Dimerization of deoxyribonuclease I, lysozyme and papain. Effects of ionic strength on enzymic activity

A Genetic Screen Reveals Novel Targets to Render Pseudomonas aeruginosa Sensitive to Lysozyme and Cell Wall-Targeting Antibiotics

Pseudomonas aeruginosa is capable of establishing airway infections. Human airway mucus contains a large amount of lysozyme, which hydrolyzes bacterial cell walls. P. aeruginosa, however, is known to be resistant to lysozyme. Here, we performed a genetic screen using a mutant library of PAO1, a prototype P. aeruginosa strain, and identified two mutants (ΔbamB and ΔfabY) that exhibited decrease in survival after lysozyme treatment. The bamB and fabY genes encode an outer membrane assembly protein and a fatty acid synthesis enzyme, respectively. These two mutants displayed retarded growth in the airway mucus secretion (AMS). In addition, these mutants exhibited reduced virulence and compromised survival fitness in two different in vivo infection models. The mutants also showed susceptibility to several antibiotics. Especially, ΔbamB mutant was very sensitive to vancomycin, ampicillin, and ceftazidime that target cell wall synthesis. The ΔfabY displayed compromised membrane integrity. In conclusion, this study uncovered a common aspect of two different P. aeruginosa mutants with pleiotropic phenotypes, and suggests that BamB and FabY could be novel potential drug targets for the treatment of P. aeruginosa infection.

Synthesis of lysozyme-metallacarborane conjugates and the effect of boron cluster modification on protein structure and function

Two complementary methods, "in solution" and "in solid state", for the synthesis of lysozyme modified with metallacarborane (cobalt bis(dicarbollide), Co(C2 B9 H11 )2 (2-) ) were developed. As metallacarborane donors, oxonium adducts of cobalt bis(dicarbollide) and 1,4-dioxane or tetrahydropyran were used. The physicochemical and biochemical properties of the obtained lysozyme-metallacarborane conjugates were studied for changes in secondary and tertiary structure, aggregation behavior, and biological activity. Only minor changes in primary, secondary, and tertiary protein structure were observed, caused by the single substitution of metallacarborane on lysozyme. However, the modification produced significant changes in lysozyme enzymatic activity and a tendency toward time- and temperature-dependent aggregation.

Quantitative turbidimetric assay of enzymatic gram-negative bacteria lysis

In this Technical Note, the quantitative turbidimetric assay for determination of the bacteriolytic activity of enzymes with gram-negative bacteria is proposed. The reactivity of hen white-egg lysozyme toward gram-negative E. coli intact cells was studied. It was found that the highest lysis rate occurred at pH 8.9 in the system containing 0.03 M NaCl. The mechanism of the reaction is discussed and applied for the quantitative evaluation of the reaction rate. The proposed method enables fast, reliable, and reproducible analysis of bacteriolytic activity of lysozyme with gram-negative bacteria.

Staphylococcus aureus sortase A exists as a dimeric protein in vitro

We report the first direct observation of the self-association behavior of the Staphylococcus aureus sortase A (SrtA) transpeptidase. Formation of a SrtA dimer was observed under native conditions by polyacrylamide gel electrophoresis and fast protein liquid chromatography (FPLC). Subsequent peptide mass fingerprinting and protein sequencing experiments confirmed the dimeric form of the SrtA protein. Furthermore, SrtA can be selectively cross-linked both in vitro and in Escherichia coli. Multiple samples of enzyme were subjected to analytical sedimentation equilibrium ultracentrifugation to obtain an apparent Kd for dimer formation of about 55 microM. Finally, enzyme kinetic studies suggested that the dimeric form of SrtA is more active than the monomeric enzyme. Discovery of SrtA dimerization may have significant implications for understanding microbial physiology and developing new antibiotics.

Role of magnesium in the failure of rhDNase therapy in patients with cystic fibrosis

BACKGROUND

In the management of cystic fibrosis (CF), rhDNase-I inhalation is widely used to facilitate the removal of the highly viscous and elastic mucus (often called sputum) from the lungs. However, an important group of CF patients does not benefit from rhDNase-I treatment. A study was undertaken to elucidate the reason for the failure of rhDNase-I in these patients and to evaluate strategies to overcome this.

METHODS

The biochemical properties, physical properties, and degradation by rhDNase-I of sputum obtained from clinical responders and non-responders to rhDNase-I were compared, and the ability of magnesium to reactivate rhDNase-I in DNA solutions and in sputum was investigated. The effect of oral magnesium supplements on magnesium levels in the sputum of patients with CF was also examined.

RESULTS

Sputum from clinical responders was extensively degraded in vitro on incubation with rhDNase-I, while sputum from clinical non-responders was not degraded: the median decrease in sputum elasticity in the two groups was 32% and 5%, respectively. Sputum from clinical responders contained significantly higher concentrations of magnesium than sputum from non-responders (2.0 mM v 1.3 mM; p = 0.020). Sputum that could not be degraded by rhDNase-I became degradable after preincubation with magnesium. The effect of magnesium on rhDNase-I activity was mediated through actin. Oral intake of magnesium enhanced the magnesium concentration in the sputum of CF patients.

