Lightweight, steel silo for agricultural products - structure and assembly concept

Istotnym problemem przemysłu rolno-spożywczego jest przechowywanie niezbędnych do produkcji surowców i półfabrykatów. Zagadnienie to dotyczy zwłaszcza materiałów sypkich, wrażliwych na zanieczyszczenia środowiska oraz zmiany atmosferyczne. Tradycyjne formy składowania zastępuje się więc magazynowaniem w zbiornikach metalowych, w formie stalowych lub aluminiowych silosów. W różnych ośrodkach badawczych w kraju opracowano szereg rozwiązań, które ze względów konstrukcyjnych można podzielić na dwie grupy: silosy z lejem stożkowym na konstrukcji wsporczej oraz z dnem płaskim. Koncepcja konstrukcji cienkościennego stalowego silosu na zboże inne produkty pochodzenia organicznego, opracowana w Politechnice Lubelskiej ma wiele zalet, jest łatwa w transporcie i montażu.A significant issue in the agricultural and food industry is storing raw materials and semi-products necessary for the production. This issue refers in particular to bulk products, sensitive to environmental pollutions and weather changes. Traditional forms of storage are being replaced with storage in metal tanks being steel or aluminum silos. Various research centers in Poland have developed several solutions that may be divided into two groups for structural reasons: silos with a cone funnel on the supporting structure and the ones with a flat bottom. The con-cept of thin-wall steel silo construction for cereal and other organic products, pre-pared by the Technical University of Lublin, has many advantages and its transpor-tation and assembly are easy

Kinetics of chain motions within a protein-folding intermediate

Small proteins can fold remarkably rapidly, even in μs. What limits their rate of folding? The Engrailed homeodomain is a particularly well-characterized example, which folds ultrafast via an intermediate, I, of solved structure. It is a puzzle that the helix2-turn-helix3 motif of the 3-helix bundle forms in approximately 2 μs, but the final docking of preformed helix1 in I requires approximately 20 μs. Simulation and structural data suggest that nonnative interactions may slow down helix docking. Here we report the direct measurement of chain motions in I by using photoinduced electron transfer fluorescence-quenching correlation spectroscopy (PET-FCS). We use a mutant that traps I at physiological ionic strength but refolds at higher ionic strength. A single Trp in helix3 quenches the fluorescence of an extrinsic label on contact with it. We placed the label along the sequence to probe segmental chain motions. At high ionic strength, we found two relaxations for all probed positions on the 2- and 20-μs time scale, corresponding to the known folding processes, and a 200-ns phase attributable to loop closure kinetics in the unfolded state. At low ionic strength, we found only the 2-μs and 200-ns phase for labels in the helix2-turn-helix3 motif of I, because the native state is not significantly populated. But for labels in helix1 we observed an additional approximately 10-μs phase showing that it was moving slowly, with a rate constant similar to that for overall folding under native conditions. Folding was rate-limited by chain motions on a rough energy surface where nonnative interactions constrain motion

Folding of the Pit1 homeodomain near the speed limit

Current questions in protein folding mechanisms include how fast can a protein fold and are there energy barriers for the folding and unfolding of ultrafast folding proteins? The small 3-helical engrailed homeodomain protein folds in 1.7 μs to form a well-characterized intermediate, which rearranges in 17 μs to native structure. We found that the homologous pituitary-specific transcription factor homeodomain (Pit1) folded in a similar manner, but in two better separated kinetic phases of 2.3 and 46 μs. The greater separation and better fluorescence changes facilitated a detailed kinetic analysis for the ultrafast phase for formation of the intermediate. Its folding rate constant changed little with denaturant concentration or mutation but unfolding was very sensitive to denaturant and energy changes on mutation. The folding rate constant of 3 × 105 s-1 in water decreased with increasing viscosity, and was extrapolated to 4.4 × 105 s-1 at zero viscosity. Thus, the formation of the intermediate was partly rate limited by chain diffusion and partly by an energy barrier to give a very diffuse transition state, which was followed by the formation of structure. Conversely, the unfolding reaction required the near complete disruption of the tertiary structure of the intermediate in a highly cooperative manner, being exquisitely sensitive to individual mutations. The folding is approaching, but has not reached, the downhill-folding scenario of energy landscape theory. Under folding conditions, there is a small energy barrier between the denatured and transition states but a larger barrier between native and transition states

Malleability of folding intermediates in the homeodomain superfamily

Members of the homeodomain superfamily are three-helix bundle proteins whose second and third helices form a helix-turn-helix motif (HTH). Their folding mechanism slides from the ultrafast, three-state framework mechanism for the engrailed homeodomain (EnHD), in which the HTH motif is independently stable, to an apparent two-state nucleation-condensation model for family members with an unstable HTH motif. The folding intermediate of EnHD has nearly native HTH structure, but it is not docked with helix1. The determinant of whether two- or three-state folding was hypothesized to be the stability of the HTH substructure. Here, we describe a detailed Φ-value analysis of the folding of the Pit1 homeodomain, which has similar ultrafast kinetics to that of EnHD. Formation of helix1 was strongly coupled with formation of HTH, which was initially surprising because they are uncoupled in the EnHD folding intermediate. However, we found a key difference between Pit1 and EnHD: The isolated peptide corresponding to the HTH motif in Pit1 was not folded in the absence of H1. Independent molecular dynamics simulations of Pit1 unfolding found an intermediate with H1 misfolded onto the HTH motif. The Pit1 folding pathway is the connection between that of EnHD and the slower folding homeodomains and provides a link in the transition of mechanisms from two- to three-state folding in this superfamily. The malleability of folding intermediates can lead to unstable substructures being stabilized by a variety of nonnative interactions, adding to the continuum of folding mechanisms