Biomedical subjects

Ariane Schmechel

Publications and source records attributed to Ariane Schmechel.

4 recordsLinked to original sources

PubMed2004

Human BACE forms dimers and colocalizes with APP.

Beta-site APP-cleaving enzyme (BACE) is a membrane-bound aspartyl protease with no strict primary preference for cleavage. The molecular mechanisms that link the gamma-secretase multicomponent amyloid precursor protein (APP) processing complex to biochemical properties of BACE generating the N terminus of the amyloid beta-peptide have not, as yet, been identified. We found that in human brain tissue, BACE occurred as a dimer. The overall stability of the BACE homodimer was based on intermolecular interactions that were not affected by high salt, nonionic detergents or reducing conditions. BACE homodimers could only partially be separated even under strong denaturing conditions and revealed dramatic differences in the surface charge distribution compared with the monomer. In contrast, the soluble ectodomain of truncated BACE revealed a seemingly lower avidity to the prototypic aspartate protease inhibitor pepstatin and exclusively occurred in the monomeric form. Immunocytochemical studies colocalized APP and BACE in the plasma membrane of cells expressing endogenous levels of BACE and overexpressing APP. In cells that were cotransfected with APP and a putative active site D289A mutant of BACE, colocalization persisted. Remaining enzyme activity was found to be attributable to the mutant protease. Accordingly, inactivation of the carboxyl-terminal active site motif of BACE without an impairment of overall enzyme activity suggests that the enzyme may act as a dimer. Thus, homodimerization of BACE may help the enzyme to acquire specific mechanisms to associate with its substrates to exert catalytic activity.

Amyloid Precursor Protein Secretases↗

PubMed2004

Interaction kinetics of the copper-responsive CopY repressor with the cop promoter of Enterococcus hirae.

In Enterococcus hirae, copper homeostasis is controlled by the cop operon, which encodes the copper-responsive repressor CopY, the copper chaperone CopZ, and two copper ATPases, CopA and CopB. The four genes are under control of CopY, which is a homodimeric zinc protein, [Zn(II)CopY]2. It acts as a copper-responsive repressor: when media copper is raised, CopY is released from the DNA, allowing transcription to proceed. This involves the conversion of [Zn(II)CopY]2 to [Cu(I)2CopY]2, which is no longer able to bind to the promoter. Binding analysis of [Zn(II)CopY]2 to orthologous promoters and to control DNA by surface plasmon resonance analysis defined the consensus sequence TACAnnTGTA as the repressor binding element, or " cop box", of Gram-positive bacteria. Association and dissociation rates for the CopY-DNA interaction in the absence and presence of added copper were determined. The dissociation rate of [Zn(II)CopY]2 from the promoter was 7.3 x 10(-6) s(-1) and was increased to 5 x 10(-5) s(-1) in the presence of copper. This copper-induced change may be the underlying mechanism of copper induction. Induction of the cop operon was also assessed in vivo with a biosensor containing a lux reporter system under the control of the E. hirae cop promoter. Half-maximal induction of this biosensor was observed at 5 microM media copper, which delineates the ambient copper concentration to which the cop operon responds in vivo.

Bacterial Proteins↗

PubMed2003

Alzheimer beta-amyloid homodimers facilitate A beta fibrillization and the generation of conformational antibodies.

We reported previously that stabilized beta-amyloid peptide dimers were derived from mutant amyloid precursor protein with a single cysteine in the ectodomain juxtamembrane position. In vivo studies revealed that two forms of SDS-stable A beta homodimers exist, species ending at A beta 40 and A beta 42. The phenomenon of the transformation of the initially deposited 42-residue beta-amyloid peptide into the amyloid fibrils of Alzheimer's disease plaques remains to be explained in physical terms, i.e. energetically and structurally. We therefore performed spectroscopic analyses revealing that engineered dimeric peptides ending at residue 42 displayed a much more pronounced beta-structural transition than corresponding monomers. Specifically, the single chemically induced dimerization of A beta peptides significantly increased the beta-sheet content by a factor of 2. The C-terminal residues Ile-41 and Ala-42 of dimeric forms further increased the beta-sheet content by roughly one-third. In contrast to A beta 42, the beta-sheet content of the alpha- and gamma-secretase-generated p3 fragments did not necessarily correlate with the tendency to form fibrils, although p3/17-42 had a pronounced thread forming character with fibril lengths of up to 2.5 microM. Electron microscopic images show that forms of p3/17-42 generated smaller granular particles than forms ending at residue 40. We discuss these findings in terms of A beta 1-42 dimers representing paranuclei, which self-aggregate into ribbon-like ordered fibrils by elongation. Based on A beta 42 dimer-specific titers of a polyclonal antiserum we propose that the A beta homodimer represents a nidus for plaque formation and a well defined novel therapeutic target.

Amyloid beta-Peptides↗

PubMed2003

The Mason-Pfizer monkey virus PPPY and PSAP motifs both contribute to virus release.

Late (L) domains are required for the efficient release of several groups of enveloped viruses. Three amino acid motifs have been shown to provide L-domain function, namely, PPXY, PT/SAP, or YPDL. The retrovirus Mason-Pfizer monkey virus (MPMV) carries closely spaced PPPY and PSAP motifs. Mutation of the PPPY motif results in a complete loss of virus release. Here, we show that the PSAP motif acts as an additional L domain and promotes the efficient release of MPMV but requires an intact PPPY motif to perform its function. Examination of HeLaP4 cells expressing PSAP mutant virus by electron microscopy revealed mostly late budding structures and chains of viruses accumulating at the cell surface with little free virus. In the case of the PPPY mutant virus, budding appeared to be mostly arrested at an earlier stage before induction of membrane curvature. The cellular protein TSG101, which interacts with the human immunodeficiency virus type 1 (HIV-1) PTAP L domain, was packaged into MPMV in a PSAP-dependent manner. Since TSG101 is crucial for HIV-1 release, this result suggests that the Gag-TSG101 interaction is responsible for the virus release function of the MPMV PSAP motif. Nedd4, which has been shown to interact with viral PPPY motifs, was also detected in MPMV particles, albeit at much lower levels. Consistent with a role of VPS4A in the budding of both PPPY and PTAP motif-containing viruses, the overexpression of ATPase-defective GFP-VPS4A fusion proteins blocked both wild-type and PSAP mutant virus release.

Amino Acid Motifs↗