Structural mechanism of AadA, a dual-specificity aminoglycoside adenylyltransferase from Salmonella enterica

Streptomycin and spectinomycin are antibiotics that bind to the bacterial ribosome and perturb protein synthesis. The clinically most prevalent bacterial resistance mechanism is their chemical modification by aminoglycoside-modifying enzymes such as aminoglycoside nucleotidyltransferases (ANTs). AadA from Salmonella enterica is an aminoglycoside (3″)(9) adenylyltransferase that O-adenylates position 3″ of streptomycin and position 9 of spectinomycin. We previously reported the apo-AadA structure with a closed active site. To clarify how AadA binds ATP and its two chemically distinct drug substrates, we here report crystal structures of WT AadA complexed with ATP, magnesium, and streptomycin and of an active-site mutant, E87Q, complexed with ATP and streptomycin or the closely related dihydrostreptomycin. These structures revealed that ATP binding induces a conformational change that positions the two domains for drug binding at the interdomain cleft and disclosed the interactions between both domains and the three rings of streptomycin. Spectinomycin docking followed by molecular dynamics simulations suggested that, despite the limited structural similarities with streptomycin, spectinomycin makes similar interactions around the modification site and, in agreement with mutational data, forms critical interactions with fewer residues. Using structure-guided sequence analyses of ANT(3″)(9) enzymes acting on both substrates and ANT(9) enzymes active only on spectinomycin, we identified sequence determinants for activity on each substrate. We experimentally confirmed that Trp-173 and Asp-178 are essential only for streptomycin resistance. Activity assays indicated that Glu-87 is the catalytic base in AadA and that the nonadenylating E87Q mutant can hydrolyze ATP in the presence of streptomycin.

Structural and functional studies of mycobacterial IspD enzymes

A number of pathogens, including the causative agents of tuberculosis and malaria, synthesize isopentenyl diphosphate via the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway rather than the classical mevalonate pathway found in humans. As part of a structure-based drug-discovery program against tuberculosis, IspD, the enzyme that carries out the third step in the MEP pathway, was targeted. Constructs of both the Mycobacterium smegmatis and the Mycobacterium tuberculosis enzymes that were suitable for structural and inhibitor-screening studies were engineered. Two crystal structures of the M. smegmatis enzyme were produced, one in complex with CTP and the other in complex with CMP. In addition, the M. tuberculosis enzyme was crystallized in complex with CTP. Here, the structure determination and crystallographic refinement of these crystal forms and the enzymatic characterization of the M. tuberculosis enzyme construct are reported. A comparison with known IspD structures allowed the definition of the structurally conserved core of the enzyme. It indicates potential flexibility in the enzyme and in particular in areas close to the active site. These well behaved constructs provide tools for future target-based screening of potential inhibitors. The conserved nature of the extended active site suggests that any new inhibitor will potentially exhibit broad-spectrum activity.

Bridging the workforce shortage

Some hospitals and systems have devised innovative ways to fill employee vacancies: they are providing educational opportunities for employees to learn new skills, which makes use of their hospital experience and engenders their loyalty.

What price coverage reform?

Coverage reform in the next few decades is all about making choices, paying close attention to what people really need and want, and giving it to them in smarter, more efficient ways than providers have done in the past.

When you hear that whistle blowing. How trustees can reduce the threat of "qui tam" lawsuits

The number of qui tam--whistle-blower--lawsuits against hospitals has increased 1,500 percent in the last decade--in large part because of the high priority the government attaches to Medicare fraud and abuse. Even suits that never make it to court are financially draining and a blow to an organization's reputation. Here are some tips for protecting your hospital.

The impact of the closing of three Massachusetts public chronic disease hospitals: a multidimensional perspective

The closing of three public chronic disease hospitals in Massachusetts in 1991 as a cost-cutting measure sparked renewed attention to the consequences of relocation. Massachusetts officials faithfully carried out a series of measures to assure that patients would be transferred to facilities providing high quality care and that the relocation process would be highly sensitive to patient needs. A survey of family representatives revealed that both the relocation process and the outcome tended to be perceived positively. Quasi-experimental studies of health and survival outcomes, however, provided less favorable results. On two of three measures of health change, relocation was found to have no effect. However, relocation was found to increase the likelihood of incontinence. For patients at the hospital with the greatest concentration of older patients, relocation lead to heightened mortality rates. Also disappointing for State officials was the fact that the anticipated cost savings were less than anticipated. The findings point to the need for renewed efforts to understand the circumstances when relocation places institutionalized older people at serious risk, more careful cost estimates of the savings to be achieved through proposed cost-saving policy changes, and more carefully formulated policy guidelines for relocation of the institutionalized elderly that balance the risks associated with relocation against other public policy objectives.

Use of a screening instrument in women's health care: detecting relationships among victimization history, psychological distress, and medical complaints

The interactive relationship between psychological distress and physical health is a particularly salient one for women. Routine screening for abuse history and current psychological disturbance is essential in providing comprehensive patient care. The present study examines the utility of a brief screening measure in detecting psychological factors in female patients at a primary care facility. Sixty-nine percent of 108 women screened at a women's health clinic reported a history of trauma and almost half (49%) reported having been sexually harassed. Women presenting to treatment for gynecological problems were more likely to be victims of sexual assault and were more likely to report a history of childhood sexual abuse. In addition, women seeking specialized health care also reported increased rates of stress. Relationships among victimization histories, substance use, and eating disturbances were also found. These data suggest the importance of assessing psychological disturbances and trauma histories as part of a comprehensive medical evaluation.

