Physical characteristics of starch granules and susceptibility to enzymatic degradation

Starch, the most abundant component of the diet, is characterized by its variety as well as the versatility of its derivatives in foods. This paper is an overview of the main physical characteristics of the native starch granule. Three different levels of organization are presented: macromolecular structure, crystalline organization and ultrastructure. Starch consists of amylose and amylopectin. Amylose is an essentially linear polymer composed of alpha-1,4-linked D-anhydroglucose units (AGU); amylopectin is a branched polymer clustering a large amount of short linear chains by the linkage of alpha-1,6-bonds, constituting about 5% of the total glycosidic bonds. In the native starch granules, a large number of the macromolecular chains are organized in crystalline structures. Three forms have been found, the A, B and C patterns. So far only A and B starch crystals have been modelled. There is a variation in the susceptibility of the starch granules to enzymatic digestion. This is explained by variation in the morphology of the granules and their crystalline organization.

Adding years to life: effect of avoidable mortality on life expectancy at birth

STUDY OBJECTIVE

The aim was to determine the number of years that could be gained by preventing avoidable deaths.

DESIGN

The study arose from the concept of avoidable causes of death and life expectancy at birth. Four abbreviated life tables were computed. The first included all causes of death; the second excluded all avoidable causes of death; the third and fourth excluded respectively primary and secondary avoidable causes of death.

SETTING

Mortality and population data were taken from Mortality Statistics Offices in Valencia Region, Spain.

MAIN RESULTS

Life expectancy at birth (LEB) was 75.7 years. After removing all avoidable deaths, LEB increased by 1.74 years. This improvement is attributed to avoidable deaths by primary prevention (1.09 years) and avoidable death by secondary prevention (0.37 year).

CONCLUSIONS

According to these results the greatest improvement in LEB would be gained by primary prevention.

Helical epitope of the group B meningococcal alpha(2-8)-linked sialic acid polysaccharide

The immunological properties of the group B meningococcal alpha(2-8)-linked sialic acid polysaccharide have been rationalized in terms of a model where the random coil nature of the polymer can be described by the presence of local helices. The conformational versatility of the alpha NeuAc(2-8)alpha NeuAc linkage has been explored by NMR studies at 600 MHz in conjunction with potential energy calculations for colominic acid, an alpha(2-8)NeuAc polymer, and the trisaccharide alpha NeuAc(2-8)alpha NeuAc(2-8)beta NeuAc. Potential energy calculations were used to estimate the energetically favorable conformers and to describe the wide range of helices which the polymer can adopt. No unique conformer was found to satisfy all NMR constraints, and only ensemble averaged nuclear Overhauser enhancements could correctly simulate the experimental data. Conformational differences between the polymer and the trisaccharide could be best explained in terms of slight changes in the relative distribution of conformers in solution. Similar helical parameters for the alpha(2-8)NeuAc polymer and poly(A) were proposed as the basis for their cross-reactivity to a monoclonal antibody IgMNOV. The unusual length dependency for binding of oligosaccharide to group B specific antibodies was postulated to arise from the recognition of a high-order local helix with an extended conformation which was not highly populated in solution.

Molecular modelling of acarviosine, the pseudo-disaccharide moiety of acarbose, and other inhibitors of alpha-amylases

Acarbose and its homologs inhibit alpha-D-glucosidases, particularly alpha-amylases. These homologs have the same core, the pseudo-disaccharide acarviosine, linked to various numbers of glucose residues. The conformations of (R)- and (S)-acarviosine have been analysed. The potential energy maps, obtained by molecular mechanics calculations, show that acarviosine is flexible and has several important minima. One low-energy form is close to the shape assumed by the acarviosine moiety when acarbose is adsorbed on the surface of glycogen phosphorylase. Another likely conformation is the same as that inferred from n.m.r. data and HSEA calculations. The results reconcile those conflicting reports. Molecular modelling of other inhibitors of alpha-amylases, such as 4-thiomaltose and moranoline, shows that these pseudo-disaccharides can fill similar volumes of conformational space.

[Multiple codification of the causes of death: from dying "of" to dying "from"]

Multiple-cause mortality data is examined in the Valencian Region. In addition to coding the underlying cause of death (UCD), all causes of death which appeared mentioned on death certificates (MCD) were coded according to preliminary rules established by the Mortality Statistics Office. Specific diseases were selected to explore mortality patterns. The average number of conditions coded per death certificate was 2.7. Two or more conditions on the lowest used line appeared in 33.8% of all medical certificates. Septicaemia, high blood pressure and arteriosclerosis stand out among the conditions more often coded as MCD than coded as UCD. Exploring for mortality patterns a statistical association between coronary heart disease and diabetes emerged (p less than 0.0001). Multiple-cause mortality coding allow to discriminate mortality patterns and show a new magnitude to some specific causes of death.

