Domain dissection and characterization of the aminoglycoside resistance enzyme ANT(3″)-Ii/AAC(6')-IId from Serratia marcescens

Aminoglycosides (AGs) are broad-spectrum antibiotics whose constant use and presence in growth environments has led bacteria to develop resistance mechanisms to aid in their survival. A common mechanism of resistance to AGs is their chemical modification (nucleotidylation, phosphorylation, or acetylation) by AG-modifying enzymes (AMEs). Through evolution, fusion of two AME-encoding genes has resulted in bifunctional enzymes with broader spectrum of activity. Serratia marcescens, a human enteropathogen, contains such a bifunctional enzyme, ANT(3″)-Ii/AAC(6')-IId. To gain insight into the role, effect, and importance of the union of ANT(3″)-Ii and AAC(6')-IId in this bifunctional enzyme, we separated the two domains and compared their activity to that of the full-length enzyme. We performed a thorough comparison of the substrate and cosubstrate profiles as well as kinetic characterization of the bifunctional ANT(3″)-Ii/AAC(6')-IId and its individually expressed components.

Biochemical and structural analysis of aminoglycoside acetyltransferase Eis from Anabaena variabilis

The Mycobacterium tuberculosis enhanced intracellular survival (Eis_Mtb) protein is a clinically important aminoglycoside (AG) multi-acetylating enzyme. Eis homologues are found in a variety of mycobacterial and non-mycobacterial species. Variation of the residues lining the AG-binding pocket and positions of the loops bearing these residues in the Eis homologues dictates the substrate specificity and, thus, Eis homologues are Nature-made tools for elucidating principles of AG recognition by Eis. Here, we demonstrate that the Eis from Anabaena variabilis (Eis_Ava), the first non-mycobacterial Eis homologue reported, is a multi-acetylating AG-acetyltransferase. Eis_Ava, Eis from Mycobacterium tuberculosis (Eis_Mtb), and Eis from Mycobacterium smegmatis (Eis_Msm) have different structures of their AG-binding pockets. We perform comparative analysis of these differences and investigate how they dictate the substrate and cosubstrate recognition and acetylation of AGs by Eis.

Aminoglycoside multiacetylating activity of the enhanced intracellular survival protein from Mycobacterium smegmatis and its inhibition

The enhanced intracellular survival (Eis) protein improves the survival of Mycobacterium smegmatis (Msm) in macrophages and functions as the acetyltransferase responsible for kanamycin A resistance, a hallmark of extensively drug-resistant (XDR) tuberculosis, in a large number of Mycobacterium tuberculosis (Mtb) clinical isolates. We recently demonstrated that Eis from Mtb (Eis_Mtb) efficiently multiacetylates a variety of aminoglycoside (AG) antibiotics. Here, to gain insight into the origin of substrate selectivity of AG multiacetylation by Eis, we analyzed AG acetylation by Eis_Msm, investigated its inhibition, and compared these functions to those of Eis_Mtb. Even though for several AGs the multiacetylation properties of Eis_Msm and Eis_Mtb are similar, there are three major differences. (i) Eis_Msm diacetylates apramycin, a conformationally constrained AG, which Eis_Mtb cannot modify. (ii) Eis_Msm triacetylates paromomycin, which can be only diacetylated by Eis_Mtb. (iii) Eis_Msm only monoacetylates hygromycin, a structurally unique AG that is diacetylated by Eis_Mtb. Several nonconserved amino acid residues lining the AG-binding pocket of Eis are likely responsible for these differences between the two Eis homologues. Specifically, we propose that because the AG-binding pocket of Eis_Msm is more open than that of Eis_Mtb, it accommodates apramycin for acetylation in Eis_Msm, but not in Eis_Mtb. We also demonstrate that inhibitors of Eis_Mtb that we recently discovered can inhibit Eis_Msm activity. These observations help define the structural origins of substrate preference among Eis homologues and suggest that Eis_Mtb inhibitors may be applied against all pathogenic mycobacteria to overcome AG resistance caused by Eis upregulation.

