Transmission of methicillin-resistant Staphylococcus aureus via deceased donor liver transplantation confirmed by whole genome sequencing.

Donor-derived bacterial infection is a recognized complication of solid organ transplantation (SOT). The present report describes the clinical details and successful outcome in a liver transplant recipient despite transmission of methicillin-resistant Staphylococcus aureus (MRSA) from a deceased donor with MRSA endocarditis and bacteremia. We further describe whole genome sequencing (WGS) and complete de novo assembly of the donor and recipient MRSA isolate genomes, which confirms that both isolates are genetically 100% identical. We propose that similar application of WGS techniques to future investigations of donor bacterial transmission would strengthen the definition of proven bacterial transmission in SOT, particularly in the presence of highly clonal bacteria such as MRSA. WGS will further improve our understanding of the epidemiology of bacterial transmission in SOT and the risk of adverse patient outcomes when it occurs.

SR proteins ASF/SF2 and SRp55 participate in tissue factor biosynthesis in human monocytic cells.

BACKGROUND: Human monocytes express two naturally occurring forms of circulating tissue factor (TF) - full-length TF, a membrane-spanning protein, and alternatively spliced TF, a soluble molecule. Presence of the variable exon 5 in TF mRNA determines whether the encoded TF protein is transmembrane, or soluble. Recently, an essential SR protein ASF/SF2 was implicated in TF pre-mRNA processing in human platelets. OBJECTIVE: To examine molecular mechanisms governing regulated processing of TF pre-mRNA in human monocytic cells. METHODS AND RESULTS: In silico analysis of the human TF exon 5, present only in full-length TF mRNA, revealed putative binding motifs termed exonic splicing enhancers (ESE) for the SR proteins ASF/SF2 and SRp55, which were found to be abundantly expressed in monocytic cell lines THP-1 and SC, as well as monocyte-enriched peripheral blood mononuclear cells (PBMC). Using a splice competent mini-gene reporter system transiently expressed in monocytic cells, it was determined that weakening of either five closely positioned ASF/SF2 ESE (bases 87-117) or a single conserved SRp55 ESE (base 39) results in severe skipping of exon 5. ASF/SF2 and SRp55 were found to physically associate with the identified ESE. CONCLUSIONS: SR proteins ASF/SF2 and SRp55 appear to interact with the variable TF exon 5 through ESE at bases 39 and 87-117. Weakening of the above ESE modulates splicing of TF exon 5. This study is the first to identify and experimentally characterize cis-acting splicing elements involved in regulated biosynthesis of human TF.

Origin and properties of fluorescence emission from the extrinsic 33 kDa manganese stabilizing protein of higher plant water oxidizing complex.

The fluorescence properties of the isolated extrinsic 33 kDa subunit acting as 'manganese stabilizing protein' (MSP) of the water oxidizing complex in photosynthesis was analyzed in buffer solution. Measurements of the emission spectra as a function of excitation wavelength, pH and temperature led to the following results: (a) under all experimental conditions the spectra monitored were found to be the composite of two contributions referred to as '306 nm band' and 'long-wavelength band', (b) the excitation spectra of these two bands closely resemble those of tyrosine and tryptophan in solution, respectively, (c) the spectral shape of the '306 nm band' is virtually independent on pH but its amplitude drastically decreases in the alkaline with a pK of 11.7, (d) the amplitude of the 'long-wavelength' emission band at alkaline pH slightly increases when the pH rises from 7.2 to about 11.3 followed by a sharp decline at higher pH, and (e) the shape of the overall spectrum at pH 7.2 is only slightly changed upon heating to 90 degrees C whereas the amplitude significantly declines. Based on these findings the two distinct fluorescence bands are ascribed to tyrosine(s) ('306 nm band') and the only tryptophan residue W241 of MSP from higher plants ('long-wavelength band') as emitters which are both embedded into a rather hydrophobic environment.

pH-induced transition and Zn2+-binding properties of bovine prolactin.

A pH-induced conformational transition was found in bovine prolactin within the physiologically significant pH region from 6.5 to 8.5. The thermal stability of prolactin at pH 6.5 is essentially higher than at pH 8.5. Bovine prolactin binds zinc ions with an apparent association constant of 2 x 10(5) M(-1) at pH 6.5 and 1 x 10(4) M(-1) at pH 8.5. The pH dependence of both thermal stability and zinc binding surrounding the pKa of histidine suggests that these residues plays a key role in the structural integrity of bovine prolactin.

