1,721,052 research outputs found
Biological activity and pathological implications of misfolded proteins.
No full textThe physiological metabolism of proteins guarantees that different cellular compartments contain the appropriate concentration of proteins to perform their biological functions and, after a variable period of wear and tear, mediates their natural catabolism. The equilibrium between protein synthesis and catabolism ensures an effective turnover, but hereditary or acquired abnormalities of protein structure can provoke a premature loss of biological function, an accelerated catabolism and diseases caused by the loss of an irreplaceable function. In certain proteins, abnormal structure and metabolism are associated with a strong tendency to self-aggregation into a polymeric fibrillar structure, and in these cases the disease is not principally caused by the loss of an irreplaceable function but by the action of this new biological entity. Amyloid fibrils are an apparently inert, insoluble, mainly extracellular protein polymer that kills the cell without tissue necrosis but by activation of the apoptotic mechanism. We analyzed the data reported so far on the structural and functional properties of four prototypic proteins with well-known biological functions (lysozyme, transthyretin, beta 2-microglobulin and apolipoprotein AI) that are able to create amyloid fibrils under certain conditions, with the perspective of evaluating whether the achievement of biological function favors or inhibits the process of fibril formation. Furthermore, studying the biological functions carried out by amyloid fibrils reveals new types of protein-protein interactions in the transmission of messages to cells and may provide new ideas for effective therapeutic strategies
THE PISCINE PLASMA RETINOL-BINDING PROTEIN. PURIFICATION, PARTIAL AMINO ACID SEQUENCE AND INTERACTION WITH MAMMALIAN TRANSTHYRETIN OF RAINBOW TROUT (ONCORHYNCHUS MYKISS) RETINOL-BINDING PROTEIN
No full text1. Retinol-binding protein (RBP) has been isolated from the pooled plasma or rainbow trouts (Oncorhinchus mykiss) by gel filtration, hydrophobic interaction chromatography and ion-exchange chromatography. By this procedure two forms of the protein, both with a molecular mass (approximately 20 kDa) similar to that of mammalian RBP, were purified to homogeneity. Five amino acid substitutions have been found in the partial (about 60%) sequences of the two forms of trout RBP, which are presumably acetylated at their N terminus. The apparent participation of six conserved cysteines in the formation of disulphide bridges, as in human RBP, and the similarity (about 60%) of the amino acid sequence of trout and mammalian RBPs, indicate the existence of a similar overall structure organization in evolutionary distant RBPs. 2. Although the two forms of trout RBP are not physiologically involved in the formation of any protein--protein complex in plasma, they are capable of interacting with mammalian transthyretin, albeit with a binding affinity (K'd = 15-40 microM) considerably lower than that of mammalian RBP. Our data indicate that the two forms of trout RBP also possess the region that in mammalian RBP has the functional role of binding transthyretin. It is suggested that transthyretin (or a homologous protein) was modified, during phylogenetic development of the non mammalian vertebrates, to acquire a binding site for such a region of the RBP molecule
Nanotechnology drives a paradigm shift on protein misfolding diseases and amyloidosis
Full text linkIn almost a century of scientific work on the mechanism of amyloid diseases much of the attention has been focused on the amyloid fibrils, which still represent the diagnostic hallmark of the disease and are easily identified in affected organs for their peculiar tinctorial properties and the fibrillar shape. However, it has been lately discovered that the seeds of the pathogenesis are deeply hidden in the structure and folding dynamics of proteins at the monomeric state which almost indistinguishable from the normal counterpart through classical biochemical approaches. In the recent years soluble oligomeric/prefibrillar species, putatively cytotoxic, were discovered and even more recently polymorphisms of shape and structure of fibrils was emerging as a property that could dictate the bioactivity of amyloid as well as the specificity of its tissue localization. Nanotechnology through the biophysical analysis of the single molecules (monomers or oligomers or fibrils) is the propulsive disciplines in the transformation of our knowledge on the molecular mechanism of this disease. It will provide, in the forthcoming years, precious analytical devices mimicking the biological microenvironment where the molecular events causing the amyloid formation will be monitored and possibly modulated in a real time frame
Systemic amyloidosis: lessons from β2-microglobulin.
