Processive behaviour of kinesin observed using micro-fabricated cantilevers

The mechanical characterization of biomolecular motors requires force sensors with sub-piconewton resolution. The coupling of a nanoscale motor to this type of microscale sensors introduces structural deformations in the motor according to the thermally activated degrees of freedom of the sensor. At present, no simple solution is available to reduce these effects. Here, we exploit the advantages of micro-fabricated cantilevers to produce a force sensor with essentially one degree of freedom and a spring constant of 0.03 pN nm(-1) for the study of the molecular motor protein kinesin-1. During processive runs, the cantilever constrains the movement of the cargo binding domain of kinesin in a straight line, parallel to the microtubule track, and excludes specific reaction coordinates such as cargo rotation. In these conditions, we measured a step size of 8.0 ± 0.4 nm and a maximal unloaded velocity of 820 ± 80 nm s(-1) at saturated adenosine triphosphate (ATP) concentration. We concluded that the motor does not need to rotate its tail as it moves through consecutive stepping cycles.

[Discrepancies between diagnosed asthma, asthma-like symptoms and a test for abnormal lung function]

For the diagnosis of asthma, it is neither clear to which degree various tests and symptoms identify the same subjects nor how these characteristics are best combined. We assessed the interrelationship between physician-diagnosed asthma, asthma-like symptoms and abnormal airway function in a population based sample of 495 12-15 year old schoolchildren. Participants filled in a questionnaire and underwent baseline spirometry (FEV1%), provocation with treadmill exercise (EXE) and with inhaled methacholine (PD15), and monitoring of peak expiratory flow (PEF) twice daily for two weeks. Most symptomatic subjects with any test positive were identified by PD15 alone (75%) or in combination with PEF monitoring (89%). Although interest agreement was weak (kappa < 0.40 for all pairs), significant associations were found between PD15 and EXE, between PEF and EXE and between FEV1% and PD15. However, PEF variability and methacholine responsiveness seem to identify different varieties of airway pathophysiology, and the combined use of the two tests may be helpful as an epidemiological screening tool for asthma.

[Intercostal neurinoma as a cause of recurrent chest pain]

A case history of an intercostal neurilemmoma as a cause of recurrent chest pain in a young asthma patient is presented. The pathophysiology of the neurilemmoma is summarized and its role in the differential diagnosis of chest pain is shortly discussed.

Spirometry in healthy adult never-smokers

Spirometry was performed in 277 female and 240 male subjects constituting a random, unbiased population sample representative for the population of Denmark. Equipment, calibration and measurement procedures conformed strictly with established standards. Statistical analysis showed that certain power transformations (cubic, quadratic or square root) of the data produced models that fitted the data statistically significantly better than linear models, where no transformations are applied, or logarithmic models where a logarithmic transformation is applied to the response variable. Differences between predictions obtained with the three models were, however, small and without practical significance. Neither rigid adherence to established, well documented standards nor elaborate statistical analysis reduced the inter-individual variance significantly in comparison to previous investigations. The results emphasize that it is important that reference values are appropriate for the methods and populations in question.