engleski

Stability studies of selected Helicobacter pylori proteins required for survival

We have performed stability studies for selected Helicobacter pylori proteins required for survival of this bacterium – CrdA and HP1026. These studies are important for the successful protein crystallization outcome and structure determination. H. pylori is an important medical target because of the ability to colonize human stomach and to cause several gastric diseases. H. pylori copper resistance determinant CrdA (HP1326) is required for keeping the concentration of free copper ions below toxic levels. HP1026 is part of one of the heat shock operons controlled under the HspR regulator with an unclear function, putatively classified as a helicase like protein.In case of the HP1026 protein treated with 10 % (v/v) glycerol, good quality of the sample for crystallization studies was confirmed by the SEC (dimeric species) and DLS experiment (PDI < 0.12). Thermofluor assay results showed that incubation of the protein with ATP-gamma-S and ADP strongly affects protein stability by shifting the protein-complex denaturation to higher tm values by +3.52 and +5.18 celsius degrees, respectively. Furthermore, monodispersity of the CrdA protein with and without addition of detergent was evaluated by dynamic light scattering. The solution of the CrdA protein without detergent was heterogeneous and contained species in different oligomeric states and with a high level of aggregation. The polydispersity index for the CrdA sample and CrdA plus n-octyl beta-D-glucoside (nOG) was 0.941 and 0.335, respectively, implying that only the sample treated with detergent could be used for the crystallization purpose, Figure 2. The influence of other detergents like lauryldimethylamine N-oxide (LDAO) and n-dodecyl beta-D-maltoside (DDM) on the dispersity of CrdA was also tested, however they only slightly affected the dispersity profile of CrdA. The stability assay of SUMO-CrdA supplemented with different metal ions on the Tycho NT.6 instrument was carried out showing the stability shift of +8.1 celsius degrees for sample treated with Cu(II) ions.

stability, proteins, DLS, thermal stability assay

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