Full text linkβ2-Microglobulin is responsible for systemic amyloidosis affecting patients undergoing long-term hemodialysis. Its genetic variant D76N causes a very rare form of familial systemic amyloidosis. These two types of amyloidoses differ significantly in terms of the tissue localization of deposits and for major pathological features. Considering how the amyloidogenesis of the β2-microglobulin mechanism has been scrutinized in depth for the last three decades, the comparative analysis of molecular and pathological properties of wild type β2-microglobulin and of the D76N variant offers a unique opportunity to critically reconsider the current understanding of the relation between the protein's structural properties and its pathologic behavior
THE PRIMARY STRUCTURE OF PISCINE (ONCORHYNCHUS MYKISS) RETINOL-BINDING PROTEIN AND A COMPARISON WITH THE THREE-DIMENSIONAL STRUCTURE OF MAMMALIAN RETINOL-BINDING PROTEIN
No full text1. The primary structures of two variants of rainbow trout (Oncorhynchus mykiss) plasma retinol-binding protein (RBP) were determined and found to be approximately 60% identical with those of both human and Xenopus laevis RBPs. The comparable sequence similarities that we have found agree with the estimate of similar divergence times between bony fishes and mammals and between bony fishes and amphibians. The two piscine RBP variants differ by six amino acid substitutions at positions that are not crucial for the interaction with retinol, on the basis of the human RBP three-dimensional structure [Cowan, S. W., Newcomer, M. E. & Jones, T. A. (1990) Proteins Struct. Func. Genet. 8, 44-61]. 2. Models were developed for the three-dimensional structures of rainbow trout and X. laevis RBPs, based on that of human RBP. The overall three-dimensional structure appears to be very well preserved for RBPs isolated from vertebrate species for which the divergence time is 350-400 million years. At variance with an almost absolute conservation for the residues that participate in the formation of the retinol binding site in mammalian RBPs, several amino acid replacements are found for this part of the RBP molecule when the comparison is extended to piscine and amphibian RBPs. However, the only allowed amino acid replacements are either conservative or more than 0.4 nm distant from retinol. Besides the retinol binding site, a few regions at the protein surface appear to be rather conserved during phylogenetic development of vertebrates and, therefore, might be involved in molecular interactions
Phosphorylation of human hnRNP protein A1 abrogates in vitro strand annealing activity
No full textIn HeLa cells metabolically labeled in vivo with [32P] orthophosphate in the presence of okadaic acid the concentration of phosphorylated A1 protein was increased significantly as compared to controls. Purified recombinant hnRNP protein A1 served as an excellent substrate in vitro for the catalytic subunit of cAMP-dependent protein kinase (PKA) and for casein kinase II (CKII). Thin layer electrophoresis of A1 acid hydrolysates showed the protein to be phosphorylated exclusively on serine residue by both kinases. V8 phosphopeptide maps revealed that the target site(s) of in vitro phosphorylation are located in the C-terminal region of A1. Phosphoamino acid sequence analysis and site directed mutagenesis identified Ser 199 as the sole phosphoamino acid in the protein phosphorylated by PKA. Phosphorylation introduced by PKA resulted in the suppression of the ability of protein A1 to promote strand annealing in vitro, without any detectable effect on its nucleic acid binding capacity. This finding indicates that phosphorylation of a single serine residue in the C-terminal domain may significantly alter the properties of protein A1
Structural characterization of kappa II Inc, a new amyloid immunoglobulin
No full textLight chain Inc, obtained from a patient with amyloid arthropathy, has an Mr of 23,550 and consists of 219 amino acid residues. The complete primary structure of its variable domain has been determined by sequence analysis of the corresponding tryptic peptides, aligned by fragments derived from cyanogen bromide digestion, and by partially sequencing the intact protein. Although closely related to protein of the V kappa II subgroup, light chain Inc differs from its counterpart by the replacement of some invariant residues in its variable domain. By comparing its sequence with that of the nonamyloid kappa II Nim, a different distribution of some polar and apolar amino acid residues through the molecule is evidenced. A computer graphic analysis shows that some of the replaced amino acid residues cannot be readily accommodated in the known three-dimensional structure of the immunoglobulin light chains
- …