Molecular modelling of protein-carbohydrate interactions. Docking of monosaccharides in the binding site of concanavalin A

A general procedure is described for addressing the computer simulation of protein-carbohydrate interactions. First, a molecular mechanical force field capable of performing conformational analysis of oligosaccharides has been derived by the addition of new parameters to the Tripos force field; it is also compatible with the simulation of protein. Second, a docking procedure which allows for a systematic exploration of the orientations and positions of a ligand into a protein cavity has been designed. This so-called 'crankshaft' method uses rotations and variations about/of virtual bonds connecting, via dummy atoms, the ligand to the protein binding site. Third, calculation of the relative stability of protein ligand complexes is performed. This strategy has been applied to search for all favourable interactions occurring between a lectin [concanavalin A (ConA)] and methyl alpha-D-mannopyranoside or methyl alpha-D-glucopyranoside. For each monosaccharide, different stable orientations and positions within the binding site can be distinguished. Among them, one corresponds to very favourable interactions, not only in terms of hydrogen bonding, but also in terms of van der Waals interactions. It corresponds precisely to the binding mode of methyl alpha-D-mannopyranoside into ConA as revealed by the 2.9 A resolution of the crystalline complex (Derewenda et al., 1989). Some implications of the present modelling study with respect to the molecular basis of the specificity of the interaction of lectins with various monosaccharides are presented.

Data bank of three-dimensional structures of disaccharides: Part II, N-acetyllactosaminic type N-glycans. Comparison with the crystal structure of a biantennary octasaccharide

Conformational energy maps and descriptions of structures at the local minima are presented for the following fragments found in N-acetyllactosaminic type glycans of N-glycoproteins: GlcNAc beta(1-2)Man, GlcNAc beta(1-4)Man, GlcNAc beta(1-6)Man, Gal beta(1-4)GlcNAc, GlcNAc beta(1-3)Gal, Fuc alpha(1-6)GlcNAc, Fuc alpha(1-3)GlcNAc, Xyl beta(1-2)Man, Gal beta(1-3)GlcNAc and GlcNAc beta(1-6)Gal. These results are the second part of a data bank on glycoprotein moieties; five disaccharides found in oligomannose type N-glycans were analysed earlier (Imberty et al., 1990, Glycoconjugate J 7:27-54). In the present study, three to seven minima are found for each dimer. Conformations of disaccharide fragments found in the crystal structure of the complex of a biantennary octasaccharide with Lathyrus ochrus lectin are plotted on these energy maps. While the observed conformations are at predicted minima, they are not always at the minimum predicted to have the lowest energy. Further, not all observed conformations are stabilized by the exo-anomeric effect. We conclude that these oligosaccharides are highly flexible.

[Intracardiac catheter fragment. Presentation of a clinical case]

This is a case report of a 2 year/5 month old female patient with a venous catheter fragment lodged in her right heart and pulmonary artery. The patient was familiar to us because of her ventricular septum defect and pulmonary hypertension secondary to the heart defect. Routine X-rays showed a fragment of the catheter lodged in the heart. The physical examination showed nothing more in addition to that derived from the ventricular defect. Her records included a clavicular phlebotomy at 2 months when suffering from a severe case of dehydration. The cardiac catheterization done at 16 months confirmed the finding of the fragment, which was extracted transluminally. The intracardiac extraction of the venous catheter and the simultaneous closure of the septal defect comprised the treatment applied.

Structure and solution conformations of a cyclic trisaccharide from high-resolution n.m.r. spectroscopy and molecular modelling

The conformational properties of a cyclic trisaccharide: [O-beta-D-glucopyranosyl-(1----6)]3 1,6"-anhydride nonacetate (C36H48O24, 1) have been established by high-resolution 1H- and 13C-n.m.r. spectroscopy in conjunction with potential-energy and molecular-mechanics calculations. The n.m.r. parameters used were nuclear Overhauser enhancements (n.O.e.) and coupling constants. From theoretical models of the trisaccharide, a statistical-mechanics approach was used to compute an ensemble average-relaxation matrix from which the n.O.e. were calculated. The observed nuclear Overhauser enhancements as measured by n.m.r. spectroscopy may be satisfactorily modelled if averaging over two conformational states is considered. In solution, both conformations of the molecule exhibit three-fold symmetry; the beta-linked glucopyranose rings have the 4C1 conformation. In one conformer, the orientation about the (1----6) linkage is characterized by torsion angles phi = 79.5 degrees, psi = 143.5, and omega = -64.3. For the other conformer, these values are phi = -137.7, psi = 68.2, and omega = 45.6. The existence of such a conformer shows that solution behaviour is not dominated by the stabilizing influence of the exoanomeric effect.

