Diffusion and interaction dynamics of the cytosolic peroxisomal import receptor PEX5.

Cellular functions rely on proper actions of organelles such as peroxisomes. These organelles rely on the import of proteins from the cytosol. The peroxisomal import receptor PEX5 takes up target proteins in the cytosol and transports them to the peroxisomal matrix. However, its cytosolic molecular interactions have so far not directly been disclosed. Here, we combined advanced optical microscopy and spectroscopy techniques such as fluorescence correlation spectroscopy and stimulated emission depletion microscopy with biochemical tools to present a detailed characterization of the cytosolic diffusion and interaction dynamics of PEX5. Among other features, we highlight a slow diffusion of PEX5, independent of aggregation or target binding, but associated with cytosolic interaction partners via its N-terminal domain. This sheds new light on the functionality of the receptor in the cytosol as well as highlighting the potential of using complementary microscopy tools to decipher molecular interactions in the cytosol by studying their diffusion dynamics.

Semitubular blade plate for fixation in the proximal humerus.

Rigid internal fixation is frequently difficult to obtain in the proximal humerus, as osteoporotic bone and small fracture fragments may preclude firm purchase of plates and/or screws. We describe our clinical results using a semitubular plate, fashioned into a blade plate device, for fixation of four displaced fractures and three osteotomies of the proximal humerus. All patients were clinically and radiographically united by 4 months postoperatively and had a functional range of motion. The strength of this fixation was compared to that of an AO "T" plate in an oblique subcapital osteotomy model using 10 matched pairs of human humeri. No statistically significant difference could be demonstrated between the two fixation methods with regard to load to failure, yield load, energy absorbed to failure, or stiffness. As a consequence of these studies, we believe the semitubular blade plate expands the options available for challenging fixations in the proximal humerus.