Mats Strömqvist

Glycosylation of extracellular superoxide dismutase studied by high-performance liquid chromatography and mass spectrometry

Extracellular superoxide dismutase, EC-SOD, the main superoxide dismutase in biological fluids, is known from its lectin binding to be a glycoprotein. We have characterized the glycosylation of recombinant EC-SOD. A tryptic digest of the protein contained only one glycosylated peptide. This peptide was specifically bound to lectins and stained by periodic acid-Schiff stain. Although appearing very large on size-exclusion chromatography, it was shown to be glycosylated at only one site, asparagine-89, by specific cleavage with glycanases followed by mass spectrometry of the resulting peptide. Based on the binding properties of the peptide to concanavalin A and lentil lectin and the elution profile of N-glycanase-treated glycopeptide on ion-exchange chromatography, the carbohydrate appears to be the complex biantennary type with a core fucose.

Structure of the human β-casein encoding gene

Abstract The entire human β-casein-encoding gene, Bca, was cloned and sequenced. The gene consists of eight exons ranging from 21 to 531 nucleotides (nt) in length and extending over 10466 nt. Exon-2 contains the translational start, the entire signal sequence and the codons for the two first amino acids of the mature protein. This corresponds to the organization found in other species. The translational stop is localized to exon-7. Exon/intron boundaries are in accordance with the AG/GT rule and conform to suggested consensus sequences. Splice junctions are located between coding triplets. In all other species analyzed, Bca has been found to consist of nine exons; however, within intron-2 of the human gene, a sequence omitted from human mRNA, but corresponding to exon-3 of other known Bca genes, was revealed.

The rate of polymerization of rabbit skeletal muscle actin is enhanced by polyethylene glycol

SummaryThe effect of polyethylene glycol on the kinetics of actin polymerization was determined by monitoring the enhancement in the fluorescence of pyrenyl-labelled actin. The polymerization of actin at 15 mM KCl was in addition followed by viscometry and light scattering. All three methods showed that the overall rate of polymerization of actin increased 3-4-fold when the concentration of polyethylene glycol was increased from 0 to 6% (w w−1). A further increase in polyethylene glycol concentration to 10% (w w−1) caused a relatively small contribution to the increase in the rate of polymerization. The enhancement of the overall rate of polymerization by polyethylene glycol was also reflected in a significant decrease in the lag time observed when the time course of polymerization was followed by viscometry and light scattering. The steady-state value of fluorescence enhancement and critical concentration of actin were also influenced by polyethylene glycol and the results showed that the extent of polymerization was increased by an increase in the concentration of polyethylene glycol in solution. The effect of polyethylene glycol on both rate and extent of polymerization persisted at physiological salt concentration (150mm KCl, 2mm MgCl2). Since the rate of elongation was affected only to a small extent by polyethylene glycol, we propose that its main effect is on nucleation.

Carbohydrate specificity of theEscherichia coli P-pilus papG protein is mediated by its N-terminal part

The adherence of pyelonephritic Escherichia coli isolates to mammalian host cells is mediated by the P-pili structures on the bacterial surface. The protein constituting the distal part of the pili structure, papG, interacts with glycan receptors on the host cell. Variation in specificity for different glycoconjugates between the isolates, that may reflect variation in host tropism, has been correlated to three different classes of papG. Truncated variants of the class I, II and III papG adhesins were produced as fusion protein in E. coli and analysed for carbohydrate binding. The results showed that both carbohydrate binding and specificity of the papG adhesin resided in a linear part of the N-terminus of the protein.

Brain spectrin fragments and crosslinks actin filaments

The effect of brain spectrin (fodrin) on actin has been studied using viscometry and fluorimetry. Brain spectrin resembles erythrocyte spectrin tetramer in its action on actin. Both proteins crosslink actin filaments giving rise to a large increase in the viscosity but fluorimetry shows that neither affects actin polymerization significantly. In addition, brain spectrin as well as erythrocyte spectrin fragments preformed actin filaments. Actin filaments incubated in the presence of either of the two proteins incorporate actin monomers at a much higher rate showing that more filament ends are generated.

Effect of spectrin dimer on actin polymerization.

Spectrin dimer is shown to influence the polymerization behaviour of actin. The polymerization of both Mg2+‐ and Ca2+‐actin is regulated by an enhancement in the rate of nucleation and a fragmentation of preformed actin filaments. In addition, spectrin decreases the critical concentration of Ca2+‐actin but not that of Mg2+‐actin. This suggests that the two types of actin may differ in their interaction with spectrin dimer probably due to the different conformations. Band 4.1 elevates the effects of spectrin under non‐equilibrium conditions but its contribution is less at steady state.

Characterization of recombinant human extracellular superoxide dismutase.

Recombinant human extracellular superoxide dismutase produced in chinese hamster ovary cells has been characterized using several chromatographic methods. Peptide mapping confirmed the expected primary structure. The 15 amino acids at the N-terminal end were sequenced and were in accordance with expectations in all positions. The C-terminal amino acids have been confirmed both by amino acid composition studies of a peptide of 42 amino acids and by specific sequential cleavage of the last three C-terminal amino acids with carboxypeptidase A. Both methods demonstrated a full length C-terminus. At physiological ionic strength, the dismutase exists for ca. 25% as octamers or larger polymers, and the amount of polymers increases at lower ionic strength.

Cloning and sequencing of human K-casein cDNA

A cDNA encoding kappa-casein of human milk was cloned and sequenced. The kappa-casein cDNA was isolated from a lambda gt11 library generated from mRNA prepared from a mammary gland biopsy obtained from a lactating woman. The library was screened with polyclonal rabbit antibodies raised against purified native kappa-casein. The obtained nucleotide sequence contained an ORF sufficient to encode the entire amino acid sequence of a kappa-casein precursor protein consisting of 182 amino acids. This includes a tentative signal peptide of 20 amino acids and a processed protein of 162 amino acids.