Molecular structure of 3-O-(3,6-anhydro-alpha-D-galactopyranosyl)-beta-D-galactopyranose (neocarrabiose) in the solid state and in solution: an investigation by X-ray crystallography, n.m.r. spectroscopy, and molecular mechanics calculations

The crystal structure of neocarrabiose monohydrate, 3-O-(3,6-anhydro-alpha-D-galactopyranosyl)-beta-D-galactopyranose (C12H20O10.H2O) belongs to the monoclinic space group P2(1), and has a unit cell of dimensions a = 6.351(1), b = 7.675(2), c = 15.096(8) A, and beta = 91.11(1) degree. The reducing unit is in the 4C1 conformation, the non-reducing residue is 1C4, with the 3,6-anhydro bridge in an E conformation, and HO-6 is in a gauche-trans conformation. The orientation about the (1----3) linkage is defined by phi = 94.5 degrees and psi = 141.9 degrees. There is an intramolecular hydrogen bond (O-5'...O-2 = 2.777A). The conformation of the pyranose rings in solution, derived from 3JH.H values, were not significantly different from those in the crystal, but the 3,6-anhydro bridge assumed a half-chair conformation. All these features have been rationalised through molecular modelling and computation of potential energy surfaces.

[Behavior of mortality indicators in small geographic areas: relative standardized mortality ratio and standardized proportional mortality ratio]

One of the most commonly used indicators in mortality studies is the Standardized Mortality Ratio (SMR) being the Relative Standardized Mortality Ratio (RSMR) an indicator of the relative magnitude of the SMR for a specific cause of death. Along with these indicators, which must be calculated by using the population at risk, there is the Standardized Proportional Mortality Ratio (SPMR), an indicator which measures the excess mortality referring to the proportional mortality established for a standard population. This paper reviews the theoretic conditions described in literature as being necessary to establish a probability interval for the RSMR centered on the SPMR as well as the correlations between both indicators and the use of the SPMR as a predictor of the RSMR. The results obtained clearly show how difficult it is for these theoretic conditions to exist. However, they do suggest that the SPMR be used as a predictor of RSMR.

Conformational features of C-glycosyl compounds: crystal structure and molecular modelling of "methyl C-gentiobioside"

The crystal of "methyl C-gentiobioside" (methyl 8,12-anhydro-6,7-dideoxy-D-glycero-D-gulo-alpha-D-gluco-trideca pyranoside) (C14H26O10) is triclinic, space group P1, with a = 1.0181 (6) nm, b = 0.8093 (5) nm, c = 0.5066 (4) nm, alpha = 96.03 (5) degrees, beta = 99.94 (5) degrees, gamma = 90.85 (5) degrees. The two D-glucose residues have the 4C1 conformation. The orientation of the beta-(1----6) linkage is characterized by torsion angles phi = 55.9 degrees, psi = 175.1 degrees, and omega = -63.9 degrees. The orientation of the primary hydroxyl group at the non-reducing residue is gauche-trans (omega' = -53.6 degrees). There is no intramolecular hydrogen bond. Molecules are held together by a network of hydrogen bonds involving all of the hydroxyl groups. This crystal structure is the first experimental characterization of a "C-disaccharide". Unlike methyl gentiobioside, which has a high level of conformational flexibility, the "C-disaccharide" has a restricted flexibility. Each of the low-energy conformers in vacuo has a value of phi centered about 60 degrees, in agreement with the solid state conformation, and the exo-anomeric effect is no longer predominant.

[Avoidable years of life lost ratio: an indicator to identify excess mortality in health areas. Mortality workshop of the Valencia region]

Avoidable mortality has been proposed as an outcome indicator of health services. Until now the Standardized Mortality Ratio (SMR) has been the effect measure most used to detect excesses in avoidable mortality. We propose the use, as a complementary measure, of the Avoidable Years of Life Lost Ratio (AYLLR). We show that for tuberculosis, hypertension and for all avoidable deaths both measures provide complementary information, since in some areas where observed deaths are below the expected number (SMR less than 100) we detect an observed number of years of life lost higher than expected (AYLLR greater than 100), due to the occurrence of these deaths at younger ages. The AYLLR is a standardized effect measure that puts a higher weight to premature deaths.

