The folding and aggregation properties of a single KH-domain protein: Ribosome binding factor A (RbfA) from Pseudomonas aeruginosa

BACKGROUND

Ribosome-binding factor A from the pathogenic bacterium Pseudomonas aeruginosa (PaRbfA) is a small ribosome assembly factor, composed by a single KH domain, involved in the maturation of the 30S subunit. These domains are characterized by the ability to bind RNA or ssDNA and are often located in proteins involved in a variety of cellular functions. However, although the ability of proteins to fold properly, to misfold or to aggregate is of paramount importance for their cellular functions, limited information is available on these dynamic properties in the case of KH domains.

METHODS

PaRbfA thermodynamic stability and folding mechanism: Far-UV CD and fluorescence spectroscopy, stopped-flow kinetics and chevron plot analysis, site-directed mutagenesis. Fibrils characterization: FT-IR spectroscopy, Thioflavin T fluorescence, Transmission Electron Microscopy (TEM) and X-ray fibrils diffraction.

RESULTS

Quantitative analysis of the (un)folding kinetics of PaRbfA show that, in vitro, the protein folds via a 3-states mechanism involving a transiently populated folding intermediate. We also provide experimental evidences that PaRbfA can form ordered fibrils endowed with cross-β structure even in mild conditions.

CONCLUSION

These results lead to the hypothesis that the folding intermediate of PaRbfA may expose (some of) the predicted amyloidogenic regions, which could act as aggregation nuclei in the fibrillogenesis.

GENERAL SIGNIFICANCE

The methodological approach presented herein could be readily adapted to verify the ability of other KH domain proteins to form cross-β structured fibrils and to transiently populate a folding intermediate.

Structural investigation of nucleophosmin interaction with the tumor suppressor Fbw7γ

Nucleophosmin (NPM1) is a multifunctional nucleolar protein implicated in ribogenesis, centrosome duplication, cell cycle control, regulation of DNA repair and apoptotic response to stress stimuli. The majority of these functions are played through the interactions with a variety of protein partners. NPM1 is frequently overexpressed in solid tumors of different histological origin. Furthermore NPM1 is the most frequently mutated protein in acute myeloid leukemia (AML) patients. Mutations map to the C-terminal domain and lead to the aberrant and stable localization of the protein in the cytoplasm of leukemic blasts. Among NPM1 protein partners, a pivotal role is played by the tumor suppressor Fbw7γ, an E3-ubiquitin ligase that degrades oncoproteins like c-MYC, cyclin E, Notch and c-jun. In AML with NPM1 mutations, Fbw7γ is degraded following its abnormal cytosolic delocalization by mutated NPM1. This mechanism also applies to other tumor suppressors and it has been suggested that it may play a key role in leukemogenesis. Here we analyse the interaction between NPM1 and Fbw7γ, by identifying the protein surfaces implicated in recognition and key aminoacids involved. Based on the results of computational methods, we propose a structural model for the interaction, which is substantiated by experimental findings on several site-directed mutants. We also extend the analysis to two other NPM1 partners (HIV Tat and CENP-W) and conclude that NPM1 uses the same molecular surface as a platform for recognizing different protein partners. We suggest that this region of NPM1 may be targeted for cancer treatment.

Effects of chronic antipsychotic treatment on neurophysiological correlates of the auditory oddball task in schizophrenia: A preliminary report from a multicentre study

Introduction

The effects of chronic antipsychotic administration on the human brain are debated. In particular, first-generation (FGAs) and second-generation antipsychotics (SGAs) seem to have different impacts on brain function and structure in subjects with schizophrenia. Few studies have investigated the effect of chronic administration of FGAs and SGAs on indices of brain function, such as event-related potentials (ERP) or neuropsychological performance.

Objectives

Within the Italian Network for Research on Psychoses study, subjects stabilized on FGAs or SGAs were compared on P300, an ERP component, thought to reflect attention, working memory and context integration and on neurocognitive indices.

Methods

ERPs were recorded in 110 chronic, stabilized patients with Schizophrenia (28 used FGAs) during a standard auditory oddball task. P300 latency and amplitude were assessed at Pz channel. MATRICS Consensus Cognitive Battery (MCCB) was used for cognitive assessment.

Results

Compared with the SGAs group, patients on FGAs showed significant increased P300 latency (P = 0.003; Cohen's d = 0.67) and significant decreased P300 amplitudes (P = 0.023; Cohen's d = 0.38). The two groups did not differ on psychopathology and MCCB scores. Multiple linear regressions revealed that “FGAs vs. SGAs” (β = 0.298, P = 0.002) and MCCB neurocognitive composite T-score (β = –0.273, P = 0.004) were independent predictors of P300 latency, whereas only age (β = –0.220, P = 0.027) was an independent predictor of P300 amplitude.

Conclusions

FGAs seem to affect the functional brain activity more than SGAs, particularly slowing cortical processing. Our results suggest that discrepant findings concerning P300 latency in schizophrenia might be related to the type of antipsychotic treatment used. Longitudinal studies are needed to further address this issue.

Disclosure of interest

The authors have not supplied their declaration of competing interest.

Relation between EEG source functional connectivity and the negative symptom severity in schizophrenia: a preliminary report from a multicentre study

Introduction

Neural dysconnectivity is hypothesized to be a key element in pathophysiology of schizophrenia. However, the relation of disordered connectivity with the different clinical characteristics of the syndrome is not fully elucidated.

Objectives

The current research investigated the relations between resting-state EEG Source Functional Connectivity (EEG-SFC) and the two main clusters of negative symptoms derived from the Brief Negative Symptom Scale, the Expressive Deficit (ED) and the Avolition (AV), in subjects with schizophrenia (SCZ) enrolled to the multicentre study of the Italian Network for Research on Psychoses.