Kinase-Catalyzed Biotinylation

Kinase-catalyzed protein phosphorylation plays an essential role in a variety of biological processes. Methods to detect phosphoproteins and phosphopeptides in cellular mixtures will aid in cell biological and signaling research. Our laboratory recently discovered the utility of γ-modified ATP analogues as tools for studying phosphorylation. Specifically, ATP-biotin can be used for labeling and visualizing phosphoproteins from cell lysates. Because the biotin tag is suitable for protein detection, the biotinylation reaction can be applied to multiple phosphoproteomics applications. Herein we report a general protocol for labeling phosphopeptides and phosphoproteins in biological samples using kinase-catalyzed biotinylation.

Dissecting the cosubstrate structure requirements of the Staphylococcus aureus aminoglycoside resistance enzyme ANT(4')

Aminoglycosides are important antibiotics used against a wide range of pathogens. As a mechanism of defense, bacteria have evolved enzymes able to inactivate these drugs by regio-selectively adding a variety of functionalities (acetyl, phospho, and nucelotidyl groups) to their scaffolds. The aminoglycoside nucleotidyltransferase ANT(4') is one of the most prevalent and unique modifying-enzymes. Here, by TLC, HRMS, and colorimetric assays, we demonstrate that the resistance enzyme ANT(4') from Staphylococcus aureus is highly substrate and cosubstrate promiscuous. We show that deoxy-ribonucleotide triphosphates (dNTPs) are better cosubstrates than NTPs. We demonstrate that the position of the triphosphate group (5' and not 3') on the ribose/deoxyribose ring is important for recognition by ANT(4'), and that NTPs with larger substituents at the 3'-position of the ribose ring are not cosubstrates for ANT(4'). We confirm that for all aminoglycosides tested, the respective nucleotidylated products are completely inactive. These results provide valuable insights into the development of strategies to combat the ever-growing bacterial resistance problem.

The future of aminoglycosides: the end or renaissance?

Although aminoglycosides have been used as antibacterials for decades, their use has been hindered by their inherent toxicity and the resistance that has emerged to these compounds. It seems that such issues have relegated a formerly front-line class of antimicrobials to the proverbial back shelf. However, recent advances have demonstrated that novel aminoglycosides have a potential to overcome resistance as well as to be used to treat HIV-1 and even human genetic disorders, with abrogated toxicity. It is not the end for aminoglycosides, but rather, the challenges faced by researchers have led to ingenuity and a change in how we view this class of compounds, a renaissance.

Exploring the substrate promiscuity of drug-modifying enzymes for the chemoenzymatic generation of N-acylated aminoglycosides

Aminoglycosides are broad-spectrum antibiotics commonly used for the treatment of serious bacterial infections. Decades of clinical use have led to the widespread emergence of bacterial resistance to this family of drugs limiting their efficacy in the clinic. Here, we report the development of a methodology that utilizes aminoglycoside acetyltransferases (AACs) and unnatural acyl coenzyme A analogues for the chemoenzymatic generation of N-acylated aminoglycoside analogues. Generation of N-acylated aminoglycosides is followed by a simple qualitative test to assess their potency as potential antibacterials. The studied AACs (AAC(6')-APH(2'') and AAC(3)-IV) show diverse substrate promiscuity towards a variety of aminoglycosides as well as acyl coenzyme A derivatives. The enzymes were also used for the sequential generation of homo- and hetero-di-N-acylated aminoglycosides. Following the clinical success of the N-acylated amikacin and arbekacin, our chemoenzymatic approach offers access to regioselectively N-acylated aminoglycosides in quantities that allow testing of the antibacterial potential of the synthetic analogues making it possible to decide which molecules will be worth synthesizing on a larger scale.

Evidence for changing of cosmic ray composition between 10(17) and 10(18) eV from multicomponent measurements

The average mass composition of cosmic rays with primary energies between 10(17) and 10(18) eV has been studied using a hybrid detector consisting of the High Resolution Fly's Eye (HiRes) prototype and the MIA muon array. Measurements have been made of the change in the depth of shower maximum and the muon density as a function of energy. The results show that the composition is changing from a heavy to lighter mix as the energy increases.

Neurocytoma of the cauda equina. Case report

A case of a neurocytoma involving a nerve root of the cauda equina in a 46-year-old woman is reported. The patient presented with a 2-month history of progressive left lower-extremity weakness and pain and decreased ability to walk, as well as complaints of incomplete voiding. A magnetic resonance image revealed a 7-mm oval mass that was located intrathecally and extended from T-12 to L-1 and was adjacent to a nerve root. No lesions were identified at higher vertebral levels. The mass was excised. On histological examination it was found to have classical features of a neurocytoma. To the best of the authors' knowledge, this is the first report of a neurocytoma occurring in that region. A detailed histological description of this case and review of the pertinent literature are provided.

