The solution structure and stability of N-terminally truncated b2-microglobulin~DN6b2-m!, the major modification in ex vivo fibrils, have been investigated by a variety of biophysical techniques. The results show that DN6b2-m has a free energy of stabilization that is reduced by 2.5 kcal0mol compared to the intact protein. Hydrogen exchange of a mixture of the truncated and full-length proteins at mM concentrations at pH 6.5 monitored by electrospray mass spectrometry reveals that DN6b2-m is significantly less protected than its wild-type counterpart. Analysis of DN6b2-m by NMR shows that this loss of protection occurs in b strands I, III, and part of II. At mM concentration gel filtration analysis shows that DN6b2-m forms a series of oligomers, including trimers and tetramers, and NMR analysis indicates that strand V is involved in intermolecular interactions that stabilize this association. The truncated species of b2-microglobulin was found to have a higher tendency to self-associate than the intact molecule, and unlike wild-type protein, is able to form amyloid fibrils at physiological pH. Limited proteolysis experiments and analysis by mass spectrometry support the conformational modifications identified by NMR and suggest that DN6b2-m could be a key intermediate of a proteolytic pathway of b2-microglobulin. Overall, the data suggest that removal of the six residues from the N-terminus of b2-microglobulin has a major effect on the stability of the overall fold. Part of the tertiary structure is preserved substantially by the disulfide bridge between Cys25 and Cys80, but the pairing between b-strands far removed from this constrain is greatly perturbed.Keywords: amyloidosis; b2-microglobulin; hydrogen exchange mass spectrometry; limited proteolysis; NMR; protein folding Amyloidoses are diseases caused by tissue deposition of protein aggregate organized in an ordered b-sheet structure. The conversion of globular proteins to insoluble fibrillar aggregates requires significant conformational changes, such as the loss of tertiary and quaternary interactions or conversion of a to b secondary structurẽ Sunde & Blake, 1998!. Of the 17 or so proteins implicated in amyloidoses the fibril morphology is indistinguishable and there does not appear to be any common features that link the soluble precursor proteins. For many of these proteins, the amyloid fibril formation is facilitated by amino acid mutations that destabilize the native state and confer a structural flexibility to the molecule, but other proteins like IAPP, wild-type TTR, and b2-microglobulin

SummaryCopper is an essential yet toxic metal and its overload causes Wilson disease, a disorder due to mutations in copper transporter ATP7B. To remove excess copper into the bile, ATP7B traffics toward canalicular area of hepatocytes. However, the trafficking mechanisms of ATP7B remain elusive. Here, we show that, in response to elevated copper, ATP7B moves from the Golgi to lysosomes and imports metal into their lumen. ATP7B enables lysosomes to undergo exocytosis through the interaction with p62 subunit of dynactin that allows lysosome translocation toward the canalicular pole of hepatocytes. Activation of lysosomal exocytosis stimulates copper clearance from the hepatocytes and rescues the most frequent Wilson-disease-causing ATP7B mutant to the appropriate functional site. Our findings indicate that lysosomes serve as an important intermediate in ATP7B trafficking, whereas lysosomal exocytosis operates as an integral process in copper excretion and hence can be targeted for therapeutic approaches to combat Wilson disease.

The prototypic long pentraxin PTX3 is a unique fluid-phase pattern recognition receptor that plays a nonredundant role in innate immunity and female fertility. The PTX3 C-terminal domain is required for C1q recognition and complement activation and contains a single N-glycosylation site on Asn 220. In the present study, we characterized the structure of the human PTX3 glycosidic moiety and investigated its relevance in C1q interaction and activation of the complement classical pathway. By specific endo and exoglycosidases digestion and direct mass spectrometric analysis, we found that both recombinant and naturally occurring PTX3 were N-linked to fucosylated and sialylated complex-type sugars. Interestingly, glycans showed heterogeneity mainly in the relative amount of bi, tri, and tetrantennary structures depending on the cell type and inflammatory stimulus. Enzymatic removal of sialic acid or the entire glycosidic moiety equally enhanced PTX3 binding to C1q compared to that in the native protein, thus indicating that glycosylation substantially contributes to modulate PTX3/C1q interaction and that sialic acid is the main determinant of this contribution. BIAcore kinetic measurements returned decreasing K(off) values as sugars were removed, pointing to a stabilization of the PTX3/C1q complex. No major rearrangement of PTX3 quaternary structure was observed after desialylation or deglycosylation as established by size exclusion chromatography. Consistent with C1q binding, PTX3 desialylation enhanced the activation of the classical complement pathway, as assessed by C4 and C3 deposition. In conclusion, our results provided evidence of an involvement of the PTX3 sugar moiety in C1q recognition and complement activation.