Interactions of alpha-lactalbumins with lipid vesicles studied by tryptophan fluorescence.

Complexes of alpha-lactalbumin (alpha-LA)1 with dimyristoylphosphatidylcholine (DMPC) or dipalmitoylphosphatidylcholine (DPPC) liposomes at pH 8 and at pH 2 have been obtained by means of gel filtration. Thermal denaturation of alpha-LA complexes of DMPC or DPPC at pH 8 was found to depend on the saturation of protein by metal cations. The intrinsic fluorescence of DMPC-alpha-LA and DPPC-alpha-LA was sensitive to two thermal transitions. The first transition corresponded to the Tc of the lipid vesicles, while the second transition arose from the denaturation of the protein. Fluorescence spectrum position suggested that at low temperature tryptophan accessibility increases upon protein-DMPC or protein-DPPC association. At temperatures above the protein transition (70 degrees C) tryptophan appears to interact significantly with the apolar phase of DMPC and DPPC, evidenced by spectral blue shifts. Whereas the free protein at pH 2 adopts the molten globule (MG) state and is characterized by the absence of a thermal transition, the rapidly-isolated DMPC-alpha-LA complex was characterized by the appearance of a distinct fluorescence thermal transition between 50 and 60 degrees C. This result is consistent with a model of a partially-inserted form of alpha-LA which may possess some degree of tertiary structure and therefore unfolds cooperatively.

[Study of conformation transitions in proteins by tryptophan fluorescence and phosphorescence at low temperatures]. / Issledovanie konformatsionnykh perekhodov v belkakh po triptofanovoi fluorestsentsii i fosforestsentsii pri nizkikh temperaturakh.

The well-known conformational changes in proteins containing a single tryptophan residue, such as pH-induced N-->F transition in human serum albumin, pH-induced acidic transition in cod parvalbumin, and KCl-induced tetramerization of bee venom melittin were monitored by changes in low temperature phosphorescence and fluorescence spectra suggesting two independent series of normal components. Parameters of low temperature tryptophan luminescence were sensitive to chromophore environment. A correlation of changes of some spectral parameters with accessibility of tryptophan to water was revealed, however, spectral changes mainly depend on specific interactions of the chromophore with its environment.

[Analytical description of electron-vibrational protein spectra]. / Analiticheskoe opisanie élektronno-kolebatel'nykh spelktrov belkov.

Electron-vibrational spectra of phosphorescence and fluorescence of tryptophan residues in proteins at 77 K are best approximated by theoretical curves computed according to a model which suggests the existence of two independent series of Gaussian vibrational components. Each series contains one type of vibrations. Phosphorescence and fluorescence spectra of proteins with various localizations of their single tryptophan residue were fitted by a curve computed according to this model. The results obtained show that the phosphorescence band of tryptophan residues in proteins seems to contain two types of vibrations with frequencies 650-800 cm-1 and 1350-1500 cm-1. Since the substitution of H2O by D2O does not change the frequencies of both vibrations in the phosphorescence spectra of human serum albumin, melittin and tryptophan in 1 M KCl, it is reasonable to suggest that the 1350-1500 cm-1 series corresponds to the W5 type vibrations (B19a type of vibrations of benzene ring). The 650-800 cm-1 series"can be identified with W18 type of vibrations (breathing vibrations of indole ring). Phosphorescence parameters of tryptophan residues in proteins correlate with their fluorescence parameters.

[Kinetics of dissociation of parvalbumin complexes with calcium and magnesium ions]. / Kinetika dissotsiatsii kompleksov parval'bumina s ionami kal'tsiia i magniia.

Dissociation kinetics of parvalbumin complexes with calcium and magnesium ions were studied by means of stopped-flow method employing intrinsic protein fluorescence registration. In the temperature range from 10 to 30 degrees C the kinetic curves of Ca2+ and Mg2+ dissociation are best fitted with a sum of two exponential terms, each term is ascribed to a dissociation process in one of two bindings sites of parvalbumin. Dissociation rate constants in this temperature range increase from 0.03 to 0.8 s-1 and from 0.18 to 5 s-1 for Ca2+, and from 0.9 to 4.5 s-1 and from 4 to 33 s-1 for Mg2+. Parvalbumin equilibrium binding constants of Ca2+ and Mg2+ were also measured in the same temperature range. It makes possible to estimate the rate constants of association of Ca2+ and Mg2+. In the case of Ca2+ the rate of association approaches the diffusion controlled limit.