Beta-amyloid (Ab) deposition in the brain is the hallmark of Alzheimer's Disease (AD), a neurodegenerative disorder characterized by progressive loss of memory and cognition in the elderly. An initial step involves proteolytic cleavage of amyloid precursor protein (APP, chromosome 21) releasing short 40, 42 & 43 aa peptides (beta amyloid 1-40, 1-42, and 1-43). Polymerization of b-amyloid (Ab) and subsequent neuronal deposit (amyloid) leads to the degeneration of neurons involved in memory and cognition. Mutations in the APP gene cause some forms of familial AD (FAD) by releasing an increased amounts of b-amyloid. To initiate Ab formation, b-secretase cleaves APP at the N-terminus of Ab to release APPsb (~100 kDa soluble NT-fragment), and C99, a 12-kDa CT membrane fragment. Alternatively, a-secretase cleaves within the Ab to prevent the formation of Ab. Cleavage by a-secretase produces a soluble N-terminal fragment, APPsa, and a 10-kDa membrane C-terminal fragment, C83. Both C99 and C83 can be further cleaved by g-secretase releasing Ab and a nonpathogenic p3 peptide, respectively. Both Presenilins and a newly discovered protein, Nicastrin are required for this activity. Nicastrin may act to position the APP stub correctly to allow presenilin to cut it at the right place; or it might regulate the activity of the g-secretase enzyme (possibly presenilin). Suppression of nicastrin expression in C. elegans embryos induces a subset of notch/glp-1 phenotypes similar to those induced by simultaneous null mutations in both presenilin homologues of C. elegans (sel-12 and hop-1). Nicastrin also binds carboxy-terminal fragment of b-APP, and alter the production of the amyloid b-peptide. Missense mutations in a conserved hydrophilic domain of nicastrin increase Ab42 and Ab40 peptide production, whereas deletions in this domain inhibit Ab production. It would thus appear that nicastrin and presenilins might be part of the multimeric protein complex "secretosme" necessary for the intramembranous proteolysis of proteins such as Notch/GLP-1 and bAPP.

Human nicastrin gene (chromosome 1) encodes a transmembrane protein of 709 aa (mouse 708 aa). It has a putative signal peptide; a long N-terminal hydrophilic domain containing glycosylation, N-myristoylation and phosphorylation motifs; a 20-residue hydrophobic putative transmembrane domain; and a short hydrophilic carboxy terminus of 20 residues. Human nicastrin has 89% homology with the mouse and 30% with Drosophila's protein.

Two metalloproteases, ADAM 10 (a disintegrin and metalloproteases) and TACE (TNF-a converting enzyme) are the candidates for a-secretase. TACE (mouse/rat 827 aa, human 824) belongs to the family of membrane-anchored glycoprotein. It has been shown to correct process APP and the model APP substrates in vitro.

Recently, BACE (Beta-site APP Cleaving Enzyme) has been cloned, purified, and identified as b-secretase. BACE belongs to the family of Aspartyl proteases (Asp) also known as Memapsins (membrane associated aspartic proteases). At least four related Asps, located on chromosome IV and X, have been cloned (Asp1, Asp2, Asp3, and Asp4). Human BACE/Asp2/Memapsin 2 located on chromosome 11, is a transmembrane protein of 501 aa. It has an amino terminal signal peptide (1-21 aa), a proprotein domain (22-45 aa), one transmembrane domain near the C-terminus, and a short cytoplasmic C-terminal tail of 24 aa. The mature protein extends from 46-460 aa. The lumenal portion of BACE has two active site motifs at 93 aa and 289 aa with signature sequence of aspartic proteases. BACE has 30% sequence homology with pepsin family of proteases. Rat and mouse BACE (501 aa) are 96% identical with human BACE. BACE expression was most prominent in most areas of the rat brain and pancreas. BACE is approx 70 kDa, greater than the theoretical size of ~51 kDa, due to glycosylation. It has been localized in the compartments of the secretory pathways including the golgi apparatus, transgolgi network, secretory vesicles and endosomes. Purified BACE/Asp2 cleaves APP and synthetic APP peptide substrate at the b-secretase site, and the rate of cleavage is increase 10-fold by a Swedish type mutation associated with early onset of Alzheimer's disease.

BACE2 or Asp1/Memapsin2 (human 518, mouse 514 aa) resides in the obligate Down Syndrome regions of chromosome 21. BACE2, 52% identity with BACE/Asp2, is most divergent at the N and C-terminus, but display the same protein topology as BACE. BACE2, like BACE, is expressed in brain and several tissues and cell lines. However, experiments using BACE2 antisense in cells suggest that it is unlikely to be the principal b-secretase.

ADI has produced antibodies to BACE and BACE2 using specific peptides sequences. The appropriate control immunogenic peptides are also available to confirm specificity of antibodies. In addition, synthetic purified peptides that can serve as substrates for b-Secretase enzyme activity are also available.
  
 

m=mouse; r=rat; h=human; b=bovine; d=dog; ~CT or ~NT=near C or N-terminus. EC=Extracellular; CP=Cytoplasmic domain;

* Expected antibody crossreactivity information is mostly based upon high (>70%) sequence conservation of antigenic/control peptides in various species. When antibody crossreactivity has actually been experimentally confirmed in various species, it will be mentioned in the appropriate data sheets.

"Neat Antisera or antisera" are the unpurified antiserum and it is suitable for ELISA and Western.
"Affinity pure" IgG may be more suitable for immunohistochemical (IHC) applications and to reduce background in most immunological applications including ELISA and Western.
"Control peptides" can not be used for Western as they are very short peptides. They are intended for ELISA or antibody blocking studies to establish antibody specificity.
Western blot +ve protein controls, where available, are semi-pure, pure or recombinant proteins that are formulated in SDS-PAGE sample buffer. They are recommended to be used for Western (load 10 ul/lane) for visulaization with antibodies.

All Products are for in vitro research use only. rev 40720A

List of Publications using ADI's antibodies for BACE.

Bace2, Vattemi, Gaetano 2003 Experimental Neurology, Volume 179, Issue 2, February 2003, Pages 150-158 BACE1 and BACE2 in pathologic and normal human muscle WB, IHC human muscle.

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