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Biomedical subjects

U Lindberg

Publications and source records attributed to U Lindberg.

At least 55 records · Page 3Linked to original sources
PubMed1992

Structural changes in profilin accompany its binding to phosphatidylinositol, 4,5-bisphosphate.

The effect on the structure of profilin of phosphatidylinositol 4,5-bisphosphate (PIP2) binding was probed by fluorescence and circular dichroism (CD) spectroscopy. Fluorescence of Trp3 and Trp31 of profilin at 292 nm showed a linear decrease in solution emission at 340 nm as PIP2/profilin was increased from 0 to 80:1, apparently due to a static quenching mechanism involving formation of a nonfluorescent PIP2/profilin complex. CD spectra revealed an increase of up to 3.3-fold in the molar ellpticity at 222 nm for profilin as it binds PIP2, as well as changes in the Cotton effect between 250 and 310 nm. These results are consistent with a possible increase in the alpha-helix content of profilin triggered by the binding of PIP2.

Animals↗
PubMed1992

Actin as the generator of tension during muscle contraction.

We propose that the key structural feature in the conversion of chemical free energy into mechanical work by actomyosin is a myosin-induced change in the length of the actin filament. As reported earlier, there is evidence that helical actin filaments can untwist into ribbons having an increased intersubunit repeat. Regular patterns of actomyosin interactions arise when ribbons are aligned with myosin thick filaments, because the repeat distance of the myosin lattice (429 A) is an integral multiple of the subunit repeat in the ribbon (35.7 A). This commensurability property of the actomyosin lattice leads to a simple mechanism for controlling the sequence of events in chemical-mechanical transduction. A role for tropomyosin in transmitting the forces developed by actomyosin is proposed. In this paper, we describe how these transduction principles provide the basis for a theory of muscle contraction.

Actins↗
PubMed1991

Actin in ribbons.

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Actin Cytoskeleton↗
PubMed1991

Crystallization and preliminary X-ray analysis of Gc, the vitamin D-binding protein in serum.

The vitamin D-binding protein, Gc, was purified from human serum and crystallized using the hanging-drop method. The best crystals were grown from 28% polyethylene glycol 400 in 50 mM-sodium acetate at pH 4.8. These crystals diffract to 3.4 A and the observed diffraction is consistent with orthorhombic space groups P4(1) and P4(3). The unit cell parameters were determined to be a = b = 135.5 A and c = 75.6 A.

Chromatography, Ion Exchange↗
PubMed1991

Actin depolymerization in the cyclic AMP-stimulated toad bladder epithelial cell, determined by the DNAse method.

Previous studies with the rhodamine phalloidin binding assay have shown that antidiuretic hormone and 8-Br-cAMP rapidly depolymerize F-actin in toad bladder epithelial cells. We have extended these studies with the DNAse inhibition assay and have found that in isolated epithelial cell suspensions, G-actin increases from 37 to 56% of total actin following 8-br-cAMP stimulation. The G-actin concentration in the epithelial cell greatly exceeds its critical concentration, indicating the requirement for a G-actin sequestering protein or proteins in this system.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1990

Polyphosphoinositide synthesis in platelets stimulated with low concentrations of thrombin is enhanced before the activation of phospholipase C.

When platelets, prelabelled with [32P]orthophosphate, were stimulated with thrombin (0.5 U.ml-1) there was an immediate increase in the radioactivity associated with the pools of polyphosphoinositides. Only subsequent to this increase, did the radioactivity of these phospholipid pools decrease as expected from a receptor-mediated activation of phospholipase C (phosphoinositidase). Phosphorylation of diacylglycerol (one of the second messengers formed in the hydrolysis of phosphatidylinositol-bisphosphate) to phosphatidic acid took place with a lag phase of about 3-5 s. Together these experiments suggest that stimulation of kinases phosphorylating phosphatidylinositol and phosphatidylinositol-phosphate may precede or occur in parallel with activation of receptor-linked phosphoinositidase.

Blood Platelets↗
PubMed1989

Molecular packing in profilin: actin crystals and its implications.

Analysis of profilin: actin crystals reveals an extensive intermolecular network, rather than a discrete "monomeric complex", comprising stacked actin ribbons held in place by columns of profilin molecules, wedged in between neighboring actin subunits and running perpendicular to the ribbons. Comparison with data from electron microscopy, X-ray diffraction, spectroscopy, and biochemistry of actin suggests that a simple transformation relates the ribbon to f-actin. The crystals exhibit unusual polymorphic properties, which strengthens the view that movements within the actin monomer are important for force generation.

Actins↗
PubMed1989

Childhood asthma in a rural county.

As part of a questionnaire study of allergic diseases in Swedish children, information about asthma reported in a rural county was evaluated. Of a total population of approx. 9,000 children 4, 7, 10 and 14 years of age, 5.1% reported a history of asthma and 2.4% reported symptoms during the last year. The incidence was highest during the first 2 years of life. A higher incidence in boys than in girls was found only during the first 4 years of life. Cessation of symptoms was most common in children with onset during the first 2 years of life. By checking the medical case records, a high accuracy of the reported information was confirmed.

