A highly active adipyl-cephalosporin acylase obtained via rational randomization

There is strong interest in creating an enzyme that can deacylate natural cephalosporins such as cephalosporin C in order to efficiently acquire the starting compound for the industrial production of semisynthetic cephalosporin antibiotics. In this study, the active site of the glutaryl acylase from Pseudomonas SY-77 was randomized rationally. Several mutations that were found in previous studies to enhance the activity of the enzyme towards adipyl-7-aminodesacetoxycephalosporanic acid (ADCA) and cephalosporin C have now been combined, and libraries have been made in which random amino acid substitutions at these positions are joined. The mutants were expressed in a leucine-deficient Escherichia coli strain and subjected to growth selection with adipyl-leucine or amino-adipyl-leucine as sole leucine source. The mutants growing on these media were selected and purified, and their hydrolysis activities towards adipyl-7-ADCA and cephalosporin C were tested. Several mutants with highly improved activities towards the desired substrates were found in these rationally randomized libraries. The best mutant was selected from a library of totally randomized residues: 178, 266, and 375. This mutant comprises two mutations, Y178F + F375H, which synergistically improve the catalytic efficiency towards adipyl-7-ADCA 36-fold. The activity of this mutant towards adipyl-7-ADCA is 50% of the activity of the wild-type enzyme towards the preferred substrate glutaryl-7-aminocephalosporanic acid, and therefore the characteristics of this mutant approach those needed for industrial application.     

A new approach to the synthesis of APTRA indicators

We have devised a general synthesis of Mg(2+) indicators which is based on the aminophenol triacetic acid (APTRA) structure. The key step is a palladium-catalyzed coupling reaction of a precursor of the APTRA ligand with a fluorescent group. This strategy resulted in new ratioable fluorescent APTRA indicators and the finding that the fluorescence response of these indicators is different for Mg(2+) and Ca(2+) in some cases. We believe that this represents a generally useful approach for combining fluorophore and chelator functionalities.     

Genetic perturbations of RNA reveal structure-based recognition in protein-RNA interaction

Protein-RNA recognition is an essential foundation of cellular processes, yet much remains unknown about these important interactions. The recognition between aminoacyl-tRNA synthetases and their cognate tRNA substrates is highly specific and essential for cell viability, due to the necessity for accurate translation of the genetic code into protein sequences. We selected an active tRNA that is highly mutated in the recognition nucleotides of the acceptor stem region in the alanine system. The functional properties of this mutant and its secondary derivatives demonstrate that recognition cannot be reduced to isolated structural elements, but rather the amino acid acceptor stem is being recognized as a unit.     

Sleep-related obstructive disordered breathing in cleft palate patients after palatoplasty

Sleep-disordered breathing is frequently associated with children presenting congenital midface defects. Because of structural and functional anomalies in the upper airway, children with cleft palate, especially after surgery, may carry a higher risk of developing sleep-disordered breathing. However, the presence of such sleep-disordered breathing in older cleft palate children has not been emphasized. The aim of this comparative overnight cardiorespiratory sleep study was to evaluate cleft palate patients according to sleep-disordered breathing. A group of 43 cleft palate children (17 girls and 26 boys; mean age, 12.1 +/- 3.8 years) was compared with a control group of 20 randomly selected, noncleft children matched for age, sex, and body mass index. None of the patients suffered from manifest sleep-disordered breathing. Cleft palate patients had a statistically significantly higher respiratory disturbance index and snoring index, but no increased apnea index. The data suggest that cleft palate patients having undergone primary closure of the palate demonstrate microsymptoms of nocturnal upper airway obstruction.     

Successful immunotherapy with matrix metalloproteinase-derived peptides in adjuvant arthritis depends on the timing of peptide administration

We have recently found that matrix metalloproteinases (MMPs) are targets for T-cell and B-cell reactivity in experimental arthritis. In the present article, we investigate whether modulation of MMP-specific T-cell responses could influence the course of adjuvant arthritis (AA). Lewis rats were treated nasally with MMP peptides prior to or after AA induction. Administration of the MMP-10 or the MMP-16 peptide prior to AA induction reduced the arthritic symptoms. In contrast, administration of the MMP-10 peptide after AA induction aggravated the arthritic symptoms. The present study shows the possible usefulness of MMP peptides for immunotherapy. However, a clear understanding of proper timing of peptide administration is crucial for the development of such therapies.     

Can MMTV exploit TLR4?

The recognition of microbial pathogens based on their molecular patterns is essential for host defense. Recently, Toll-like receptors have been shown not only to recognize viruses as well as bacteria and fungi, but also to trigger an efficient immune response. A recent publication proposed that the retrovirus mouse mammary tumor virus exploits the pattern-recognition receptor Toll-like receptor 4 to achieve more efficient infection.     

