INSIGHTS INTO THE MECHANISM OF RECRUITMENT OF CHECKPOINT PROTEINS BUB1 AND BUBR1 TO KINETOCHORE SITES

Bub1 and BubR1 are essential components of the spindle assembly checkpoint (SAC), a ubiquitous safety mechanism required for accurate segregation of chromosomes during mitosis. Recruitment to mitotic kinetochores, protein assemblies built on the centromeric DNA, might be essential for the functions of Bub1 and BubR1, but the exact recruitment mechanism has been unknown. During my doctoral work, I have tried to investigate this issue at a molecular level. Previously, kinetochore recruitment of Bub1 and BubR1 had been proposed to rely on the interaction of their tetratricopeptide repeats (TPR repeats) with two motifs, named the KI motifs, in the outer kinetochore protein Knl1. In the first part of my doctoral work, I demonstrate that point mutations on the TPR repeats that impair the interaction of Bub1 and BubR1 with Knl1 in vitro and in vivo have essentially no macroscopic effect on the localization of Bub1 and BubR1 at kinetochores. Indeed, we have been able to define a 62-residue segment of Bub1, comprising a motif that mediates the interaction with another checkpoint protein, Bub3, as the minimal kinetochore-binding domain of Bub1. Subsequent studies in other laboratories have identified multiple Met-Glu-Leu-Thr (MELT) motifs in the kinetochore protein Knl1 as crucial docking sites, when phosphorylated by the Mps1 kinase, for the recruitment of Bub1 and BubR1. In the second part of my work, I therefore began to test the hypothesis that Bub1 recognizes MELT repeats on Knl1, through the minimal kinetochore targeting domain and its partner Bub3. Within the context of this new model, I have re-investigated the question whether the KI1 and KI2 motifs have any role in the interaction of Bub1 and BubR1 with Knl1. I provide evidence that Knl11-250 (N-terminal 250 residues of Knl1), with a single MELT motif, drive the assembly of complexes that included all SAC proteins and are sufficient to respond robustly to spindle poisons. Interestingly, I have found that the KI motifs, which flank the MELT motif in Knl11-250, strongly enhance the interaction with SAC components. Conversely, MELT motifs outside of Knl11-250, which lack flanking KI motifs, establish qualitatively similar sets of interactions, but less efficiently. Thus, my analyses indicate that MELT motifs act as independent docking sites for Bub1/Bub3 and assembly stations for SAC signaling complexes, and that KI motifs are MELT enhancers. Collectively, my work has contributed to elucidating important aspects of the molecular mechanism of kinetochore recruitment of two fundamental components of the spindle assembly checkpoint

Sklerodermie und fibrosierende Erkrankungen

Zusammenfassung: Bei der Sklerodermie und anderen fibrosierenden Erkrankungen wie den Fibromatosen, der Arthrofibrose und dem M.Ormond liegt eine Fibroblastenproliferation mit mehr oder weniger starker Begleitentzündung vor. Bei der Sklerodermie kommt es zu einer Hautfibrose mit obstruktiver Vaskulopathie. Sklerodermiforme Hautveränderungen werden auch im Rahmen der "Graft-versus-Host-Disease" nach hämatopoetischer Stammzelltransplantation, bei Malignomen und nach Applikation bestimmter Medikamente beobachtet. Die Fibromatosen werden in eine unter der Hautoberfläche gelegene Gruppe und die tief im Körper lokalisierten Desmoide unterteilt. Im Rahmen des M.Ormond findet sich eine Aortitis mit Ausdehnung der fibrosierenden Entzündung in den Retroperitonealraum. Die Bedeutung der histopathologischen Diagnostik bei fibrosierenden Erkrankungen ist unterschiedlich und reicht von einer erkrankungsbestätigenden bis hin zu einer erkankungsdefinierenden Diagnos

Disordered and Frustrated Magnetization in Coated MnFe₂O₄ Nanoparticles Prepared by Microwave Plasma Synthesis

Disordered and frustrated magnetization of different surface coated (Cr2O3, Co3O4, ZrO2, and SiO2) MnFe2O4 nanoparticles have been studied using SQUID-magnetometry. Magnetic measurements, such as ZFC/FC and ac-susceptibility evidence surface spin-glass behavior. ZFC/FC curves were also compared with numerical simulation to get information about effective anisotropy constants. Frequency dependent ac susceptibility results were analyzed by using Arrhenius, Vogel Fulcher and dynamic scaling laws to further confirm the spin-glass behavior. It is observed that the strength of surface spins disorder and frustration strongly depends upon the type of the coating material. All these analyses signify that disordered and frustrated surface magnetization in MnFe2O4 nanoparticles greatly depend on the type of the surface coating materials and are useful for controlling the nanoparticle’s magnetism for different practical applications

On feasibility of rate-independent stress paths under proportional deformations within hypoplastic constitutive model for granular materials

We study stress paths that are obtained under proportional deformations within the rate-independent hypoplasticity theory of Kolymbas type describing granular materials like soil and broken rock. For a particular simplified hypoplastic constitutive model by Bauer, a closed-form solution of the corresponding system of non-linear ordinary differential equations is available. Since only negative principal stresses are relevant for the granular body, the feasibility of the solution consistent with physics is investigated in dependence of the direction of a proportional strain path and constitutive parameters of the model