The amino acid sequence of cytochrome c-556 from Agrobacterium tumefaciens strain Apple 185

NMR-validated structural model for oxidized Rhodopseudomonas palustris cytochrome c 556

The structure of oxidized Rhodopseudomonas palustris cytochrome c(556) has been modeled after that of high-spin cytochrome c' from the same bacterium, the latter being the protein with the greatest sequence identity (35%) among all sequenced proteins in the genomes. The two proteins differ in the number of ligands to iron and in spin state, the former being six-coordinate low-spin and the latter five-coordinate high-spin. In order to validate this modeled structure, several structural restraints were obtained by performing a restricted set of NMR experiments, without performing a complete assignment of the protein signals. The aim was to exploit the special restraints arising from the paramagnetism of the metal ion. A total of 43 residual-dipolar-coupling and 74 pseudocontact-shift restraints, which together sampled all regions of the protein, were used in conjunction with over 40 routinely obtained NOE distance restraints. A calculation procedure was undertaken combining the program MODELLER and the solution structure determination program PARAMAGNETIC DYANA, which includes paramagnetism-based restraints. The directions and magnitude of the magnetic susceptibility anisotropy tensor were also calculated. The approach readily provides useful results, especially for paramagnetic metalloproteins of moderate to large dimensions.

Identification of a metalloprotease from Alzheimer's disease brain able to degrade the beta-amyloid precursor protein and generate amyloidogenic fragments

A 4.2-kDa polypeptide termed beta protein (A beta) accumulates in senile plaques and blood vessels in Alzheimer's disease and Down's syndrome. It is widely believed that A beta is the product of the posttranslational processing of a larger precursor protein, the beta amyloid precursor protein (APP). The proteolytic processes involved in the generation of the A beta are virtually unknown. Here the purification and characterization of a protease from Alzheimer's disease brain capable of cleaving a 10 amino acid synthetic substrate flanking the N terminus of A beta at the Met-Asp bond are described. Most importantly, the purified protease degrades human recombinant APP and generates a 15-kDa amyloidogenic fragment. The protease requires the presence of a reducing agent for its activity. Its pH optimum is around physiological pH, while the enzyme is inactive at acidic pH (below pH 5.0) and basic pH (over pH 7.6). The enzyme is inhibited by N-ethylmaleimide, (hydroxymercuri)benzoate, 1.10-phenanthroline, EDTA, and EGTA. Phenylmethanesulfonyl fluoride has no effect on its activity. This protease is devoid of caseinolytic or gelatinase activities, as well as activities against cathepsin B and cathepsin L substrates. Sequence analysis reveals high homology to the rat metallopeptidase EC 3.4.24.15, a protease involved in neuropeptide processing.

Aberrant proteolysis of the beta-amyloid precursor protein in familial Alzheimer's disease lymphoblastoid cells

Lymphoblastoid cells from patients with early-onset and late-onset familial Alzheimer's disease showed increased expressions of beta-amyloid precursor mRNA and protein as well as interleukin-1 and alpha 1-antichymotrypsin protein. Early-onset and late-onset familial Alzheimer's disease cells had greater production of 16-kDa beta-amyloid C-terminal preamyloid peptides than did normal cells. A pulse-chase experiment indicated that aberrant processing of this peptide resulted in its abnormal accumulation. Furthermore, the peptide prepared from early-onset familial Alzheimer's disease cells using formic acid could be separated into four discrete fragments. The N-terminal amino acid sequencing of each fragment indicated that the 16-kDa peptide was generated by cleavage, principally at the 30 amino acids N-terminal to beta-amyloid. Both the enhanced synthesis and aberrant processing of the beta-amyloid precursor protein, therefore, are basic processes associated with familial Alzheimer's disease lymphoblastoid cells.

Erythroid transcription factor NF-E2 is a haematopoietic-specific basic-leucine zipper protein

Expression of globin genes in developing erythroid cells is controlled by upstream locus control regions. Activity of these regions in vivo requires an erythroid-specific nuclear factor (NF-E2) that binds AP-1-like recognition sites. Its tissue-specific component (p45 NF-E2) has been characterized by complementary DNA cloning as a new basic region-leucine zipper protein which dimerizes with a ubiquitous partner to form native NF-E2.

A calcium-activated protease from Alzheimer's disease brain cleaves at the N-terminus of the amyloid beta-protein

Alzheimer's disease, Down's syndrome, and to a far lesser extent, normal aged brains exhibit abnormal extracellular deposits of amyloid. The major component of brain amyloid is the beta-protein, a 4Kd fragment of the larger beta-protein precursor. The finding of the abnormally processed beta-protein and a protease inhibitor (alpha 1-antichymotrypsin) in the amyloid deposits prompted us to search for proteases which may generate the beta-protein from its precursor. We now report on the presence and partial purification of one such proteolytic activity from Alzheimer's brain. Normal physiologic C-terminal cleavage of the secreted form of the beta-protein precursor occurs in the middle of the beta-protein suggesting that the beta-protein accumulates due to an alternative degradation pathway. We propose here that the protease activity we describe participates in this abnormal pathway.