixation method with a high-concentrated warm fixative helped in successful demonstrations of perikaryal myelin structures. The sheaths were composed of loose and compact myelin mixed by various arrangements. Twenty-seven percent of perikarya were entirely encircled by compact myelin, 71% were partly wrapped by compact myelin, and 2% were wrapped by just loose myelin. The perikaryal myelin was composed of 3 to 16 layers of loose and compact lamellae, whereas the axonal myelin of 10 to 28 of compact lamellae. Since no unmyelinated perikarya, which are covered by a single layer of Schwann cell cytoplasm, were detected, it is suggested that the perikarya myelination on all the ganglion cells has started before 3 days after hatching.

Inhibitory projection from brachioradialis to biceps brachii motoneurones in human

Neural projection from the brachioradialis to the biceps brachii motoneurones in human was studied using the method of post-stimulus time histogram. Electrical stimulation to the radial branch innervating the brachioradialis produced inhibition in 11 out of 21 biceps motor units. The central delays of the inhibition were 0.7-1.2 ms longer than those of the homonymous facilitation. The inhibition was evoked with the intensity below the motor threshold. Pure cutaneous stimulation provoked no effects on the motor-unit firing. These findings suggest that group I afferents from the brachioradials mediate an oligosynaptic inhibition of the biceps brachii motoneurones.

The crystal structure of glutamine-binding protein from Escherichia coli

The crystal structure of the glutamine-binding protein (GlnBP) from Escherichia coli in a ligand-free "open" conformational state has been determined by isomorphous replacement methods and refined to an R-value of 21.4% at 2.3 A resolution. There are two molecules in the asymmetric unit, related by pseudo 4-fold screw symmetry. The refined model consists of 3587 non-hydrogen atoms from 440 residues (two monomers), and 159 water molecules. The structure has root-mean-square deviations of 0.013 A from "ideal" bond lengths and 1.5 degrees from "ideal" bond angles. The GlnBP molecule has overall dimensions of approximately 60 A x 40 A x 35 A and is made up of two domains (termed large and small), which exhibit a similar supersecondary structure, linked by two antiparallel beta-strands. The small domain contains three alpha-helices and four parallel and one antiparallel beta-strands. The large domain is similar to the small domain but contains two additional alpha-helices and three more short antiparallel beta-strands. A comparison of the secondary structural motifs of GlnBP with those of other periplasmic binding proteins is discussed. A model of the "closed form" GlnBP-Gln complex has been proposed based on the crystal structures of the histidine-binding protein-His complex and "open form" GlnBP. This model has been successfully used as a search model in the crystal structure determination of the "closed form" GlnBP-Gln complex by molecular replacement methods. The model agrees remarkably well with the crystal structure of the Gln-GlnBP complex with root-mean-square deviation of 1.29 A. Our study shows that, at least in our case, it is possible to predict one conformational state of a periplasmic binding protein from another conformational state of the protein. The glutamine-binding pockets of the model and the crystal structure are compared and the modeling technique is described.

Electromyographic (EMG) study of the elbow flexors during supination and pronation of the forearm

Activities of the elbow flexors during supination and pronation of the forearm in a normal human volunteer were studied by an electromyography (EMG). The volunteer performed the movement slowly or quickly holding elbow flexion at various angles with or without a load. The biceps brachii showed an increase and a decrease of EMG activities during supination and pronation, respectively. The brachialis and brachioradialis showed a reduction and an increment of EMG activities accompanied by an increase and a decrease of EMG activities in the biceps brachii, respectively. These findings seem to indicate that reciprocal contractions among the elbow flexors permit the biceps brachii to work for supination without an induction of elbow flexion.

Crystals of glutamine-binding protein in various conformational states

Crystals of glutamine-binding protein (GlnBP) in various conformational states have been obtained. Crystals of the ligand-free "open" state (denoted form B) have unit cell dimensions a = 86.3 A, b = 86.3 A, c = 81.5 A, alpha = beta = gamma = 90 degrees and diffract to about 2.3 A resolution. An analysis of the intensity data using an Requiv plot indicates that the crystal system is orthorhombic, space group P2(1)2(1)2(1). Crystals of the ligand-bound "open" state (form B*) are obtained by soaking form B crystals with glutamine (Gln) and diffract to about 1.9 A. Crystals of the GlnBP-Gln complex in a ligand-bound "closed" state (form C) belong to space group P2(1)2(1)2(1) with a = 62.0 A, b = 65.7 A and c = 121.8 A and diffract to about 2.3 A. Crystals of a selenomethionyl GlnBP (form B') are isomorphous to form B crystals and diffract to about 2.1 A resolution.