Isolation of novel tRNA(Ala) mutants by library selection in a tRNA(Ala) knockout strain

The relationship between tRNA structure and function has been widely investigated by site-directed mutagenesis. This method has been a very useful tool to reveal the critical bases in tRNAs that are important for recognition and aminoacylation, but has been limited by the large number of possible base combinations in tRNA molecules. We have devised a new method that uses tRNA knockout cells for selection of functional tRNAs from a mutant tRNA gene library to overcome this limitation. To explore the mechanism of tRNA(Ala) recognition, the bases of the acceptor-stem region were randomized and active mutants were selected in a tRNA(Ala) knockout strain. Mutants of tRNA(Ala) having diverse sequence combinations in the acceptor-stem region and a broad range of functional activity to support knockout cell growth were isolated. The mutant tRNAs selected by the method included molecules containing novel base substitutions as well as extensively altered base combinations that would not be readily generated by rationally designed site-directed mutagenesis. Our results emphasize the importance of the acceptor stem as a structural unit in which some nucleotides may carry more weight than others, but in summation every nucleotide contributes to the interaction with the enzyme.     

Recognition of acceptor-stem structure of tRNA(Asp) by Escherichia coli aspartyl-tRNA synthetase

Protein-RNA recognition between aminoacyl-tRNA synthetases and tRNA is highly specific and essential for cell viability. We investigated the structure-function relationships involved in the interaction of the Escherichia coli tRNA(Asp) acceptor stem with aspartyl-tRNA synthetase. The goal was to isolate functionally active mutants and interpret them in terms of the crystal structure of the synthetase-tRNA(Asp) complex. Mutants were derived from Saccharomyces cerevisiae tRNA(Asp), which is inactive with E. coli aspartyl-tRNA synthetase, allowing a genetic selection of active tRNAs in a tRNA(Asp) knockout strain of E. coli. The mutants were obtained by directed mutagenesis or library selections that targeted the acceptor stem of the yeast tRNA(Asp) gene. The mutants provide a rich source of tRNA(Asp) sequences, which show that the sequence of the acceptor stem can be extensively altered while allowing the tRNA to retain substantial aminoacylation and cell-growth functions. The predominance of tRNA backbone-mediated interactions observed between the synthetase and the acceptor stem of the tRNA in the crystal and the mutability of the acceptor stem suggest that many of the corresponding wild-type bases are replaceable by alternative sequences, so long as they preserve the initial backbone structure of the tRNA. Backbone interactions emerge as an important functional component of the tRNA-synthetase interaction.     

Effects of growth hormone treatment on left ventricular dimensions in children with Noonan's syndrome

OBJECTIVE: To study the effects of long-term growth hormone (GH) treatment on left ventricular (LV) dimensions in children with Noonan's syndrome (NS). METHODS: Echocardiographic measurements of LV dimensions were performed before and during GH treatment in 27 participants (21 boys, 6 girls) in a partly controlled 3-year trial of high-dose GH treatment (0.15 IU/kg/day). Nineteen children had a congenital heart defect, 1 of them had hypertrophic obstructive cardiomyopathy. In the first 3 years, the children were assigned to 1 of 2 groups: group A with discontinuation of GH treatment in the 3rd year, or group B without GH treatment in the 1st year. After the 3rd year, 12 of the 27 children were followed up for 2 additional years to evaluate the long-term effects of GH treatment on the heart. RESULTS: At baseline, LV internal diameters were smaller, while posterior wall thickness were thicker than normal. Over the 1st year, changes in LV dimensions were comparable between the 2 groups. No significant differences were found in LV dimensions between the situation at baseline and after 4 years of GH treatment. CONCLUSION: Long-term high-dose GH treatment does not have clinically significant adverse effects on LV dimensions in children with NS.     

Characterization of terminal NeuNAcalpha2-3Galbeta1-4GlcNAc sequence in lipooligosaccharides of Neisseria meningitidis

Group B and C Neisseria meningitidis are the major cause of meningococcal disease in the United States and in Europe. N . meningitidis lipooligosaccharide (LOS), a major surface antigen, can be divided into 12 immunotypes of which L1 through L8 were found among Group B and C organisms. Groups B and C but not Group A may sialylate their LOSs with N-acetylneuraminic acid (NeuNAc) at the nonreducing end because they synthesize CMP-NeuNAc. Using sialic acid-galactose binding lectins as probes in an ELISA format, six of the eight LOS immunotypes (L2, L3, L4, L5, L7, and L8) in Groups B and C bound specifically to Maackia amurensis leukoagglutinin (MAL), which recognizes NeuNAcalpha2- 3Galbeta1-4GlcNAc/Glc sequence, but not to Sambucus nigra agglutinin, which binds NeuNAcalpha2-6Gal sequence. The combination of SDS-PAGE and MAL-blot analyses revealed that these six LOSs contained only the NeuNAcalpha2-3Galbeta1-4GlcNAc trisaccharide sequence in their 4.1 kDa LOS components, which have a common terminal lacto-N-neotetraose (LNnT, Galbeta1-4GlcNAcbeta1-3Galbeta1-4Glc) structure when nonsialylated as shown by previous studies. The LOS-lectin binding was abolished when the LOSs were treated with Newcastle disease viral neuraminidase which cleaves alpha2-->3 linked sialic acid. Methylation analysis of a representative LOS (L2) confirmed that NeuNAc is 2-->3 linked to Gal. Thus, these LOSs structurally mimic certain glycolipids, i.e., paragloboside (LNnT-ceramide) and sialylparagloboside and some glycoproteins in having LNnT and N-acetyllactosamine sequences, respectively, with or without alpha2-->3 linked NeuNAc. The molecular mimicry of the LOSs may play a role in the pathogenesis of N.meningitidis by assisting the organism to evade host immune defenses in man.