Effect of Gamma Irradiation on Aflatoxins and Ochratoxin A Reduction in Almond Samples

The widespread contamination of food by mycotoxins may present a serious hazard to human and animal health. The gamma rays were applied to reduce ochratoxin A (OTA) and aflatoxins B1, B2, G1 and G2 (AFB1, AFB2, AFG1 and AFG2) in almonds artificially contaminated. In the present study we investigated the effect of gamma irradiation dosages, ranging from 0 to 15 kGy and the reduction of mycotoxins concentration in almond samples. In order to determine the efficiency of the method, a high-performance liquid chromatography method with fluorescence detection was used, the mycotoxins were extracted from almond samples and then purified with immunoaffinity columns. The maximum reduction was found at 15 kGy and it was 19.25%, 10.99%, 21.11%, 16.62%, 23.90% for AFB1, AFB2, AFG1, AFG2 and OTA respectively. Results showed that gamma radiations even at 15 kGy, were not effective in completely destroying aflatoxins and ochratoxin A.</p

VALUTAZIONE DELL'EFFETTO DEL TRATTAMENTO CON RADIAZIONI IONIZZANTI SUL CONTENUTO DI MICOTOSSINE NELLA FRUTTA SECCA

Le micotossine sono un gruppo eterogeneo di sostanze chimiche a basso peso molecolare prodotte dal metabolismo secondario di varie specie di funghi tossigeni appartenenti ai generi Aspergillus, Penicillum, Alternaria e Fusarium [1]. Sono molto resistenti al calore e non vengono completamente distrutte durante le normali operazioni di cottura, n\ue9 dai trattamenti fisici, chimici e biologici cui vengono normalmente sottoposte le derrate durante i processi di preparazione degli alimenti. La loro possibile presenza in molti alimenti costituisce oggi un motivo di crescente preoccupazione per la salute dei consumatori poich\ue9 alcune micotossine manifestano caratteristiche di genotossicit\ue0, cancerogenicit\ue0, immunotossicit\ue0, mutagenicit\ue0, nefrotossicit\ue0 e teratogenicit\ue0 [2-4]. Tra i metodi di decontaminazione esistenti ed ampiamente utilizzati, il trattamento degli alimenti con le radiazioni ionizzanti rappresenta un metodo sicuro per ottenere sia una migliore conservazione dei prodotti, sia un controllo delle affezioni alimentari, tramite la riduzione/eliminazione della popolazione patogena [5]. In questo lavoro sono stati valutati gli effetti del processo di irraggiamento con una sorgente di 60Co e dosi comprese tra 0,5 e 3 kGy sul contenuto di micotossine in campioni di frutta secca. In particolare il contenuto di aflatossine G1, G2, B1 e B2, e di ocratossina A (OTA) \ue8 stato valutato, prima e dopo l\u2019irraggiamento, attraverso cromatografia liquida ad alte prestazioni (HPLC) sfruttando le potenzialit\ue0 del rivelatore a fluorescenza. Le analisi HPLC sono precedute da un processo di purificazione del campione che prevede l\u2019utilizzo di colonne di immunoaffinit\ue0 [6-8]. Inoltre sono state valutate le relazioni esistenti tra dose e degradazione delle micotossine

Stitching proteins into membranes, not sew simple

Most integral membrane proteins located within the endomembrane system of eukaryotic cells are first assembled co-translationally into the endoplasmic reticulum (ER) before being sorted and trafficked to other organelles. The assembly of membrane proteins is mediated by the ER translocon, which allows passage of lumenal domains through and lateral integration of transmembrane (TM) domains into the ER membrane. It may be convenient to imagine multi-TM domain containing membrane proteins being assembled by inserting their first TM domain in the correct orientation, with subsequent TM domains inserting with alternating orientations. However a simple threading model of assembly, with sequential insertion of one TM domain into the membrane after another, does not universally stand up to scrutiny. In this article we review some of the literature illustrating the complexities of membrane protein assembly. We also present our own thoughts on aspects that we feel are poorly understood. In short we hope to convince the readers that threading of membrane proteins into membranes is 'not sew simple' and a topic that requires further investigation

Charge Pair Interactions in Transmembrane Helices and Turn Propensity of the Connecting Sequence Promote Helical Hairpin Insertion

α-Helical hairpins, consisting of a pair of closely spaced transmembrane (TM) helices that are connected by a short interfacial turn, are the simplest structural motifs found in multi-spanning membrane proteins. In naturally occurring hairpins, the presence of polar residues is common and predicted to complicate membrane insertion. We postulate that the pre-packing process offsets any energetic cost of allocating polar and charged residues within the hydrophobic environment of biological membranes. Consistent with this idea, we provide here experimental evidence demonstrating that helical hairpin insertion into biological membranes can be driven by electrostatic interactions between closely separated, poorly hydrophobic sequences. Additionally, we observe that the integral hairpin can be stabilized by a short loop heavily populated by turn-promoting residues. We conclude that the combined effect of TM¿TM electrostatic interactions and tight turns plays an important role in generating the functional architecture of membrane proteins and propose that helical hairpin motifs can be acquired within the context of the Sec61 translocon at the early stages of membrane protein biosynthesis. Taken together, these data further underline the potential complexities involved in accurately predicting TM domains from primary structures

NMR Investigation of Structures of G-Protein Coupled Receptor Folding Intermediates

Folding of G-protein coupled receptors (GPCRs) according to the two-stage model (Popot et al., Biochemistry 29(1990), 4031) is postulated to proceed in 2 steps: Partitioning of the polypeptide into the membrane followed by diffusion until native contacts are formed. Herein we investigate conformational preferences of fragments of the yeast Ste2p receptor using NMR. Constructs comprising the first, the first two and the first three transmembrane (TM) segments, as well as a construct comprising TM1-TM2 covalently linked to TM7 were examined. We observed that the isolated TM1 does not form a stable helix nor does it integrate well into the micelle. TM1 is significantly stabilized upon interaction with TM2, forming a helical hairpin reported previously (Neumoin et al., Biophys. J. 96(2009), 3187), and in this case the protein integrates into the hydrophobic interior of the micelle. TM123 displays a strong tendency to oligomerize, but hydrogen exchange data reveal that the center of TM3 is solvent exposed. In all GPCRs so-far structurally characterized TM7 forms many contacts with TM1 and TM2. In our study TM127 integrates well into the hydrophobic environment, but TM7 does not stably pack against the remaining helices. Topology mapping in microsomal membranes also indicates that TM1 does not integrate in a membrane-spanning fashion, but that TM12, TM123 and TM127 adopt predominantly native-like topologies. The data from our study would be consistent with the retention of individual helices of incompletely synthesized GPCRs in the vicinity of the translocon until the complete receptor is released into the membrane interior