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U Hommel

Publications and source records attributed to U Hommel.

8 recordsLinked to original sources
PubMed1992

Human epidermal growth factor. High resolution solution structure and comparison with human transforming growth factor alpha.

The solution structure of the 53 amino acid peptide hormone, human epidermal growth factor (hEGF), has been determined to high resolution from nuclear magnetic resonance (n.m.r.) data. A large number of internuclear distance and dihedral restraints was obtained, including data from uniformly 15N-labelled hEGF. Dynamical simulated annealing methods using the program XPLOR were used for structure calculation. An improved protocol was developed combining efficient conformational searching at a reduced computational cost. The general fold of the calculated structures compared well with that of a derivative of the carboxy-terminally truncated hEGF determined previously. A group of 44 structures were calculated with no violations greater than 0.3 A and 3 degrees for distance and dihedral restraints, respectively. The average pairwise root mean square (r.m.s.) deviation of all backbone atoms for these structures was 2.25 A for all 53 residues, 0.92 A for the bulk of the protein, and 0.23 A for the functionally important carboxy-terminal domain. Two new helical segments containing highly conserved amino acids have been identified; one between cysteines 6 and 14 and a second at the end of the carboxy-terminal domain. New insight into the molecular architecture of the site of putative receptor binding was provided by comparing the structure of hEGF with its biologically equipotent analogue, human transforming growth factor alpha. This comparison revealed a close structural relationship between the two growth factors and provides an improved understanding of the structure/function relationships in EGF.

Amino Acid Sequence↗
PubMed1991

Structure-function relationships in human epidermal growth factor studied by site-directed mutagenesis and 1H NMR.

In order to elucidate the mechanism of interaction between human epidermal growth factor (EGF) and its receptor, selected variants of EGF, differing by single amino acid substitutions, have been made by site-directed mutagenesis. The receptor affinity of these mutants was determined by a receptor binding competition assay, and the effects of the substitution on the structure of the protein were assessed by 1H nuclear magnetic resonance techniques. Various substitutions of Arg-41 resulted in substantial reduction in receptor affinity of EGF whereas change of Tyr-13 did not affect binding to the receptor. The 1H resonances of all nonexchangeable protons of the Tyr-13----Leu, Arg-41----His, and Leu-47----Glu variants were assigned and compared in order to assess the structural integrity of these mutants, which possess very different spectral and biological properties. In the case of the Leu-47----Glu mutant, only minor localized spectral changes were observed, confirming that the tertiary structure of the protein is preserved upon mutation. In contrast, for both the Arg-41----His and Tyr-13----Leu variants, significant and strikingly similar spectra changes were observed for many residues located far away from the mutated residues. This implies that similar structural alterations have taken place in both proteins, an idea further supported by hydrogen-exchange experiments where the exchange rates of hydrogen-bonded amide protons for both the Tyr-13----Leu and the Arg-41----His mutants were found to be about 4 times faster than in the wild-type protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Purification and characterization of yeast anthranilate phosphoribosyltransferase.

Anthranilate phosphoribosyltransferase from Saccharomyces cerevisiae has been purified to homogeneity from an overproducing strain. Analytical ultracentrifugation demonstrated that the enzyme is a dimer of Mr = 83,000 +/- 4,000 (S20.w = 4.7 S). Moreover, as shown by active enzyme sedimentation, the enzyme remains dimeric even at low concentrations. The presence of yeast phosphoribosylanthranilate isomerase in the gradient does not lead to complex formation between the two enzymes as might be expected if phosphoribosyl anthranilate, the very labile product of the anthranilate phosphoribosyltransferase, were channelled to phosphoribosylanthranilate isomerase in vivo. The steady-state-kinetic behaviour of the enzyme suggests that catalysis involves a ternary enzyme-substrate complex, with KANTm = 1.6 microM, and KPRib-PPm = 22.4 microM. The enzyme has been used to generate phosphoribosylanthranilate in situ for kinetic studies of phosphoribosylanthranilate isomerase from Escherichia coli: KPRAm = 5 microM, kcat = 40 s-1.

