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Biomedical subjects

J Bella

Publications and source records attributed to J Bella.

29 records · Page 2Linked to original sources
PubMed1996

Hydrogen bond geometry in DNA-minor groove binding drug complexes.

The geometry of the hydrogen bonding interaction between DNA and minor-groove binding drugs has been analyzed from a sample of 22 crystal structures of DNA-drug complexes, retrieved from the Nucleic Acid Database. Seventy-seven interactions between the drugs and acceptor groups in the nucleotide bases can be classified as hydrogen bonds. Their geometry departs significantly from linearity since, in most instances, the interactions can be described as three-center or multiple hydrogen bonds. Results also show that there is no preference for hydrogen bonds involving positively charged groups in the drugs. Relationships between hydrogen bond geometry and positioning of the drug along the minor groove are also discussed. The information presented may be useful in the design of new specific minor groove binding drugs.

Anti-Bacterial Agents↗
PubMed1996

Structural characterization and solution properties of an acidic branched (1-->3)-beta-D-glucan from Aureobasidium pullulans.

An acidic exopolysaccharide was isolated from a selected strain of Aureobasidium pullulans. On the basis of spectroscopic and chromatographic techniques, the polymer was identified as a beta-D-glucan containing a main chain of (1-->3)-linked beta-D-glucopy-ranosyl units substituted at the O-6 position by single beta-D-glucopyranosyl side chains. The ratio of units in the main chain to units in the side chain was found to be 1.4:1. The ionic character of this exopolysaccharide is due to the presence of malate residues which are linked to the polymer through ester bonds. The degree of substitution was estimated to be very low (0.05). In aqueous solution no signals are present in the NMR spectra strongly suggesting that the polymer adopts a rigid ordered conformation as further confirmed by rheological data. A solvent-induced conformational transition was observed in DMSO in which NMR spectra with good signal-to-noise ratio were obtained. The solution behaviour of the polymer is similar to that of other branched (1-->3)-beta-D-glucans in spite of both the degree of branching and the substitution with malate groups.

Carbohydrate Conformation↗
PubMed1996

Disrupted collagen architecture in the crystal structure of a triple-helical peptide with a Gly-->Ala substitution.

The crystal structure of the collagen-based peptide (Pro-Hyp-Gly)4-Pro-Hyp-Ala-(Pro-Hyp-Gly)5 has provided for the first time a highly detailed picture of the architectural elements that come into play in the collagen triple helix. The center of the molecule, which harbors a Gly-->Ala substitution, shows subtle conformational changes that result in a local untwisting of the triple helix. The characteristic hydrogen bonding pattern of collagen triple helices is replaced by interstitial water bridges. These effects may be relevant to the diseased states derived from Gly-->X mutations in collagens. The possible implications of this disrupted architecture for collagen assemblies are discussed.

Alanine↗
PubMed1995

Hydration structure of a collagen peptide.

BACKGROUND: The collagen triple helix is a unique protein motif defined by the supercoiling of three polypeptide chains in a polyproline II conformation. It is a major domain of all collagen proteins and is also reported to exist in proteins with host defense function and in several membrane proteins. The triple-helical domain has distinctive properties. Collagen requires a high proportion of the post-translationally modified imino acid 4-hydroxyproline and water to stabilize its conformation and assembly. The crystal structure of a collagen-like peptide determined to 1.85 Angstrum showed that these two features may be related. RESULTS: A detailed analysis of the hydration structure of the collagen-like peptide is presented. The water molecules around the carbonyl and hydroxyprolyl groups show distinctive geometries. There are repetitive patterns of water bridges that link oxygen atoms within a single peptide chain, between different chains and between different triple helices. Overall, the water molecules are organized in a semi-clathrate-like structure that surrounds and interconnects triple helices in the crystal lattice. Hydroxyprolyl groups play a crucial role in the assembly. CONCLUSIONS: The roles of hydroxyproline and hydration are strongly interrelated in the structure of the collagen triple helix. The specific, repetitive water bridges observed in this structure buttress the triple-helical conformation. The extensively ordered hydration structure offers a good model for the interpretation of the experimental results on collagen stability and assembly.