Selective kallikrein-kinin system activation in inbred rats differentially susceptible to granulomatous enterocolitis

BACKGROUND & AIMS

Crohn's disease is characterized by unrestrained inflammation with a genetic component. Genetic susceptibility and activation of the kalli-krein-kinin (contact) system were investigated in experimental enterocolitis and extraintestinal inflammation induced by bacterial polymers.

METHODS

Kinetics of inflammation in inbred Lewis and Buffalo rats injected subserosally with peptidoglycan-polysaccharide polymers were correlated with in vivo and in vitro activation of the contact system.

RESULTS

Lewis rats had a biphasic course of enterocolitis. Acute inflammation peaked 1 day after injection, gradually decreasing until day 14 when intestinal inflammation spontaneously reactivated and persisted for 16 weeks, accompanied by arthritis, granulomatous hepatitis, anemia, and leukocytosis. Self-limited acute enterocolitis in Buffalo rats resolved by 24 days without extraintestinal involvement. Consumption of the precursor proteins prekalli-krein and high-molecular-weight kininogen indicated activation of the plasma contact system in Lewis rats and closely correlated with chronic intestinal inflammation. Contact system activation did not occur in Buffalo rats, even during acute inflammation. In vitro studies showed a decreased rate of kininogen cleavage in Buffalo plasma.

CONCLUSIONS

Selective in vivo and in vitro activation of the contact system in susceptible Lewis rats suggests that this pathway is one determinant of genetic susceptibility to granulomatous enterocolitis and systemic complications.

Aneurysm of the left middle cerebral artery caused by myxoid degeneration of the vessel wall

BACKGROUND

Myxoid degeneration of arterial walls may result in dissection and dissecting aneurysms in extracranial and intracranial portions of cerebral arteries. Rarely, saccular aneurysms may also develop on that basis, but thus far these have only been reported in the cervical portions of the carotid arteries. We describe a case of a nondissecting aneurysm of the left middle cerebral artery caused by myxoid degeneration of the media.

CASE DESCRIPTION

A 39-year-old man had acute onset of frontal headache and neck stiffness. Computed tomographic scan and lumbar puncture established the presence of subarachnoid hemorrhage. Angiography demonstrated a left middle cerebral artery aneurysm. This was clipped and the wall biopsied. Microscopically the entire thickness of the vascular wall showed marked myxoid alterations. No dissection was present. The patient had an uneventful recovery.

CONCLUSIONS

This observation confirms that myxoid degeneration of arterial walls may cause aneurysms with eventual rupture even in the absence of dissection. Rare cases of this type of aneurysm have been reported to occur in the cervical portions of the carotid arteries, but this is the first reported observation of such changes involving an intracerebral artery.

Brain stem auditory evoked potentials from bone stimulation in dogs

Brain stem auditory evoked potential (BAEP) testing with air-conducted click stimuli can be used to diagnose sensorineural deafness in dogs if conductive deafness can be ruled out. Detection of conductive deafness can be performed by recording BAEP elicited by a vibratory stimulus transducer placed against the skull. Air- and bone-conducted BAEP were compared in dogs, varying bone stimulator placement, click polarity, and stimulus intensity. Optimal bone stimulator placement was determined to be over the mastoid process, followed by the mandible and the zygomatic arch. Condensation polarity clicks gave responses preferable to those elicited by rarefaction or alternating polarity. Bone-conducted BAEP peak latencies were significantly longer than air-conducted latencies after correction of the latencies for the air conduction time accompanying air-conducted stimuli. Significant differences between stimulus modalities were not seen for BAEP peak amplitudes or interpeak latencies. Latency-intensity and amplitude-intensity regressions had similar effects for both modalities: latencies decreased and amplitudes increased as stimulus intensity increased.