Modelling studies of solvent effects on the conformational stability of agarobiose and neoagarobiose and their relationship to agarose

The conformational equilibria of the low energy conformers of the repeating units of agarose, i.e. neoagarobiose and agarobiose have been studied theoretically in five solvents. The structure of each individual conformer has been refined by molecular mechanics calculations, from the distinct low-energy regions determined from potential energy surfaces. The stability of the conformers in dilute solution has been evaluated through consideration of the relaxed intramolecular energy including electrostatic, dispersion and cavity terms. For each disaccharide, the calculated abundance of conformers is practically independent of the solvent. Dipole moments and linkage rotation have been calculated for each of the low energy conformers. The calculated molar fractions of the stable conformers were used to model the optical rotation values measured for a single strand of agarose chain in its disordered state, and a satisfactory agreement has been reached (lambda cal = -133 degrees, lambda obs = -145 degrees). For the agarose molecule in the solid state, a left-handed threefold single helix, repeating in 2.85 nm is predicted. Such a helix, which represents the calculated stable conformation for a single strand of agarose, should be considered in descriptions of the molecular basis of sol-gel transition of agarose.

Conformational analysis and molecular modelling of the branching point of amylopectin

The conformational properties of 6(2) alpha-D-glucosylmaltotriose have been studied using energy calculations that include van der Waals interactions, hydrogen bond stabilization, exo-anometric effect and torsional potential contributions. The calculations focused mainly on the conformational properties displayed at the alpha(1----6) linkage within the tetrasaccharide for which the conformational space is reported. The tetrasaccharide molecule was then considered as a model compound of the branching point in amylopectin. From molecular modelling, some basic structural features associated with branching were clearly established. It was found that, among the low energy arrangements, the side chain would fold back onto the main backbone, thereby producing dense three-dimensional structures in which a 'parallel' arrangement is achieved. The branching between two strands of the double helix, as found in the crystalline moiety of A and B starches, was further investigated. It was found that one particular set of conformations about the glycosidic linkages in the two different strands, could result in an arrangement such that strands could be connected through an alpha(1----6) glycosidic linkage, with a minimum of distortion. The three-dimensional features derived from the molecular modelling agree with the physical properties and mode of biogenesis within the starch granule; they are in accord with a 'cluster' type of structure.

Electron crystallography of linear polysaccharides

The present article illustrates how the use of electron diffraction data coupled with realistic molecular modeling can yield to unambiguous structural elucidation of linear polysaccharides in the crystalline state. The series of the original ab initio quantitative crystal structure analyses is presented, along with a description of the methods. Pertinent examples showing the unique ability and utility of electron crystallography to yield new structural insights for biologically interesting macromolecules are given.

The double-helical nature of the crystalline part of A-starch

A new three-dimensional structure of the crystalline part of A-starch is described in which the unit cell contains 12 glucose residues located in two left-handed, parallel-stranded double helices packed in a parallel fashion; four water molecules are located between these helices. Chains are crystallized in a monoclinic lattice with a = 2.124 nm, b = 1.172 nm, c = 1.069 nm and gamma = 123.5 degrees, the c axis being parallel to the helix axis. Systematic absences are consistent with the space group B2. The structure was derived from joint use of electron diffraction of single crystals, X-ray powder patterns decomposed into individual peaks and previously reported X-ray fibre diffraction data after adequate re-indexing. The repeating unit consists of a maltotriose moiety where the glucose residues have the 4C1 pyranose conformation and are alpha(1----4) linked. The conformation of the glycosidic linkage is characterized by torsion angles (phi, psi) which take the values (91.8, -153.2), (85.7, -145.3) and 91.8, -151.3); all the primary hydroxyl groups exist in a gauche-gauche conformation. There are no intramolecular hydrogen bonds. Within the double helix, interstrand stabilization is achieved without any steric conflict and through the occurrence of O(2)...O(6) type hydrogen bonds. The present structure is consistent with both physicochemical and biochemical aspects of the crystalline component of the cereal starch granules.

Antiviral activity of uridine 5'-diphosphate glucose analogues against some enveloped viruses in cell culture

Twenty five analogues of uridine 5'-diphosphate glucose were screened against herpes simplex type 2, vaccinia virus, Sindbis virus and African swine fever virus. After screening, the compound 5'-[[[[(2",3",4",6"-tetra-O-benzoyl-alpha-D- glucopyranosyl)oxi]carbonyl]amino]sulfonyl]uridine (2), the synthesis of which has been reported (Camarasa et al., J. Med. Chem. 28, 40-46, 1985), was selected for further study. This compound showed in vitro activity against all viruses tested. The replication of herpes virus type 2 and African swine fever virus was completely inhibited at 100 micrograms/ml and 150 micrograms/ml respectively; vaccinia virus and Sindbis virus were inhibited to a lesser extent. The compound may inhibit several steps in the viral replication process.