Why small proteins tend to have high denaturation temperatures

Some Clues about Enzymes from Psychrophilic Microorganisms

Enzymes purified from psychrophilic microorganisms prove to be efficient catalysts at low temperatures and possess a great potential for biotechnological applications. The low-temperature catalytic activity has to come from specific structural fluctuations involving the active site region, however, the relationship between protein conformational stability and enzymatic activity is subtle. We provide a survey of the thermodynamic stability of globular proteins and their rationalization grounded in a theoretical approach devised by one of us. Furthermore, we provide a link between marginal conformational stability and protein flexibility grounded in the harmonic approximation of the vibrational degrees of freedom, emphasizing the occurrence of long-wavelength and excited vibrations in all globular proteins. Finally, we offer a close view of three enzymes: chloride-dependent α-amylase, citrate synthase, and β-galactosidase.

Hydrolysis kinetics for solubilizing waste activated sludge at low temperature thermal treatment derived from multivariate non-linear model

Low temperature thermal pre-treatment is a low-cost method to break down the structure of extracellular polymeric substances in waste activated sludge (WAS) while improving the sludge biodegradability. However, previous models on low temperature thermal pre-treatment did not adequately elucidate the behaviour of sludge hydrolysis process for the duration ranging from 5 to 9 h. Therefore, this work had developed an inclusive functional model to describe the kinetics of sludge hydrolysis for a wide range of treatment conditions (30 °C-90 °C within 0 and 16 h). As compared with treatment duration, the treatment temperature played a greater impact in solubilizing WAS. Accordingly, the 90 °C treatment had consistently produced WAS with the highest degree of solubility. Nonetheless, the mediocre discrepancies between 90 °C and 75 °C may challenge the practicality of increasing the treatment temperatures beyond 75 °C. The effects of treatment duration on soluble chemical oxygen demand, soluble carbohydrate and soluble protein were only significant during the first 4 h, except for humic substances release that continued to increase with treatment duration. Finally, a good fit with R2 > 0.95 was achieved using an inclusive multivariate non-linear model, substantiating the functionality to predict the kinetics of sludge hydrolysis at arbitrary treatment conditions.

The crystal structure of the domain-swapped dimer of onconase highlights some catalytic and antitumor activity features of the enzyme

Onconase (ONC) is a monomeric amphibian "pancreatic-type" RNase endowed with remarkable anticancer activity. ONC spontaneously forms traces of a dimer (ONC-D) in solution, while larger amounts can be formed when ONC is lyophilized from mildly acidic solutions. Here, we report the crystal structure of ONC-D and analyze its catalytic and antitumor activities in comparison to ONC. ONC-D forms via the three-dimensional swapping of the N-terminal α-helix between two monomers, but it displays a significantly different quaternary structure from that previously modeled [Fagagnini A et al., 2017, Biochem J 474, 3767-81], and based on the crystal structure of the RNase A N-terminal swapped dimer. ONC-D presents a variable quaternary assembly deriving from a variable open interface, while it retains a catalytic activity that is similar to that of ONC. Notably, ONC-D displays antitumor activity against two human melanoma cell lines, although it exerts a slightly lower cytostatic effect than the monomer. The inhibition of melanoma cell proliferation by ONC or ONC-D is associated with the reduction of the expression of the anti-apoptotic B cell lymphoma 2 (Bcl2), as well as of the total expression and phosphorylation of the Signal Transducer and Activator of Transcription (STAT)-3. Phosphorylation is inhibited in both STAT3 Tyr705 and Ser727 key-residues, as well as in its upstream tyrosine-kinase Src. Consequently, both ONC species should exert their anti-cancer action by inhibiting the pro-tumor pleiotropic STAT3 effects deriving either by its phospho-tyrosine activation or by its non-canonical signaling pathways. Both ONC species, indeed, increase the portion of A375 cells undergoing apoptotic cell death. This study expands the variety of RNase domain-swapped dimeric structures, underlining the unpredictability of the open interface arrangement upon domain swapping. Structural data also offer valuable insights to analyze the differences in the measured ONC or ONC-D biological activities.