Alanine↗
PubMed1994

Crystal and molecular structure of a collagen-like peptide at 1.9 A resolution.

The structure of a protein triple helix has been determined at 1.9 angstrom resolution by x-ray crystallographic studies of a collagen-like peptide containing a single substitution of the consensus sequence. This peptide adopts a triple-helical structure that confirms the basic features determined from fiber diffraction studies on collagen: supercoiling of polyproline II helices and interchain hydrogen bonding that follows the model II of Rich and Crick. In addition, the structure provides new information concerning the nature of this protein fold. Each triple helix is surrounded by a cylinder of hydration, with an extensive hydrogen bonding network between water molecules and peptide acceptor groups. Hydroxyproline residues have a critical role in this water network. The interaxial spacing of triple helices in the crystal is similar to that in collagen fibrils, and the water networks linking adjacent triple helices in the crystal structure are likely to be present in connective tissues. The breaking of the repeating (X-Y-Gly)n pattern by a Gly-->Ala substitution results in a subtle alteration of the conformation, with a local untwisting of the triple helix. At the substitution site, direct interchain hydrogen bonds are replaced with interstitial water bridges between the peptide groups. Similar conformational changes may occur in Gly-->X mutated collagens responsible for the diseases osteogenesis imperfecta, chondrodysplasias, and Ehlers-Danlos syndrome IV.

Alanine↗
PubMed1992

Crystal structure of a helical oligopeptide model of polyglycine II and of other polyamides: acetyl-(glycyl-beta-alanyl)2-NH propyl.

We synthesized and solved the crystalline structure of the oligopeptide acetyl-(glycyl-beta-alanyl)2-NH propyl. The crystal is formed by layers of helical molecules with the same chirality; however, right-handed layers alternate with left-handed ones. Inside every layer, the packing of helices is pseudohexagonal with hydrogen bonds between neighbor molecules. The structure found affords direct support for the model proposed by Crick and Rich for polyglycine II and also provides an interpretation for the structure of a newly found family of polyamides that do not form sheets as observed in most nylon structures.

Amino Acid Sequence↗
PubMed1990

[Lipid composition of the myometrium during labor].

Lipids represent one of the basic components of each cellular and subcellular membrane of the myometrium and their fluidity has a strong influence upon membrane function. Human myometrium was obtained at cesarean sections. Lipids were separated by one-dimensional thin layer chromatography. The chromatoplates were determined on the densitometer Shimadzu CS 930. Lipid profile of the myometrium was studied before the 37th week of pregnancy, at term without contractile activity, further during at term labor with normal contractile activity and at failure of myometrial contractility. Analysis of the obtained data showed changes in lipid fluidity, namely a decrease before the 37th week of pregnancy and at failure of myometrial contractions during at term labor. The decrease of fluidity was caused by a higher content of total cholesterol and a lower content of total phospholipids in the myometrium.

Female↗
PubMed1990

[Phospholipids in the human myometrium in various stages of contraction before and during labor].

A detailed analysis of the myometrium showed that the physical state of phospholipids--fluidity--depends on the ratio of their individual components and changes in relation to the state of contractile activity. The results indicate that before term of labor changes in the fluidity of myometrial phospholipids as well as increased availability of arachidonic acid for prostaglandin synthesis can induce preterm onset of contractile activity. Possibilities of affecting these mechanisms, which belong to the many potential factors inducing preterm labor, are discussed.

Female↗
PubMed1986

Spectroscopic study of N-nitroso compounds decomposition in presence of DNA bases.

Decomposition kinetics of N-ethyl-N-nitrosourea (ENU) as well as that of N-methyl-N-nitroso-N'-nitroguanidine (MNNG) in water medium was studied by means of differential UV spectroscopy. Rate constants of the first order reaction were evaluated. The influence of DNA bases on decomposition rate of above-mentioned compounds was also estimated. With the help of NMR spectroscopy there were identified several products of decomposition as well as those of interaction of the studied compounds with DNA bases.

Animals↗