TY - JOUR
T1 - Ubiquitin forms conventional decorated micelle structures with sodium dodecyl sulfate at saturation
AU - Mortensen, Henriette Gavlshøj
AU - Otzen, Daniel Erik
AU - Pedersen, Jan Skov
N1 - Copyright © 2021 Elsevier Inc. All rights reserved.
PY - 2021/8
Y1 - 2021/8
N2 - The anionic surfactant sodium dodecyl sulfate (SDS) interacts strongly with most globular proteins and denatures and unfolds them. While scattering studies using X-rays and neutrons have shown that this denaturation generally leads to protein-decorated SDS micelles, a different SDS-decorated polypeptide model has recently been suggested for complexes between SDS and Ubiquitin (UBI), in which individual SDS molecules are distributed on a partially stretched protein. To resolve this apparent discrepancy, we have investigated the SDS-UBI system by a number of complementary techniques. Small-angle X-ray scattering (SAXS) provides the overall structure of the SDS-UBI complexes, Tyr fluorescence and circular dichroism follow changes in tertiary and secondary structure, and isothermal titration calorimetry determines the stoichiometries of complexes and the amount of free SDS as a function of [SDS]. At low [SDS], UBI preserves its folded structure but dimerizes to a small extent. At 4 SDS per UBI, a complex is formed with two UBI and a small shared SDS cluster with 8 SDS molecules. In these complexes UBI preserves most of its native fold. At 10-12 SDS per UBI, which remains below the critical micelle concentration under our conditions, UBI-covered SDS micelles form with four UBIs around a core of 40 SDSs. This implies a protein-assisted micellization and an associated unfolding of UBI involving a change from mainly β-strands to mainly α-helical secondary structure. As [SDS] is increased, the complex gradually changes so that finally only one UBI covers one micelle with a similar number of SDS molecules at SDS saturation. Thus, we conclude that SDS unfolds UBI by mechanisms very similar to those observed for other globular proteins, leading to a protein-decorated SDS micelle rather than an SDS-decorated unfolded polypeptide chain.
AB - The anionic surfactant sodium dodecyl sulfate (SDS) interacts strongly with most globular proteins and denatures and unfolds them. While scattering studies using X-rays and neutrons have shown that this denaturation generally leads to protein-decorated SDS micelles, a different SDS-decorated polypeptide model has recently been suggested for complexes between SDS and Ubiquitin (UBI), in which individual SDS molecules are distributed on a partially stretched protein. To resolve this apparent discrepancy, we have investigated the SDS-UBI system by a number of complementary techniques. Small-angle X-ray scattering (SAXS) provides the overall structure of the SDS-UBI complexes, Tyr fluorescence and circular dichroism follow changes in tertiary and secondary structure, and isothermal titration calorimetry determines the stoichiometries of complexes and the amount of free SDS as a function of [SDS]. At low [SDS], UBI preserves its folded structure but dimerizes to a small extent. At 4 SDS per UBI, a complex is formed with two UBI and a small shared SDS cluster with 8 SDS molecules. In these complexes UBI preserves most of its native fold. At 10-12 SDS per UBI, which remains below the critical micelle concentration under our conditions, UBI-covered SDS micelles form with four UBIs around a core of 40 SDSs. This implies a protein-assisted micellization and an associated unfolding of UBI involving a change from mainly β-strands to mainly α-helical secondary structure. As [SDS] is increased, the complex gradually changes so that finally only one UBI covers one micelle with a similar number of SDS molecules at SDS saturation. Thus, we conclude that SDS unfolds UBI by mechanisms very similar to those observed for other globular proteins, leading to a protein-decorated SDS micelle rather than an SDS-decorated unfolded polypeptide chain.
KW - Complex formation
KW - Protein-surfactant interactions
KW - SAXS
KW - Structure determination
UR - http://www.scopus.com/inward/record.url?scp=85104137819&partnerID=8YFLogxK
U2 - 10.1016/j.jcis.2021.03.110
DO - 10.1016/j.jcis.2021.03.110
M3 - Journal article
C2 - 33845230
SN - 0021-9797
VL - 596
SP - 233
EP - 244
JO - Journal of Colloid and Interface Science
JF - Journal of Colloid and Interface Science
ER -