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Glycosylation of integrins has been implicated in the modulation of their function. Characterisation of carbohydrate moieties of alpha(3) and beta(1) subunits from non-metastatic (WM35) and metastatic (A375) human melanoma cell lines was carried out on peptide-N-glycosidase F-released glycans using matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS). beta(1) integrin subunit from both cell lines displayed tri- and tetraantennary oligosaccharides complex type glycans, but only in A375 cell line was the sialylated tetraantennary complex type glycan (Hex(7)HexNAc(6)FucSia(4)) present. In contrast, only alpha(3) subunit from metastatic cells possessed beta1-6 branched structures. Our data indicate that the beta(1) and alpha(3) subunits expressed by the metastatic A375 cell line carry beta1-6 branched structures, suggesting that these cancer-associated glycan chains may modulate tumor cell adhesion by affecting the ligand binding properties of alpha(3)beta(1) integrin. In direct ligand binding assays, alpha(3)beta(1) integrin from both cell lines binds strongly to fibronectin and to much lesser degree to placental laminin. No binding to collagen IV was observed. Enzymatic removal of sialic acid residues from purified alpha(3)beta(1) integrin stimulates its adhesion to all examined ECM proteins. Our data suggest that the glycosylation profile of alpha(3)beta(1) integrin in human melanoma cells correlates with the acquisition of invasive capacity during melanoma progression.

This paper describes the cloning of the genes coding for each component of the complex of toluene/o-xylene monooxygenase from Pseudomonas stutzeri OX1, their expression, purification and characterization. Moreover, the reconstitution of the active complex from the recombinant subunits has been obtained, and the functional role of each component in the electron transfer from the electron donor to molecular oxygen has been determined.The coexpression of subunits B, E and A leads to the formation of a subcomplex, named H, with a quaternary structure (BEA) 2 , endowed with hydroxylase activity.Tomo F component is an NADH oxidoreductase. The purified enzyme contains about 1 mol of FAD, 2 mol of iron, and 2 mol of acid labile sulfide per mol of protein, as expected for the presence of one [2Fe)2S] cluster, and exhibits a typical flavodoxin absorption spectrum.Interestingly, the sequence of the protein does not correspond to that previously predicted on the basis of DNA sequence. We have shown that this depends on minor errors in the gene sequence that we have corrected.C component is a Rieske-type ferredoxin, whose iron and acid labile sulfide content is in agreement with the presence of one [2Fe)2S] cluster. The cluster is very sensitive to oxygen damage.Mixtures of the subcomplex H and of the subunits F, C and D are able to oxidize p-cresol into 4-methylcathecol, thus demonstrating the full functionality of the recombinant subunits as purified.Finally, experimental evidence is reported which strongly support a model for the electron transfer. Subunit F is the first member of an electron transport chain which transfers electrons from NADH to C, which tunnels them to H subcomplex, and eventually to molecular oxygen.Keywords: monooxygenase; protein expression; electron transfer; bioremediation; recombinant.Several strains from Pseudomonas genus grow on aromatic compounds due to enzymatic systems able to activate aromatic rings by mono-and di-hydroxylations and to operate ortho or meta-cleavage pathway [1,2] which leads to citric acid cycle intermediates.Toluene/o-xylene-monooxygenase (Tomo) from Pseudomonas stutzeri OX1 [3,4] is endowed with a broad spectrum of substrate specificity [3], and the ability to hydroxylate more than a single position of the aromatic ring in two consecutive monooxygenation reactions [3]. Thus Tomo is able to oxidize o-, m-and p

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Cisplatin (CDDP) can be encapsulated within the central cavity of reconstituted (apo)ferritin, (A)Ft, to form a drug-loaded protein of potential great interest for targeted cancer treatments. In this study, the interactions occurring between cisplatin and native horse spleen Ft in CDDP-encapsulated AFt are investigated by high-resolution X-ray crystallography. A protein bound Pt center is unambiguously identified in AFt subunits by comparative analysis of difference Fourier electron density maps and of anomalous dispersion data. Indeed, a [Pt(NH3)2H2O](2+) fragment is found coordinated to the His132 residue located on the inner surface of the large AFt spherical cage. Remarkably, Pt binding does not alter the overall physicochemical features (shape, volume, polarity/hydrophobicity and electrostatic potential) of the outer surface of the AFt nanocage. CDDP-encapsulated AFt appears to be an ideal nanocarrier for CDDP delivery to target sites, as it possesses high biocompatibility and can be internalized by receptor mediated endocytosis, thus carrying the drug to tumor tissue with higher selectivity than free CDDP.