Sandbox Reserved 817

This Sandbox is Reserved from 06/12/2018, through 30/06/2019 for use in the course "Structural Biology" taught by Bruno Kieffer at the University of Strasbourg, ESBS. This reservation includes Sandbox Reserved 1480 through Sandbox Reserved 1543.

To get started: Click the edit this page tab at the top. Save the page after each step, then edit it again. Click the 3D button (when editing, above the wikitext box) to insert Jmol. show the Scene authoring tools, create a molecular scene, and save it. Copy the green link into the page. Add a description of your scene. Use the buttons above the wikitext box for bold, italics, links, headlines, etc. More help: Help:Editing

BACE1BACE1

spinqualitylabelsall models PDB ID 4ivs Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image
Crystal structure of BACE1 with its inhibitor, 4ivs
Ligands:
Activity:	Memapsin 2, with EC number 3.4.23.46
Related:	4ivt
Resources:	FirstGlance, OCA, RCSB, PDBsum
Coordinates:	save as pdb, mmCIF, xml

StructuresStructures

spinqualitylabelsall models Insert caption here Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

The 501 amino acid sequence of BACE1 bears the hallmark features of eukaryotic aspartic proteases of the pepsin family. BACE1 has two aspartic protease active site motifs, DTGS () and DSGT (), and mutation of either aspartic acid renders the enzyme inactive. Like other aspartic proteases, BACE1 has an N-terminal signal sequence (residues 1–21) and a pro-peptide domain (residues 22–45) that are removed post-translationally, so the mature enzyme begins at residue Glu46. Importantly, BACE1 has a single transmembrane domain near its C-terminus (residues 455–480) and a palmitoylated cytoplasmic tail. Thus, BACE1 is a type I membrane rotein with a luminal active site, features predicted for β-secretase. The position of the BACE1 active site within the lumen of intracellular compartments provides the correct topological orientation for cleavage of APP at the β-secretase site. As observed with other aspartic proteases, BACE1 has that form three intramolecular disulfide bonds and several N-linked glycosylation sites

Structurally, BACE1 belongs to the aspartyl protease family, and contains a bilobal structure forming by an N- and a C-terminal domains [12]. Both N- and C-domains are formed by highly twisted â-sheet structures and each domain contributes an aspartic acid to the catalytic module of the enzyme. It is thus proposed that ligands containing a positive charged moiety might be favorable to counteract the negative charged active site.

MechanismMechanism

The pattern and level of BACE1 expression is largely consistent with those of â-secretase activity in cells and tissues [23,24,50]. The levels of BACE1 mRNA are highest in brain and pancreas and are significantly lower in most other tissues. Moreover, BACE1 mRNA is highly expressed in neurons but little is found in resting glial cells of the brain, as expected for â-secretase. The protein is abundant in both normal human and AD brain [23,50]. Given the low levels of â-secretase activity in the pancreas, the high pancreatic mRNA expression was initially confusing [22]. However, subsequent reports indicated that BACE1 mRNA transcripts in pancreas largely consist of a splice variant missing the majority of exon 3 [51,52]. This splice variant encodes a BACE1 isoform devoid of â-secretase activity, thus reconciling the paradoxically high BACE1 mRNA levels with the low â-secretase activity found in the pancreas. The functional relevance of this pancreas-specific splice variant remains unclear. BACE1 induces a dramatic increase in â-secretase activity when transfected into stable APP-overexpressing cell lines. The immediate products of â-secretase cleavage, APPsâ and C99, are increased several fold over levels found in untransfected cells, and Aâ production is also elevated. Interestingly, APPsá levels are reduced upon BACE1 transfection, indicative that á- and â-secretases compete for APP substrate in cells. In contrast to the effects of BACE1 transfection, treatment of APP-overexpressing cells with BACE1 antisense oligonucleotides decreases BACE1 mRNA levels and inhibits â-secretase activity [23,24]. BACE1 antisense inhibition reduces production of APPsâ, C99, and Aâ in cells; conversely, APPsá and C83 generation is elevated. BACE1 cleaves APP only at the known â-secretase sites of Asp+1 and Glu+11 of Aâ . Moreover, purified recombinant BACE1 directly cleaves APP substrates at these same sites in vitro, demonstrating that the BACE1 molecule intrinsically exhibits protease activity [23,24]. The sequence specificity of purified BACE1 is the same as â- secretase. For example, it cleaves Swedish mutant APP substrate much more efficiently than wild type, and does not cleave a P1 Met-Val mutant substrate that is resistant to â-secretase cleavage. Like â-secretase, BACE1 has optimal activity at ~pH 4.5, is resistant to inhibition by pepstatin, and is localized within acidic subcellular compartments of the secretory pathway, primarily the Golgi apparatus, TGN and endosomes. Taken as a whole,the properties of BACE1 correlate very well with the previously established characteristics of â-secretase activity in cells and tissues.