Depressive effect of isoflurane anesthesia on motor evoked potentials

The influence of the volatile anesthetic isoflurane (Forane) on motor evoked potentials was examined in rats. To record motor evoked potentials, single-shock electrical stimulation was delivered to the forelimb representation of the motor cortex. This resulted in elicitation of a compound muscle action potential from the contralateral extensor muscles. The effect of isoflurane was examined at various concentrations ranging from 0.2 to 1.5%. With increasing concentrations of isoflurane there was a progressive increase in onset latency of the compound muscle action potential and a decrease in peak-to-peak amplitude and duration. Latencies were significantly increased over baseline values for concentrations of isoflurane from 0.5 to 1.5% (P values were 0.001 to 0.007). For the amplitude and the duration, responses at 0.5 to 1.5% isoflurane were significantly lower than baseline (P values were 0.001 to 0.007). We conclude that isoflurane anesthesia significantly changes the muscle response evoked by motor cortex stimulation in experimental animals.

Suppression of Motor Evoked Potentials by Inhalation Anesthetics

The purpose of this study was to record evoked action potentials from forearm muscles in response to single-shock supramaximal electrical stimulation of motor cortex in room air and under different concentrations (0.5-1.5%) of isoflurane, enflurane, and halothane anesthesia in rats. Anesthesia was induced with a mixture of fentanyl and droperiodol, which was then followed by 10-min inhalation of each gas anesthetic under controlled ventilation. Increasing concentrations of isoflurane (n = 12) caused a progressive increase in onset latency and a decrease in peak-to-peak amplitude and duration. Similar increases in latency and decreases in amplitude and duration occurred under enflurane (n = 10) and halothane (n = 10) anesthesia. The three anesthetics caused a significant latency increase over baseline (room air) values for concentrations from 0.5 to 1.5% (p < 0.01). The amplitude and duration of muscle responses under all three volatile anesthetics at 0.5-1.5% concentrations were significantly lower than baseline (p < 0.01). Isoflurane, enflurane, and halothane anesthesia significantly altered the muscle response evoked by motor cortex stimulation in experimental animals.

Progressive and self-induced relaxation training: their relative effects on subjective and autonomic arousal to fearful stimuli

Compared progressive relaxation training (PRT), self-induced relaxation training (SRT), and a rest quietly (RQ) control condition on measures of tonic physiological arousal and phasic physiological and subjective reactions to fearful stimuli. The Mutilation Anxiety Questionnaire was used to identify 48 male and female participants for the two training assessment sessions. Evaluation of tonic reductions in sympathetic arousal indicated: In session one, PRT and SRT were equivalent; in session two, PRT was superior to SRT. Evaluation of subjective response to fearful stimuli favored PRT/SRT over RQ for low, moderately stressful stimuli; PRT was superior to SRT for the most stressful stimuli. An analysis of reported practice between sessions indicated a negative relationship between practice of relaxation skills and response to stressful tonic physiological arousal and attenuating subjective response to stressful stimuli. The interaction between the cognitive and physiological systems and its implication for therapy are discussed.

Validity of teacher nominations of child behavior problems

The purpose of this study was to examine the validity of teachers' identification of problem children. Ninety-five third-grade children served as subjects. Teachers nominated children as a conduct problem, withdrawal problem, or normal, resulting in 16, 14 and 65 children being assigned to the three groups. Behavioral observation, peer sociometric ratings, and academic achievement scores were collected. The results indicated that conduct problem children differed from normal children on behavioral, sociomeptric, and academic measures, whereas withdrawal children differed from normals on the latter two measures. Conduct problem and withdrawal problem children did not differ on any of the dependent measures. The results suggest that teachers can identify children who are having difficulties in class but may be less accurate in differentiating between different types of problem children.

Effects of a procedure derived from the overcorrection principle on manipulated and nonmanipulated behaviors

Positive practice overcorrection has been shown to be effective in reducing stereotypic self-stimulatory behaviors displayed by retarded and autistic individuals. In addition, the procedure also may increase the occurrence of appropriate behavior through intensive practice. In the present study, several stereotypic and one appropriate behavior (appropriate toy play1 displayed by two autistic children were measured before and during treatment by a positive practice in appropriate toy play overcorrection procedure. Overcorrection was introduced for each of the targeted inappropriate behaviors in sucession for both children. Results showed that overcorrection reduced all stereotypic behaviors displayed by both children. In addition, one subject displayed marked increases in the behavior practiced during overcorrection, appropriate toy play, relative to its baseline rate of occurrence. The results indicate that for some individuals, overcorrection may be effective in teaching and motivating appropriate forms of behavior as well as in reducing stereotypy.