A genetic study of retinoblastoma

Eight patients with retinoblastoma (RB) were studied by high resolution chromosome R-banding technique, and the esterase D was quantitatively determined in red blood cells of the patients. Among these patients, 2 showed 13q14 deletion mosaicism, 1 showed a monosomy 13q14.1-q14.2, and the remaining 5 had normal karyotype. Our findings indicated that 1) the RB gene is located at 13q14.1. The result confirmed previous data; 2) 13q deletion is an important event in the development of RB; and 3) esterase D determination is an important diagnostic tool in the detection of 13q deletion, useful for prenatal diagnosis and genetic counselling.

Stress responses in alfalfa (Medicago sativa L.) 11. Molecular cloning and expression of alfalfa isoflavone reductase, a key enzyme of isoflavonoid phytoalexin biosynthesis

The major phytoalexin in alfalfa is the isoflavonoid (-)-medicarpin (or 6aR, 11aR)-medicarpin. Isoflavone reductase (IFR), the penultimate enzyme in medicarpin biosynthesis, is responsible for introducing one of two chiral centers in (-)-medicarpin. We have isolated a 1.18 kb alfalfa cDNA (pIFRalf1) which, when expressed in Escherichia coli, converts 2'-hydroxyformononetin stereospecifically to (3R)-vestitone, as would be predicted for IFR from alfalfa. The calculated molecular weight of the polypeptide (35,400) derived from the 954 bp open reading frame compares favorably to estimated Mrs determined for IFR proteins purified from other legumes. The transcript (1.4 kb) is highly induced in elicited alfalfa cell cultures. The kinetics of induction are consistent with the appearance of IFR activity, the accumulation of medicarpin, and the observed induction of other enzymes in the pathway. Low levels of IFR transcripts were found in healthy plant parts (roots and nodules) which accumulate low levels of a medicarpin glucoside. IFR appears to be encoded by a single gene in alfalfa. The cloning of IFR opens up the possibility of genetic manipulation of phytoalexin biosynthesis in alfalfa by altering isoflavonoid stereochemistry.

Stereoisomerism in plant disease resistance: induction and isolation of the 7,2'-dihydroxy-4',5'-methylenedioxyisoflavone oxidoreductase, an enzyme introducing chirality during synthesis of isoflavonoid phytoalexins in pea (Pisum sativum L)

Treatment of pea seedlings with CuCl2 induced the activity of the enzyme NADPH:7,2'-dihydroxy-4',5'-methylenedioxyisoflavone oxidoreductase (DMIRase) that introduces (+) stereoisomerism in pisatin. DMIRase was purified approximately 7000 fold from CuCl2-treated pea seedlings to apparent homogeneity by a six-step process. The purification sequence included (NH4)2SO4 fractionation, gel filtration on AcA 44, chromatography on DEAE-Bio-Gel,phenyl-Sepharose CL-4B, and Reactive Red 120-agarose, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Gel filtration and denaturing electrophoresis showed that the enzyme consisted of a single polypeptide chain with an Mr of 37,500. The pH optimum of DMIRase was determined to be 7.8. The enzyme showed apparent Michaelis constants of 20 microM for 7,2'-dihydroxy-4',5'-methylenedioxyisoflavone and 58 microM for NADPH. The reaction product of the enzyme, sophorol, gave a distinct negative Cotton effect in the region 300-360 nm, which indicated 3S configuration of the molecule. Antibodies against the enzyme were raised in rabbits and characterized for specificity.

[Genetic study of retinoblastoma]

Eight patients with retinoblastoma were studied by high resolution chromosome R-banding technique, and the EsD was quantitatively determined in red blood cells of the patients. Among these patients, two cases showed 13 q 14 deletion mosaicism, one showed a monosomy 13 q 14.1----q 14.2, and the rest had normal karyotype. The EsD activity was proportional to the number of copies of 13 q 14.1 region present. Our findings indicate that (1) the RB gene is located at 13 q 14.1, a region which is critical in the etiology of retinoblastoma, (2) 13q deletion is an important event in the development of retinoblastoma, and (3) EsD determination is an important diagnostic tool in the detection of 13 q deletion, useful for prenatal diagnosis and genetic counselling, permitting early institution of treatment upon early diagnosis.