Balancing formal and informal care: meeting needs in a resource-constrained program

Implications of the presence of informal help for the adequacy of formal home care services are examined in a public program that restricts service authorizations to needs that are not addressed by informal caregivers. Four areas of need were examined: local transportation, shopping, housecleaning, and dressing/bathing. The mixture of formal and informal help varied greatly from one area of need to another. Contrary to expectations, the frequency of informal help tended to be positively associated with the reporting of unmet need. The data suggest that in some areas of need, the reporting of unmet need reflects the view that the demands on informal caregivers are excessive and that additional formal services would provide them with welcome relief.

Physical and chemical injuries of the eyes and eyelids

Ocular trauma is not uncommon. Because the tissues associated with visual function are delicate and remarkably specialized, care of ocular injuries is best left to well-trained specialists. Initial care, however, is often simply common sense. Irrigation of chemical burns, sterile techniques, and procedures that salvage tissue are good general principles.

Aphakic cystoid macular edema. Longterm clinical observations

The incidence of clinically significant cystoid macular edema (CME) following cataract surgery has risen sharply with the widespread utilization of intraocular lenses. To evaluate the factors contributing to the incidence of CME, the senior author has divided 1808 of his own cataract cases into three groups according to procedures used: 1) intracapsular cataract extraction (ICCE) with no lens implantation; 2) ICCE with implantation of an iris-supported lens; and 3) extracapsular cataract extraction (ECCE) with implantation of a posterior chamber lens. The incidence of CME in these three groups was 2%, 9.9%, and 1.2%, respectively. Contributing factors and visual outcome in all three groups are reviewed. It is concluded that many of the problems associated with ICCE and iris-supported lens implantation seem to be eliminated with the ECCE-posterior chamber IOL procedure. However, it is emphasized that careful longterm follow-up is required to determine safety.

Pseudophakic bullous keratopathy

Pseudophakic bullous keratopathy (PBK) is a relatively new disease that is rapidly becoming the prime indication for penetrating keratoplasty. From 1977 thru 1981 we performed 81 corneal transplants on 66 eyes for this condition. In our experience, the incidence of PBK, with iris-supported lenses, is five times greater than aphakic bullous keratopathy (ABK). A series of 800 intracapsular cataract extractions (ICCE) with implantation of iris-supported lenses (1975-1979) were reviewed. Thirty-four patients (4.3%) developed PBK (average two years after surgery). In a series of 3,000 simple ICCEs (1955-1980), 24 patients (0.8%) developed ABK. Etiologic factors, methods of prevention, and the results of penetrating keratoplasty are considered. PBK following ICCE is a serious disease entity, usually of multifactorial origin. Though 88% of the patients have clear grafts, a high incidence of associated posterior segment disease tends to nullify the visual result. Planned extracapsular cataract extraction and posterior chamber lens insertion (1979-1982) has reduced our incidence of PBK to 0.3% (1/300). These results are promising but premature.

Keratophakia. Clinical evaluation

The keratophakia and keratomileusis procedures of Barraquer for the correction of aphakia have not gained acceptance in the United States because of thier inherent complexity and degree of difficulty. To determine the practicality, feasibility, and visual rehabilitation potential of these procedures, 13 secondary keratophakia operations were performed at a 500-bed community hospital between March 1980 and April 1981. The first ten cases are reported to allow 6- to 12-month follow-up. All patients in the series were resistant to contact lenses or were poor candidates for secondary intraocular lens implantation. The anatomic results were excellent. Complications were minimal consisting of surface drying problems in three patients related to the sudden steepening of the cornea or pseudo keratoconus effect. Seven patients achieved 20/30 to 20/40 vision with minimal spectacle correction. The keratophakia procedure of Barraquer shows promise and can be duplicated by experienced corneal surgeons, but is not yet a viable alternative to the use of primary intraocular lenses and continuous wear lenses for the general ophthalmologist.

Pseudophakic cystoid maculopathy: a study of 50 cases

The incidence of clinical cystoid macular edema (CME) in routine cataract surgery is about 2%. Clinically significant pseudophakic maculopathy has a higher incidence and is more severe. Fifty cases of CME following intracapsular cataract extraction and intraocular lens implantation in a series of 821 consecutive cases were reviewed. The overall incidence of pseudophakic cystoid macular edema (PCME) was 6.1%. Several clinical observations were made: (1) Young patients, or those under 65, had a much higher incidence of PCME, approaching 20%; (2) chronic inflammation is responsible for pseudophakic cystoid maculopathy; (3) systemic steroid therapy of CME in the pseudophakic patient was beneficial in 80% of the cases, with a response within ten days; and (4) pseudophakic cystoid maculopathy is almost always recurrent and frequently requires maintenance suppression with daily steroid drops after recovery. Forty-four percent of these patients did not recover better than 20/40 visual acuity, suggesting that CME in the pseudophakic patient is not a benign, self-limited disease.

Particle-free environment for refractive keratoplasty

The refractive keratoplasty techniques of keratomileusis and keratophakia require meticulous care to avoid intralamellar foreign particles. A portable High Efficiency Particular Air Filter Unit has been designed to meet the needs of those surgeons clinically performing this surgery. The unit, combined with amorphic techniques has minimized the clinical problem of particulate matter for the general hospital.

Keratophakia: clinical evaluation

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Reconstructive keratoplasty in the management of conditions leading to corneal destruction

Progressive corneal destruction of varying causes can result in pathologic changes that are incompatible with globe survival. Reconstructive keratoplasty and scleroplasty, in combination with other procedures, can be attempted as an alternative to enucleation, evisceration or spontaneous phthisis bulbi. The results of 50 reconstructive keratoplasties in 36 patients with severe corneal destruction are presented with one- to twenty-two year follow-up. Ninety-nine percent of the eyes were salvaged, 69% have clear grafts, 86% are visually improved and 51% achieved acuity of 20/100 or better.