The Hexameric Structures of Human Heat Shock Protein 90

The human 90-kDa heat shock protein (HSP90) functions as a dimeric molecular chaperone. HSP90 identified on the cell surface has been found to play a crucial role in cancer invasion and metastasis, and has become a validated anti-cancer target for drug development. It has been shown to self-assemble into oligomers upon heat shock or divalent cations treatment, but the functional role of the oligomeric states in the chaperone cycle is not fully understood.Here we report the crystal structure of a truncated HSP90 that contains the middle segment and the carboxy-terminal domain, termed MC-HSP90. The structure reveals an architecture with triangular bipyramid geometry, in which the building block of the hexameric assembly is a dimer. In solution, MC-HSP90 exists in three major oligomer states, namely dimer, tetramer and hexamer, which were elucidated by size exclusion chromatography and analytical ultracentrifugation. The newly discovered HSP90 isoform HSP90N that lacks the N-terminal ATPase domain also exhibited similar oligomerization states as did MC-HSP90.While lacking the ATPase domain, both MC-HSP90 and HSP90N can self-assemble into a hexameric structure, spontaneously. The crystal structure of MC-HSP90 reveals that, in addition to the C-terminal dimerization domain, the residue W320 in the M domain plays a critical role in its oligomerization. This study not only demonstrates how the human MC-HSP90 forms a hexamer, but also justifies the similar formation of HSP90N by using 3D modeling analysis

Exploring the Trypanosoma brucei Hsp83 Potential as a Target for Structure Guided Drug Design

Human African trypanosomiasis is a neglected parasitic disease that is fatal if untreated. The current drugs available to eliminate the causative agent Trypanosoma brucei have multiple liabilities, including toxicity, increasing problems due to treatment failure and limited efficacy. There are two approaches to discover novel antimicrobial drugs--whole-cell screening and target-based discovery. In the latter case, there is a need to identify and validate novel drug targets in Trypanosoma parasites. The heat shock proteins (Hsp), while best known as cancer targets with a number of drug candidates in clinical development, are a family of emerging targets for infectious diseases. In this paper, we report the exploration of T. brucei Hsp83--a homolog of human Hsp90--as a drug target using multiple biophysical and biochemical techniques. Our approach included the characterization of the chemical sensitivity of the parasitic chaperone against a library of known Hsp90 inhibitors by means of differential scanning fluorimetry (DSF). Several compounds identified by this screening procedure were further studied using isothermal titration calorimetry (ITC) and X-ray crystallography, as well as tested in parasite growth inhibitions assays. These experiments led us to the identification of a benzamide derivative compound capable of interacting with TbHsp83 more strongly than with its human homologs and structural rationalization of this selectivity. The results highlight the opportunities created by subtle structural differences to develop new series of compounds to selectively target the Trypanosoma brucei chaperone and effectively kill the sleeping sickness parasite

Wstępna analiza możliwości zastosowania spektroskopii fotoakustycznej w fotofizyce gleby

In the present paper, an attempt was made to apply phothoacoustic spectroscopy (PAS) i.e., the particular version of photothermal spectroscopy where a quantity of energy deactivated into heat is evaluated, to quantify photophysical processes in a soil sample. As light sources three diodes emitting at blue, green and red bands of visible light spectrum were used. The obtained dependences of photoacoustic signal amplitude versus light modulation frequency did not follow predictions of Rosencwaig-Gersho classic theory since an additional heat exchange mechanism characteristic of powdered solid samples was likely to occur. In visible light spectrum band, two independent transition processes, achievable to our apparatus, were distinguished. The principal parameters: the relative photoacoustic signal amplitude and characteristic times (1.28 and 0.64 ms) of each revealed process were obtained.W niniejszej pracy podjęto próbę zastosowania spektroskopii fotoakustycznej (PAS), t.j. szczególnej wersji spektroskopii fototermalnej, w której ocenia się ilość energii dezaktywowanej do postaci ciepła, dla ilościowej oceny procesów fotofizycznych zachodzących w próbce glebowej. Jako źródło światła zastosowano trzy diody emitujące w pasmach niebieskim, zielonym i czerwonym widma światła widzialnego. Uzyskane zależności amplitudy sygnału fotoakustycznego od częstotliwości modulacji światła nie były zgodne z przewidywaniami klasycznej teorii Rosencwaiga-Gersho, co mogło być spowodowane wystąpieniem dodatkowego mechanizmu wymiany ciepła, charakterystycznego dla sproszkowanych próbek glebowych. W paśmie widma światła widzialnego wyróżniono dwa niezależne procesy przejściowe, wykrywalne dla naszej aparatury. Otrzymano podstawowe parametry: względną amplitudę sygnału foto-akustycznego oraz czasy charakterystyczne (1,28 oraz 0,64 ms) dla każdego z tych wykrytych procesów

Prognostic significance of augmented metallothionein (MT) expression correlated with Ki-67 antigen expression in selected soft tissue sarcomas

In soft tissue sarcomas, the most important prognostic criteria include extent of malignancy (G), size of the tumour and intensity of Ki-67 antigen expression. In recent times expression of metallothionein (MT) in cells of some malignant processes of epithelial origin was found to correlate with intensity of Ki-67 antigen expression and to carry a possible prognostic significance. The present study aimed at a demonstration of prognostic value of MT expression and at comparing it with Ki-67 antigen expression and G grade in selected soft tissue sarcomas. Immunohistochemical studies were performed on paraffin sections in 54 cases of malignant fibrous histiocytoma (MFH), 18 cases of liposarcoma and 20 cases of synovial sarcoma. The extent of MT and Ki-67 antigen expression was evaluated and an attempt was made to correlate the results with each other and with grade of the tumour. Expression of MT was evident both in the cytoplasm and in cell nuclei of all studied sarcomas. The most pronounced MT expression was noted in MFH-type tumours. The extent of Ki-67 antigen expression was similar in MFH and liposarcoma and was the lowest in synovial sarcoma. In MFH, liposarcoma and synovial sarcoma a pronounced positive correlation was documented between expression of MT and Ki-67 antigen (r=0.85; p<0.001; r=0.93, p<0.0001; r=0.79, p<0.0001). In all types of the tumours a positive relation was detected between MT expression, expression of Ki- 67 and G grade of malignancy in the tumour. Moreover, patients with higher MT expression in the studied tumours demonstrated a shorter survival. MT expression in soft tissue tumours of MFH, liposarcoma and synovial sarcoma type strongly correlated with intensity of proliferation (Ki-67) and G grade and could be useful in defining the extent of malignancy and in prognostic appraisal in the tumours

Improving the detection limit of anion-selective electrodes: an iodide-selective membrane with a nanomolar detection limit

The lower detection limit and the selectivity behavior of anion-selective electrodes (ISEs) are improved by using optimized inner solutions and membrane compositions. With a membrane based on the recently described ionophore [9]mercuracarborand-3, a detection limit of 2 &times; 10-9&nbsp;M has been achieved for iodide. Nevertheless, the improvements are less pronounced than in the case of cation ISEs. This is mainly due to the fact that so far no anion ISE is known with the extremely high selectivities of cation ISEs. If the membrane does not contain an ionophore, leaching of the ion exchanger from the membrane into the sample is also a relevant limiting factor except for ion exchangers of very high lipophilicity.</span