Tetramerization of the S100B Chaperone Spawns a Ca2+ Independent Regulatory Surface that Enhances Anti-aggregation Activity and Client Specificity.
J Mol Biol
; 434(19): 167791, 2022 10 15.
Article
in En
| MEDLINE
| ID: mdl-35970403
ABSTRACT
Alzheimer's disease (AD) hallmarks include the aggregation of amyloid-ß (Aß), tau and neuroinflammation promoted by several alarmins. Among these is S100B, a small astrocytic homodimeric protein, upregulated in AD, whose multiple biological activities depend on localization, concentration, and assembly state. S100B was reported to inhibit the aggregation and toxicity of Aß42 and tau similarly to a holdase-type chaperone. This activity is dependent of Ca2+-binding, which triggers the exposure of a regulatory binding cleft at the S100B dimer interface with which amyloidogenic clients dynamically interact. Although the dimer prevails, a significant portion of secreted S100B in the human brain occurs as higher order multimers, whose protective functions remain uncharacterized and which we here investigate. Resorting to ThT-monitored aggregation kinetics, we determined that unlike the dimer, tetrameric S100B inhibits Aß42 aggregation at sub/equimolar ratios, an effect that persists in the absence of Ca2+ binding. Structural analysis revealed that S100B tetramerization spawns a novel extended cleft accommodating an aggregation-prone surface that mediates interactions with monomeric Aß client via hydrophobic interactions, as corroborated by Bis-ANS fluorescence and docking analysis. Correspondingly, at high ionic strength that reduces solvation and favours hydrophobic contacts, the inhibition of Aß42 aggregation by tetrameric S100B is 3-fold increased. Interestingly, this extended Ca2+-independent surface favours Aß42 as substrate, as tau K18 aggregation is not inhibited by the apo tetramer. Overall, results illustrate a mechanism through which oligomerization of the S100B chaperone fine-tunes anti-aggregation activity and client specificity, highlighting the potential functional relevance of S100B multimers in the regulation of AD proteotoxicity.
Key words
Full text:
1
Collection:
01-internacional
Database:
MEDLINE
Main subject:
Calcium
/
Molecular Chaperones
/
Alzheimer Disease
/
S100 Calcium Binding Protein beta Subunit
/
Protein Aggregation, Pathological
Limits:
Animals
/
Humans
Language:
En
Journal:
J Mol Biol
Year:
2022
Document type:
Article