Biomedical subjects

Sam Li

Publications and source records attributed to Sam Li.

2 recordsLinked to original sources

PubMed2006

Structural role of Sfi1p-centrin filaments in budding yeast spindle pole body duplication.

Centrins are calmodulin-like proteins present in centrosomes and yeast spindle pole bodies (SPBs) and have essential functions in their duplication. The Saccharomyces cerevisiae centrin, Cdc31p, binds Sfi1p on multiple conserved repeats; both proteins localize to the SPB half-bridge, where the new SPB is assembled. The crystal structures of Sfi1p-centrin complexes containing several repeats show Sfi1p as an alpha helix with centrins wrapped around each repeat and similar centrin-centrin contacts between each repeat. Electron microscopy (EM) shadowing of an Sfi1p-centrin complex with 15 Sfi1 repeats and 15 centrins bound showed filaments 60 nm long, compatible with all the Sfi1 repeats as a continuous alpha helix. Immuno-EM localization of the Sfi1p N and C termini showed Sfi1p-centrin filaments spanning the length of the half-bridge with the Sfi1p N terminus at the SPB. This suggests a model for SPB duplication where the half-bridge doubles in length by association of the Sfi1p C termini, thereby providing a new Sfi1p N terminus to initiate SPB assembly.

Binding Sites↗

PubMedDate not supplied

An improved algorithm for anisotropic nonlinear diffusion for denoising cryo-tomograms.

Cryo-electron tomography is an imaging technique with an unique potential for visualizing large complex biological specimens. It ensures preservation of the biological material but the resulting cryotomograms are extremely noisy. Sophisticated denoising techniques are thus essential for allowing the visualization and interpretation of the information contained in the cryotomograms. Here a software tool based on anisotropic nonlinear diffusion is described for filtering cryotomograms. The approach reduces local noise and meanwhile enhances both curvilinear and planar structures. In the program a novel solution of the partial differential equation has been implemented, which allows a reliable estimation of derivatives and, furthermore, reduces computation time and memory requirements. Several criteria have been included to automatically select the optimal stopping time. The behaviour of the denoising approach is tested for visualizing filamentous structures in cryotomograms.

Algorithms↗