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H Herrmann

Publications and source records attributed to H Herrmann.

249 records · Page 14Linked to original sources
PubMedDate not supplied

Characterization of disulfide crosslink formation of human vimentin at the dimer, tetramer, and intermediate filament levels.

We have investigated the structural interactions of individual molecules of human vimentin in the soluble state and in filaments. Oxidative crosslinking experiments were conducted with wild-type vimentin aimed at the single cysteine in the helical domain coil 2b, mutated cysteine-free vimentin, and derivatives engineered to carry cysteines in presumed d positions of the heptad amino acid repeats in coils 1a and 2b. We provide conclusive evidence that crosslinking of the cysteine 328 in wild-type vimentin, when in the filamentous or tetrameric forms, occurs outside of the coiled-coil dimer, i.e., between staggered dimer molecules. This occurs despite the close axial register of the dimers and contradicts previous deductions. The extent of crosslinking increases with temperature as well as with the concentration of the crosslinking reagent. We conclude therefore that the cysteines are not in an ideal position for crosslinking but that molecular motion is needed to enhance the reaction. The occurrence of collision complexes, which has been speculated in the literature, does not occur and cannot explain these results. Furthermore, using tailless vimentin with the corresponding mutations, we provide compelling evidence that in type III intermediate filament proteins exchange of individual chains between dimers occurs only if the proteins are incubated in urea at concentrations above 3 M. In 5 M urea, however, the exchange is completed within seconds. The same reaction occurs between human vimentin and mouse desmin at a comparable speed, indicating that both type III intermediate filament proteins have a high affinity for one another at the coiled-coil level.

Amino Acid Sequence↗
PubMedDate not supplied

A dosimetric comparison of conventional vs conformal external beam irradiation of a stented coronary artery utilizing a new fluoroscopic imaging detector system.

UNLABELLED: Purpose. To determine whether conformal external photon beam irradiation may prevent or reduce the rate of restenosis of a stented coronary artery following percutaneous transluminal coronary angioplasty (PTCA). Optimal conformal external beam irradiation with limited cardiac dose requires adequate visualization of the stented vascular segment. With existing image intensifiers, identification of a coronary stent is poorly localized. We propose using an amorphous silicon panel detector to observe the movement of the stent during the cardiac cycle. BACKGROUND: Long-term radiation-induced coronary complications can be minimized by: (a) reducing the radiation field sizes, (b) fractionating the total dose over several days, and (c) applying multiple treatment beams. Localization of the movement of the stent during the cardiac cycle may allow for the design of radiation fields that conform to the stented vessel segment. This scheme may permit gating the radiation beam on or off relative to movement of the stent within or outside the radiation fields, respectively. METHODS: Using a new solid-state amorphous silicon planar detector, with a dynamic range of 12 bits, fluoroscopic images of a Palmaz-Schatz coronary stent were obtained. The stent was centered in a polystyrene phantom 20 cm thick and imaged using a 90-kVp, 3.5-ma, source-detector and source stent distances of 114 and 100 cm, respectively. With the solid-state silicon detector, the stent was identified in a single video frame (1/30 s). This fast image acquisition should allow for mapping the motion of the stent during the cardiac cycle. The stent movement during the cardiac cycle may then be correlated with the QRS complex in the electrocardiogram. CONCLUSIONS: The localization of a coronary stent during the cardiac cycle under fluoroscopy permits delivery of small conformal external radiation fields to treat stented coronary arteries, while minimizing radiation dose to surrounding normal cardiac tissue and vasculature. The best selection of treatment beam angles will be provided by high resolution fluoroscopic images of the stented region obtained from different beam directions. The three-dimensional movement of the stent, indexed in time with the QRS complex, will provide an important measure for gating radiation beams for conformal treatment delivery.

Angioplasty, Balloon, Coronary↗