Aldose-Ketose Isomerases↗
PubMed1989

Correct folding of circularly permuted variants of a beta alpha barrel enzyme in vivo.

An important question in protein folding is whether the natural amino and carboxyl termini and the given order of secondary structure segments are critical to the stability and to the folding pathway of proteins. Here it is shown that two circularly permuted versions of the gene of a single-domain beta alpha barrel enzyme can be expressed in Escherichia coli. The variants are enzymically active and are practically indistinguishable from the original enzyme by several structural and spectroscopic criteria, despite the creation of new termini and the cleavage of a surface loop. This novel genetic approach should be useful for protein folding studies both in vitro and in vivo.

Aldose-Ketose Isomerases↗
PubMed1989

[The validity of parameters in neonatal diagnosis and fetal monitoring of breech deliveries. 1. Neonatal status after breech delivery].

By means of 522 singles in breech presentation the pH of umbilical artery (pH u. a.) and Apgar score in comparison to the mode of delivery, duration of pregnancy and weight of neonates have been analysed. The frequency of deliveries by cesarean section in breech presentation was 28.3%, the rate of preterms in these cases amounts to 14.6% and the perinatal mortality to 42.1%. The average value of pH u.a. after vaginal delivery (7.25) was significantly different to the value after cesarean section (7.28). 25% of the pH-values were below 7.20, 10% below 7.10. Mixed acidoses dominated, metabolic ones after vaginal and abdominal deliveries equalled each other. Vaginal deliveries were frequently followed by respiratory acidoses. In 81% of one-minute-Apgar and in 93% of five-minute-Apgar, the score was above 7. According to our experiences the only determination of the pH u.a. after breech deliveries is not sufficient, because of being at risk for the fetus it demands the measurement of the complete acid-base-status. A critical comparison of these data with the clinical status of the newborn is necessary.

Acidosis↗
PubMed1989

[The validity of parameters in neonatal diagnosis and fetal monitoring of breech deliveries. 2. Problems in fetal monitoring in the breech position--a proposal for a standardized biochemical diagnosis].

By means of 149 fetal microblood samplings (FBA) from the breech in deliveries in breech presentation and by means of 64 cardiotocograms the validity of biochemical parameters and biophysical ones of fetal monitoring will be investigated. It takes an increased number of suspect or pathologic CTG into account in cases of breech presentation. By means of FBA it is possible to exclude or to confirm the supposed acidoses. By this the rate of operations during delivery can be reduced or the operation will be indicated respectively. A normal fetal pH resulting from the general biochemical monitoring does enlarge the obstetricians license when the fetus presents himself in advanced parturition in pelvic floor (hold back of breech during assisted spontaneous delivery). A pH less than 7.15 demands an immediate delivery. A prognosis of fetal outcome by means of FBA and CTG is not possible due to difficulties in calculation of the final stage of breech presentation. The difference between fetal pH measured in pelvic floor and pH in umbilical artery must be kept as small as possible and it might be regarded as criterion of the management of the delivery in breech presentation.

Acidosis↗
PubMed1989

[Detection of an early activation-dependent cell surface antigen on human T-lymphocytes].

The binding properties of a monoclonal antibody to an early activation marker of human lymphocytes are described. The monoclonal antibody BL-Ac/p26 binds to an antigen which is expressed on activated lymphocytes. This antigen is not detectable on resting lymphocytes or other blood cells. The surface radioiodinated antigen of activated T cells isolated by the monoclonal antibody BL-Ac/p26 is separated by SDS-PAGE in a major 26k Da component and a minor band (32 kDa) under reducing conditions. These polypeptide chains form disulphide linked dimers on the cell surface (Mr 55-77 kDa). This 26 kDa antigen is a very early activation marker of T lymphocytes. Human T lymphocytes stimulated by mitogens (PHA, ConA or PWM), anti-TCR/CD3 monoclonal antibodies or allogeneic leucocytes express this 26 kDa antigen after 2-4 hours.

Antibodies, Monoclonal↗