[Show abstract][Hide abstract] ABSTRACT: Mildly denaturing conditions induce bovine alpha-crystallin, the major structural lens protein, to self-assemble into fibrillar structures in vitro. The natural dipeptide l-carnosine has been shown to have potential protective and therapeutic significance in many diseases. Carnosine derivatives have been proposed as potent agents for ophthalmic therapies of senile cataracts and diabetic ocular complications. Here we report the inhibitory effect induced by the peptide (l- and d-enantiomeric form) on alpha-crystallin fibrillation and the almost complete restoration of the chaperone activity lost after denaturant and/or heat stress. Scanning force microscopy (SFM), thioflavin T, and a turbidimetry assay have been used to determine the morphology of alpha-crystallin aggregates in the presence and absence of carnosine. DSC and a near-UV CD assay evidenced that the structural precursors of amyloid fibrils are polypeptide chain segments that lack stable structural elements. Moreover, we have found a disassembling effect of carnosine on alpha-crystallin amyloid fibrils. Finally, we show the ability of carnosine to restore most of the lens transparency in organ-cultured rat lenses exposed to similar denaturing conditions that were used for the in vitro experiments.
[Show abstract][Hide abstract] ABSTRACT: Molecular weight and size distributions of two glutenin polymers were determined by a multi-angle laser light scattering (MALLS) photometer on-line to a size exclusion chromatography (SEC) system. Two glutenin polymers extracted, sonicated and purified from wheat flours of different cultivars, i.e. Cheyenne and Chinese Spring, were accurately fractionated by SEC using three buffers (pH 2.6, 4.0 and 6.9) and two column sets. Both molecular weight distribution (MWD) and radius of gyration distribution (RGD) could be used to differentiate the two cultivars. MWD of glutenin polymers is a complex mixture of high- and low-molecular weight fractions and the relative percentage was found to be very different. The two cultivars were found to be different; in particular, the Chinese Spring polymer showed more compact conformation than the Cheyenne polymer. The slope of the conformation plot for glutenin was about 0.37, close to the theoretical value for compact spheres. Determination of glutenin MWD and RGD was difficult and depended on the buffer used and the SEC columns.
No preview · Article · Sep 2008 · Journal of Cereal Science
[Show abstract][Hide abstract] ABSTRACT: alpha-Crystallin in its native state is a large, heterogeneous, low-molecular weight (LMW) aggregate that under certain conditions may progressively became part of insoluble high-molecular weight (HMW) systems. These systems are supposed to play a relevant role in eye lens opacification and vision impairment. In this paper, we report the effects of trehalose on alpha-crystallin aggregates. The role of trehalose in alpha-crystallin stress tolerance, chaperone activity and thermal stability is studied. The results show that trehalose stabilizes the alpha-crystallin native structure, inhibits alpha-crystallin aggregation, and disaggregates preformed LMW systems not affecting its chaperone activity.
Full-text · Article · Apr 2007 · Biochemical and Biophysical Research Communications
[Show abstract][Hide abstract] ABSTRACT: The verification of the cDNA-deduced sequence of the high molecular weight glutenin subunit 1Bx7 in Chinese Spring cultivar was achieved by direct matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) analysis of the tryptic fragments. The published sequence of the 1Bx7 subunit contains 5 Lys and 15 Arg residues but, due to the presence of three Arg-Pro bonds, which are generally resistant to cleavage by trypsin, or cleaved to a very limited extent by trypsin, 19 peptides can be predicted. The identification of the tryptic fragments was achieved by direct MALDI-MS analysis by using three different matrices (DHB, SA and HCCA) in combination with the most compatible sample preparation procedures in order to obtain the maximum sequence coverage. MALDI analysis of the 1Bx7 tryptic digest resulted in the identification of the expected peptides and additional fragments arising from non-specific cleavages; the fragments that were not detected are peptides with low mass (from 147.2 to 317.4), so we obtained a sequence coverage of 98.8%. The results reported here also indicated that the sequence of the 1Bx7 subunit from cv. Chinese Spring is different from the cDNA-deduced sequence reported in the literature; in particular, a possible insertion of the hexapeptide QPGQGQ within the sequence Gln630-Tyr725 was suggested. Finally, it is possible to rule out glycosylation of the 1Bx7 subunit, or any other post-translational modification, to within the detection limits of the method.
No preview · Article · Jul 2005 · Rapid Communications in Mass Spectrometry