Adolescent↗
PubMed1989

Allergic diseases in Swedish school children.

The occurrence of allergic diseases in children was studied on the basis of a questionnaire sent to the parents of 20,000 school children, 7, 10 and 14 years of age, in 3 parts of Sweden with different climatic conditions. The prevalence of asthma was 2.4%, allergic rhinoconjunctivitis 7.4%, eczema 7.8% and total allergic diseases 16.9%. The prevalence of all diseases was significantly higher in the northern part of the country than in the southern parts. This geographic variation was not related to heredity, infant feeding pattern or known exposure variables other than the cold and dry climate. Parental history of allergic diseases increased the incidence in the offspring 2-9 times, with a pattern of symptom specificity and a cumulative effect of double parental history. Breast-feeding postponed the onset of allergic disease only in children with double parental history.

Adolescent↗
PubMed1988

The use of poly(L-proline)-Sepharose in the isolation of profilin and profilactin complexes.

In the purification of proline hydroxylase by affinity chromatography on poly(L-proline)-Sepharose it was found earlier that two other components, profilin and the complex profilin-actin, also bind with high affinity to this matrix. We have exploited this observation to develop a rapid procedure for the isolation of profilin and profilin-actin complexes in high yields directly from high-speed supernatants of crude tissue-extracts. Through an extensive search for elution conditions, avoiding poly(L-proline) as the desorbant, we have found that active proteins can be recovered from the affinity column with a buffer containing 30% dimethyl sulphoxide. Subsequent chromatography on hydroxylapatite separates free profilin and the two isoforms of profilactin, profilin-actin beta and profilin-actin gamma. The profilin-actin complexes produced this way have high specific activities in the DNAase-inhibition assay, give rise to filaments on addition of Mg2+, and can be crystallized. From the isolated profilin-actin complexes the beta- and gamma-actin isoforms of non-muscle cells can easily be prepared in a polymerization competent form. Pure profilin is either obtained from an excess pool present in some extracts or by dissociation of profilin-actin complexes and removal of the actin.

Actins↗
PubMed1988

The effect of divalent cations on the interaction between calf spleen profilin and different actins.

The interaction between calf spleen profilin and actin depends critically on the status of the C-terminus of the actin, and in the case of profilin, the C-terminus is of great importance for the physiochemical behaviour of the protein. Both proteins easily lose their C-terminal amino acids during the preparation, and special care has to be taken to ensure the isolation of the proteins in the intact form. Another factor that may seriously influence the study of the interaction of profilin with actin is the presence of varying amounts of an activity that causes an apparent stabilization of the complex even at later stages of its purification. We have found conditions for the isolation of intact profilin and actin, and studied the interaction between the two proteins, including the determination of the Kdiss for the complex formed under various ionic conditions. The complex formed between profilin and actin from calf spleen was found to be significantly stronger (Kdiss less than or equal to 10(-8) M in 50 mM KCl, and Kdiss = 4.10(-7) M in 50 mM KCl, 1 mM MgCl2) than that formed between profilin and muscle alpha-actin (Kdiss = 10(-6) M in 50 mM KCl, +/- 1 mM MgCl2). The profilactin complex formed in the mammalian system was stronger than the complex formed between Acanthamoeba actin and the profilin-like protein isolated from this organism. Analysis of the formation of the calf spleen complex in the presence of varying concentrations of divalent cations gave evidence for the presence of a high-affinity divalent-cation-binding site on the spleen actin (beta, gamma) which appears to regulate the interaction with profilin.

Actins↗
PubMed1988

The primary structure of human platelet profilin: reinvestigation of the calf spleen profilin sequence.

The primary structure of human platelet profilin was determined by aligning the sequences of its tryptic peptides to the previously determined calf spleen profilin sequence [(1979) FEBS Lett. 101, 161-165]. Comparison of the peptide fingerprints of the two proteins suggested a higher homology than that found by direct sequence comparison. We therefore reinvestigated the sequences of the peptides from calf spleen profilin. We identified four incorrect charge assignments and a deletion of three residues. The similarity between the two vertebrate profilins amounts to 95%.

Amino Acid Sequence↗
PubMed1988

Protein kinase C-dependent phosphorylation of profilin is specifically stimulated by phosphatidylinositol bisphosphate (PIP2).

Calf spleen profilin is shown to be an in vitro substrate of purified human placental protein kinase C (PKC), with an apparent Km of 4 microM. Phosphatidylinositol bisphosphate (PIP2) was an effective activator of the profilin phosphorylation by PKC and caused a maximum 13-fold increase of Vmax with a half maximal effect at 40 micrograms/ml. The action of PIP2 was not mimicked by phosphatidylserine, phosphatidic acid or phosphatidylinositol, whereas phosphatidylinositol monophosphate was slightly stimulatory. By contrast, protein kinase C-dependent phosphorylation of histone type III-S, myelin basic protein or lipocortin-I was not affected by PIP. It is suggested that PIP2 modifies the nature of the profilin-PKC interactions.

Amino Acids↗