Selectively increased oxidative modifications mapped to detergent-insoluble forms of Abeta and beta-III tubulin in Alzheimer's disease.
Deleterious post-translational modifications (PTMs) to the neuronal cytoskeleton are a proposed mechanistic link between accumulation of amyloid (A) beta peptides and subsequent abnormalities of tau and neurodegeneration in Alzheimer's disease (AD). Here we tested the hypothesis that PTMs on neuronal tubulins selectively accumulate in a pathological protein fraction in AD. We used new software, P-MOD, to identify comprehensively and map PTMs using mass spectral data from soluble (normal) and detergent-insoluble (pathological) protein fractions from AD, as well as total extracts from controls, for selected proteins: Abeta, tau, apolipoprotein (apo) E, glial fibrillary acidic protein (GFAP), alpha-III tubulin, and beta-III tubulin. Our results confirmed direct observations of others by identifying methionine (M) sulfoxides at Abeta position 35 and numerous sites of tau phosphorylation in detergent-insoluble protein from AD, while no PTMs were enriched on primarily astrocyte-derived apoE or GFAP in this fraction. P-MOD mapped several abundant M sulfoxides to neuron-enriched beta-III tubulin but not its heterodimeric partner, neuron-enriched alpha-III tubulin, a result confirmed by selective suppression of CNBr-mediated cleavage of beta-III tubulin. These findings are the first comprehensive assessment of PTMs in AD and point to oxidative modification of beta-III tubulin as a potential contributor to the neuronal cytoskeletal disruption that is characteristic of AD.
Boutte
Angela M
AM
Center for Molecular Neuroscience, Vanderbilt University, Nashville, Tennessee, USA.
Woltjer
Randall L
RL
Zimmerman
Lisa J
LJ
Stamer
Sheryl L
SL
Montine
Kathleen S
KS
Manno
Michael V
MV
Cimino
Patrick J
PJ
Liebler
Daniel C
DC
Montine
Thomas J
TJ
D000544:Alzheimer Disease / Q000378:metabolism*; D016564:Amyloid beta-Protein Precursor / Q000378:metabolism*; D001344:Autopsy; D001921:Brain / Q000378:metabolism / Q000473:pathology; D003599:Cytoskeleton / Q000378:metabolism / Q000473:pathology; D003902:Detergents; D006801:Humans; D009474:Neurons / Q000378:metabolism / Q000473:pathology; D010084:Oxidation-Reduction; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D012016:Reference Values; D013702:Temporal Lobe / Q000378:metabolism* / Q000473:pathology; D014404:Tubulin / Q000378:metabolism*; D016875:tau Proteins / Q000378:metabolism
D016564:Amyloid beta-Protein Precursor; D003902:Detergents; C498585:TUBB3 protein, human; D014404:Tubulin; D016875:tau Proteins