The Mechanism of HdeA Unfolding and Chaperone Activation

HdeA is a periplasmic chaperone that is rapidly activated upon shifting the pH to acidic conditions. This activation is thought to involve monomerization of HdeA. There is evidence that monomerization and partial unfolding allow the chaperone to bind to proteins denatured by low pH, thereby protecting them from aggregation. We analyzed the acid-induced unfolding of HdeA using NMR spectroscopy and fluorescence measurements, and obtained experimental evidence suggesting a complex mechanism in HdeA's acid-induced unfolding pathway, as previously postulated from molecular dynamics simulations. Counterintuitively, dissociation constant measurements show a stabilization of the HdeA dimer upon exposure to mildly acidic conditions. We provide experimental evidence that protonation of Glu37, a glutamate residue embedded in a hydrophobic pocket of HdeA, is important in controlling HdeA stabilization and thus the acid activation of this chaperone. Our data also reveal a sharp transition from folded dimer to unfolded monomer between pH3 and pH 2, and suggest the existence of a low-populated, partially folded intermediate that could assist in chaperone activation or function. Overall, this study provides a detailed experimental investigation into the mechanism by which HdeA unfolds and activates.

Preplacement assessments. Impact on injury outcomes

Evaluation of the impact of preplacement assessments is important given the resources companies and occupational health nurses allocate to screening and the ambiguity of the literature about the effectiveness of such assessments. This study examined the effects of preplacement assessments on employee injuries. All individuals screened by an occupational health clinic in the upper Midwest and given work restrictions during a 3 year period were identified as cases (n = 67). Cases were matched with controls without work restrictions (n = 264) on the basis of employer, gender, and job. Age was controlled for statistically. Chi-square analysis, used to test differences in percent distribution of injuries between cases and controls, found no statistically significant differences in musculoskeletal injuries between the groups. Work restrictions recommended as a result of preplacement assessments appear to protect vulnerable workers.

Incidence, prevalence, and variables associated with low back pain in staff nurses

The morbidity, lost work time, and interference with effective work due to low back pain are markedly underestimated when only employee health service data are used. Injured subjects averaged more years of generic, orthopedic, and rehabilitation nursing experience than the non-injured group. Of the studied nurses who experienced work related low back pain within the past 6 months, 78% did not report it to management. More attention should be given to adequate staff availability for shared lifting activities, better design and use of mechanical lifting aids, and further research in how to safely perform tasks from the side of the bed.