The fluorescent monomeric protein Kusabira Orange. Pressure effect on its structure and stability

The structure and stability of the fluorescent protein monomeric Kusabira Orange (mKO), a GFP-like protein, was studied under different pressure levels and in different chemical environments. At different pH values (between pH 7.4 and pH 4.0) and under a pressure up to 600 MPa (at 25 °C), mKO did not show significant fluorescence spectral changes, indicating a structural stability of the protein. In more extreme chemical conditions (at pH 4.0 in the presence of 0.8 M guanidine hydrochloride), a marked reduction of mKO fluorescence intensity emission was observed at pressures above 300 MPa. This fluorescence emission quenching may be due to the loss of the intermolecular bonds and, consequently, to the destructuration of the mKO chromophore structure. Since the electrostatic and hydrophobic interactions as well as the salt bridges present in proteins are usually perturbed under high pressure, the reduction of mKO fluorescence intensity emission is associated to the perturbation of the protein salt bridges network.

Amino acid transport in thermophiles: characterization of an arginine-binding protein from Thermotoga maritima. 3. Conformational dynamics and stability

Arginine-binding protein from Thermotoga maritima (TmArgBP) is a 27.7 kDa protein possessing the typical two domain structure of the periplasmic binding protein family. The protein is characterized by high specificity and affinity for binding a single molecule of l-arginine. In this work, the effect of temperature and/or guanidine hydrochloride on structure and stability of the protein in the absence and in the presence of l-arginine has been investigated by differential scanning calorimetry, far-UV circular dichroism and intrinsic tryptophan phosphorescence and fluorescence. The results revealed that TmArgBP undergoes an irreversible one-step thermal unfolding process in a cooperative mode. The TmArgBP melting temperature was recorded at 115 °C. The presence of l-arginine did not change the protein secondary structure content as well as the intrinsic phosphorescence and fluorescence protein properties, even if it increases the structural stability of the protein. The obtained results are discussed in combination with a detailed inspection of the three-dimensional structure of the protein.

[In vitro activity of fosfomycin]

The in vitro activity of phosphomycin has been compared with other antibiotics in 1703 bacterial strains isolated from pathological specimens sent to the Laboratory from various divisions of the hospital. Results were first class on both gram-positive and gram-negative flora. It was in first place as regards staphylococcus (97.4% sensitive strains), citrobacter (68.6%), proteus mirabilis (73.1%), indole positive proteus (48.2%). It also predominated in pseudomonas (54.6%) and E. coli (86.7%). In view of the fact that gram-negative infections are taking on a predominant position within the hospital environment, it is considered that phosphomycin should be rightfully included among the antibacterial drugs in routine use.