Methods

Out of 97 chronic, stabilized SCZ included, we selected subjects according the lower and the upper quartile of the ED and AV value distribution: 25 were in upper and 24 in the lower quartile of ED (respectively, HIGH-ED and LOW-ED); 27 were in upper and 24 in the lower quartile of AV (respectively, HIGH-AV and LOW-AV). Fifty-five healthy controls (HC) were included, comparable to SCZ for gender, age and educational level. EEG-SFC analysis was based on the lagged phase synchronization (LPS) computed by eLORETA from 5 minutes resting-state EEG recordings in eyes closed condition. LPS indices were determined for each spectrum band and between all 28 regions of interest (ROI) pairs. Group differences were significant for corrected P-value < 0.05.

Results

SCZ had higher theta band LPS than HC. Respect to LOW-ED, HIGH-ED showed significant increased alpha LPS in fronto-cingulate, para-hippocampal and insular inter-hemispheric ROI pairs. No significant difference emerged between HIGH-AV and LOW-AV.

Conclusions

Subgrouping SCZ according to negative symptom severity reveals heterogeneous patterns of resting-state LPS connectivity.

Disclosure of interest

The authors have not supplied their declaration of competing interest.

Covalently immobilized RGD gradient on PEG hydrogel scaffold influences cell migration parameters

Understanding the influence of a controlled spatial distribution of biological cues on cell activities can be useful to design "cell instructive" materials, able to control and guide the formation of engineered tissues in vivo and in vitro. To this purpose, biochemical and mechanical properties of the resulting biomaterial must be carefully designed and controlled. In this work, the effect of covalently immobilized RGD peptide gradients on poly(ethylene glycol) diacrylate hydrogels on cell behaviour was studied. We set up a mechanical device generating gradients based on a fluidic chamber. Cell response to RGD gradients with different slope (0.7, 1 and 2 mM cm(-1)) was qualitatively and quantitatively assessed by evaluating cell adhesion and, in particular, cell migration, compared to cells seeded on hydrogels with uniform distribution of RGD peptides. To evaluate the influence of RGD gradient and to exclude any concentration effect on cell response, all analyses were carried out in a specific region of the gradients which displayed the same average concentration of RGD (1.5 mM). Results suggest that cells recognize the RGD gradient and adhere onto it assuming a stretched shape. Moreover, cells tend to migrate in the direction of the gradient, as their speed is higher than that of cells migrating on hydrogels with a uniform distribution of RGD and increases by increasing RGD gradient steepness. This increment is due to an augmentation of bias speed component of the mean squared speed, that is, the drift of the cell population migrating on the anisotropic surface provided by the RGD gradient.

Impression cytology with scanning electron microscopy: a new method in the study of conjunctival microvilli

PURPOSE

Recent studies used impression cytology with scanning electron microscopy (SEM) to study the conjunctival surface of bovine eyes and normal human eyes. The purpose of this study was to evaluate the use impression cytology and SEM (ICSEM) in patients affected by tear film abnormalities.

METHODS

Forty-five patients were divided into three groups according to mild, moderate or severe subjective sensation of dry eye. Fifteen asymptomatic subjects served as control group. In all patients the tear film was evaluated with break-up time (BUT), Schirmer's, and Ferning test, whereas conjunctival epithelium was evaluated with impression cytology and optic microscopy (ICOM), and ICSEM. The Spearman rank correlation test was used to compare the outcome of these examinations with the subjective sensation of dry eye in each group, and to identify correlations among the five tests.

RESULTS

ICSEM findings highly correlated with subjective dry eye sensation (Spearman correlation coefficient, 796; P<0.01). ICSEM revealed incipient epithelial damage (reduction or absence of microvilli) before the appearance of alterations of nucleus and cytoplasm of epithelial cells revealed by optic microscopy. The number of microvilli was correlated with the degree of tear film abnormalities and subjective sensation of dry eye (Spearman correlation coefficient, 796; P<0.01).

CONCLUSION

ICSEM was very effective in detecting the reduction in the number of microvilli. Therefore, it could represent an effective method to detect alterations in the conjunctival epithelium resulting from tear film damage even before the epithelial damage occurs and is detected by optic microscopy.

Miniaturized metalloproteins: application to iron-sulfur proteins

The miniaturization process applied to rubredoxins generated a class of peptide-based metalloprotein models, named METP (miniaturized electron transfer protein). The crystal structure of Desulfovibrio vulgaris rubredoxin was selected as a template for the construction of a tetrahedral (S(gamma)-Cys)(4) iron-binding site. Analysis of the structure showed that a sphere of 17 A in diameter, centered on the metal, circumscribes two unconnected approximately C(2) symmetry related beta-hairpins, each containing the -Cys-(Aaa)(2)-Cys- sequence. These observations provided a starting point for the design of an undecapeptide, which self assembles in the presence of tetrahedrally coordinating metal ions. The METP peptide was synthesized in good yield by standard methodologies. Successful assembly of the METP peptide with Co(II), Zn(II), Fe(II/III), in the expected 2:1 stoichiometry, was proven by UV-visible and circular dichroism spectroscopies. UV-visible analysis of the metal complexes indicated the four Cys ligands tetrahedrally arrange around the metal ion, as designed. Circular dichroism measurements on both the free and metal-bound forms revealed that the metal coordination drives the peptide chain to fold into a turned conformation. NMR characterization of the Zn(II)-METP complex fully supported the structure of the designed model. These results prove that METP reproduces the main features of rubredoxin.