CONCLUSION

Increasing the magnesium concentration in sputum by, for example, oral magnesium supplements may be a promising new strategy to overcome the failure of rhDNase-I in patients with CF.

Lysozyme dimerization: Brownian dynamics simulation

The lysozyme dimerization reaction has been studied within the framework of encounter-complex (EC) formation theory using the MacroDox software package. Two types of energetically favorite ECs were determined. In the first of them, active-center amino acids of lysozyme take part in the complex formation or the second molecule blocks accessibility to active center sterically. Epitope amino-acid residues are involved in the complex of type II. The existence of both types of complexes does not contradict experimental data. Dimer-formation rate constants for different kinds of EC were calculated. Increasing the pH from 2.0 to 10.0 decreases the total positive lysozyme charge and eliminates the unfavorable repulsive electrostatic interaction. The rate constant of EC formation is inversely proportional to the protein total charge. The association rate constant was also enhanced by an increase of ionic strength that screened repulsive electrostatic interaction between positively charged proteins.

Storage in the yolk platelets of low MW DNA produced by the regressing follicle cells

The present work was carried out to clarify the nature and origin of the yolk DNA present in vitellogenic oocytes of the lizard Podarcis sicula. Morphological and biochemical evidences indicate that it has an intrafollicular origin, from the apoptotic bodies resulting from follicle cells regression at the end of previtellogenesis. This conclusion is reinforced by the observation that the oocyte membrane, in in vitro experiments, is unpermeable to exogenous DNA. Biochemical evidences reveal that the yolk DNA has a low (200bp) molecular weight and this suggests that it is produced by the endonucleases typically involved in apoptotic DNA laddering. Indeed, immunocytochemical analyses demonstrate that follicle cells contain significant amounts of DNAse I. In immunoblots, carried out during different periods of the ovarian cycle, the enzyme shows a MW of about 33, 66 or 100 kDa thus indicating that its activity in the follicle of Podarcis is modulated by dimerization and/or binding to regulatory factors. Mol. Reprod. Dev. 59: 422-430, 2001.

Oligomerization and phase separation in globular protein solutions

We have chemically crosslinked a globular protein, gamma IIIb-crystallin, to produce a system of well-defined oligomers: monomers, dimers, trimers and a mixture of higher n-mers. Gel electrophoresis, size exclusion chromatography, quasielastic light scattering spectroscopy, and electrospray ionization mass spectrometry were used to characterize the oligomers formed. The liquid-liquid phase separation boundaries of the various oligomers were measured. We find that at a given concentration the phase separation temperature strongly increases with the molecular weight of the oligomers. This phase behavior is very similar to previous findings for gamma II-crystallin, for which oxidation-induced oligomerization is accompanied by an increase in the phase separation temperature. These findings imply that for phase separation, the detailed changes of the surface properties of the proteins are less important than the purely steric effects of oligomerization.

Revisiting the action of bovine ribonuclease A and pancreatic-type ribonucleases on double-stranded RNA

Single-strand-preferring ribonucleases of the pancreatic type, structurally and/or catalytically similar to bovine RNase A but endowed with a higher protein basicity, are able to degrade double-stranded RNA (dsRNA) or DNA:RNA hybrids under standard assay conditions (0.15 M NaCl, 0.015 M sodium citrate, pH 7), where RNase A is inactive. This enzyme too, however, becomes quite active if assay conditions are slightly modified or its basicity is increased (polyspermine-RNase). In the attempt to review these facts, we have analyzed and discussed the role that in the process have the secondary structure of dsRNA as well as other variables whose influence has come to light in addition to that of the basicity of the enzyme protein, i.e., the ionic strength, the presence of carbohydrates on the RNase molecule, and the structure (monomeric or dimeric) of the enzyme. A possible mechanism by which dsRNAs are attacked by pancreatic-type RNases has been proposed.

Human seminal ribonuclease. A tool to check the role of basic charges and glycosylation of a ribonuclease in the action of the enzyme on double-stranded RNA

Human seminal ribonuclease (a basic protein occurring in a glycosylated and in a non-glycosylated form) is very active against double-stranded RNAs (De Prisco, R., Sorrentino, S., Leone, E. and Libonati, M. (1984) Biochim. Biophys. Acta 788, 356-363). The action of the two enzyme forms on single-stranded and double-stranded substrates was studied as a function of pH and ionic strength. Results indicate (1) that glycosylation of the RNAase molecule does not affect enzyme action on single-stranded RNAs, while (2) degradation of double-stranded RNAs is moderately increased by the presence of carbohydrates in the enzyme molecule. Human seminal RNAase shows a marked helix-destabilizing activity on poly(dA-dT) X poly(dA-dT). Under various conditions, this action (1) is definitely stronger than that of bovine RNAase A, and (2) seems to be less dependent on the glycosylation than on the basicity of the enzyme protein. The remarkable activity of human seminal RNAase on double-stranded RNA may, at least partly, be related to the enzyme properties mentioned above.