Title: BACE 1
1BACE 1 Alzheimers Disease
- By Anisha Vora Lindsey Wood
2What is Alzheimers?
- Neurodegenerative disorder characterized by the
progressive and irreversible loss of nerve cells
(neurons) located in the specific brain areas
the hippocampus and polymodal association areas - 4th leading cause of death in adults (cases rise
with aging) - Cortical brain areas heavily filled with two
different types of lesions amyloid plaques and
neurofibriallary tangles - Amyloid plaques spherical extracellular amyloid
deposits - Neurofibrillary tangles an intra-neuronal
accumulation of pathological fibrils called
Paired Helical Filaments (PHF) basis of these
tangles is the tau protein
3Why this disease?
- Prevalence is increasing
- United States and Congress has classified the
treatment of this disease as a major national
priority - 100 billion per year is spent on Alzheimer's
disease in the United States, making it the third
most costly disease after heart disease and
cancer - 7 million Americans may be afflicted by the year
2010
4Plaques Tangles
- Disrupt all three processes
- Communication (sending messages)
- Metabolism (turning chemicals and nutrients into
energy to keep neurons working) - Repair (keeping long-lived neurons in good
working order) - Cause nerve cells to stop working, lose
connections w/ other cells and eventually die - Destruction causes memory failure, personality
changes, etc. - Find abundance of ß-amyloid plaques and
neurofibrillary tangles, especially in regions
for memory
5The Changing Brain
- PET scan measures blood and glucose metabolism
giving map of active brain - Damage by free radicals increase
- Shrinking of neurons
- Increased levels of tangles plaques develop in
AD
Normal Brain
Alzheimers Brain
6Neurofibrillary Tangles
- Insoluble twisted fibers found inside of brains
cells - Primarily tau, which forms part of structure
called a microtubule - Microtubule helps transport nutrients and other
important substance from one part of nerve cell
to another - In AD, tau is abnormal and microtubule structures
collapse
7Neurofibrillary Tangles
8ß-Amyloid Plaques
- Dense, insoluble deposits made of 42 residue
ß-amyloid peptides - Arranged in an anti-parallel arrangement
- Fragments clump together and are mixed w/
molecules, neurons and non-nerve cells - Develop in hippocampus (deep in brain, encode
memories) and later in other areas of cerebral
cortex (those involved thinking and making
decisions)
9Amyloid Precursor Protein
APP is associated with the cell membrane, the
thin barrier that encloses the cell. After it is
made, APP sticks through the neuron's membrane,
partly inside and partly outside the cell.
10From APP to ß-amyloid
Enzymes act on the APP and cut it into fragments
of protein, one of which is called beta-amyloid.
11From APP to ß-amyloid
The beta amyloid fragments begin coming together
into clumps outside the cell, then join other
molecules and non-nerve cells to form insoluable
plaques.
12Overall Mechanism of AD formation
13BACE 1
- ß-Secretase (BACE-1 for ß-site APP-cleaving
enzyme) is a type 1 transmembrane protein
containing aspartyl protease activity - 501 amino acids
- Mediates the primary amyloidogenic cleavage of
APP - Generates a membrane-bound APP C-terminal
fragment-immediate precursor for the
intramembraneous ?-secretase cleavage. - BACE-1 is the only protease with a well-defined
ß-secretase activity shown by the homozygous
knockout of the BACE-1 gene, which does not allow
any Aß generation - (Cai et al, 2001 Luo et al, 2001).
14APP Cleavage Sites
153 proteases
- Three proteases, alpha-, ß- and gamma-secretases,
are involved in APP processing. - At the cell surface, APP undergoes proteolysis by
alpha-secretase releasing a large, soluble
ectodomain (a-APP sAPP). The C-terminal fragment
is retained within the cell membrane. - This fragment can then be cleaved by
gamma-secretase releasing the p3 peptide. - In an alternate pathway, ß-secretase cleaves APP
releasing a large secreted derivative sAPPß and a
C-terminal fragment CTFß that can be further
cleaved by gamma-secretase to form Aß which is
released into the extracellular region.
16Cleavage Diagram
17Structure of BACE 1 complexed with inhibitor
(Hong et al, 2000),
- Resolution found to 1.9 Angstroms
- 4 domains
- Lumenal domain, transmembrane domain, cytosol
c-terminal tail - Active site is more open and less hydrophobic
than other human proteases
18Function of BACE 1
- Responsible for the proteolytic processing of the
amyloid precursor protein (APP). - Cleaves at the N-terminus of the A-beta peptide
sequence, between residues 671 and 672 of APP, - Leads to the generation and extracellular release
of beta-cleaved soluble APP, and a corresponding
cell-associated C-terminal fragment which is
later released by gamma-secretase. - BACE-1 expression is significantly enhanced in
brains from patients with AD - Reasons for the enhanced expression are currently
unclear. Speculated that AD-associated stressors
such as oxidative stress, radicals, unfolded
proteins, head trauma, and others may induce
BACE-1 transcription and/or expression/activity
during aging
19Cleavage of APP, APLP1, and APLP2 by BACE 1
20Drug Targeting for AD
- BACE-1 is an obvious target for Aß-lowering
drugs. - In contrast to ?-secretase, BACE-1 can be fully
knocked out in mice without causing any bad
phenotypes. Interfering with BACE-1 is unlikely
to result in unwanted side effects. - The three-dimensional structure of BACE-1 has
been solved and peptidomimetic and
nonpeptidomimetic inhibitors have already been
generated (Hong et al, 2000 Vassar, 2001). - Developed further to improve their affinity with
the rather large active site cleft of BACE-1
before they can be used in human trials.
21Inhibitors of BACE 1 invitro
Table 1. In vitro values Cp P3 P1' X BACE FRET
HEK293 Aß inhibition at P3 IC50(uM)a
IC50(uM)a 1 CHMe2 Me N 0.082 (0.023)
2.831 (0.129) 2 H H 9.704 (1.413)
gt100 3 Me H 0.285 (0.016)
gt100 4 Me N 4.925 (0.169)
gt100 5 Me H 2.397 (0.089)
gt100 6 CHMe2 Me N 0.260(0.002) 5.305
(0.191) 7 (S)-MeCHEt(Ile) MeN 0.065
(0.039) 0.880 (0.042) a Values are means
of three experiments, standard deviation is given
in parentheses.
22BACE-1 Inhibitors
- Macrocycles derived from a hydroxyethylene core
structure - Molecule inhibits production of Aß peptide in
HEK293 cells overexpressing APP751sw - Improve potency, Val residue at the P3 position
replaced with Ile (compound 7)
23BACE-1 Inhibitory Complex
- Compound 7 co-crystallized with BACE-1
- X-ray structure of complex elucidated at 1.6Å
resolution to an R-factor of 0.211 using data
from the Advanced Photon Source
24Future Exploration with BACE 1
- Try to modify inhibitors to have a higher
affinity for BACE 1 active site - Decrease formation of AB42 and aggregate creation
- Further cleavage of AB42 to eliminate plaques
- Breakdown of beta amyloid plaques formed in the
brain
25Questions?