Complexes of native ubiquitin and dodecyl sulfate illustrate the nature of hydrophobic and electrostatic interactions in the binding of proteins and surfactants.
Complexes of native ubiquitin and dodecyl sulfate illustrate the nature of hydrophobic and electrostatic interactions in the binding of proteins and surfactants.
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DOI：
10.1021/ja205735q
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发表时间：
2011-11-09
影响因子：
15
通讯作者：
Whitesides, George M.
中科院分区：
文献类型：
--
作者：
Shaw, Bryan F.;Schneider, Gregory F.;Arthanari, Haribabu;Narovlyansky, Max;Moustakas, Demetri;Durazo, Armando;Wagner, Gerhard;Whitesides, George M.
先前的一项研究，使用毛细管电泳（CE），报告了六个离散的复合物的泛素（UBI）和十二烷基硫酸钠（SDS）形成在不同浓度的SDS沿着的途径，以解折叠的SDS溶液中。一种复合物（在0.8和1.8 mM SDS之间形成）由与约11个SDS分子缔合的天然UBI组成。目前的研究使用CE和15 N/13 C-1H杂原子单量子相干（HSQC）NMR光谱来鉴定折叠UBI中与0.8-1.8 mM SDS特异性相关的残基，并将这些关联与这种充分表征的蛋白质的既定生物物理和结构特性相关联。使用CE，通过将lys-ε-NH3+转化为lys-ε-NHCOCH 3基团，研究了折叠UBI的表面电荷和疏水性影响与SDS（浓度低于CMC）结合的能力。根据CE，赖氨酸残基的乙酰化抑制了11 SDS（[SDS] < 2 mM）的结合，并减少了在SDS中UBI-（NHAc）8解折叠途径上形成的UBI-（NHAc）8·SDSn复合物的数量。比较在0 mM和1 mM SDS下的15 N-1H HSQC光谱与折叠UBI的计算静电表面电位（例如，然而，非线性Poisson-Boltzmann（PB）方程的解）表明，SDS优先在形式上中性的疏水残基（即，Leu和Ile），但具有正静电表面电位（如从非线性Poisson-Boltzmann方程的解预测的）; SDS不与具有形式正电荷的残基均匀地相互作用（例如，Lys或Arg）。因此，阳离子官能团促进SDS与折叠UBI的结合，因为这些基团对正静电表面电位（其延伸超过其自身的货车德瓦尔半径，如PB理论所预测的）产生长程效应，而不是因为阳离子基团必然是与硫酸根基团的离子相互作用的位点。此外，SDS与天然UBI中的残基相关，而不考虑其在α-螺旋或β-折叠结构中的位置（尽管氢键环中的残基不结合SDS）。没有相关性之间的关联的氨基酸与SDS和溶剂可及性的残留物或其酰胺H/D交换率。这项研究建立了几个（也许是几个）因素，控制多个阴离子两亲分子的同时分子识别的折叠胞质蛋白。
A previous study, using capillary electrophoresis (CE), reported that six discrete complexes of ubiquitin (UBI) and sodium dodecyl sulfate (SDS) form at different concentrations of SDS along the pathway to unfolding of UBI in solutions of SDS. One complex (which formed between 0.8 and 1.8 mM SDS) consisted of native UBI associated with approximately 11 molecules of SDS. The current study used CE and 15N/13C-1H heteronuclear single quantum coherence (HSQC) NMR spectroscopy to identify residues in folded UBI that associate specifically with SDS at 0.8-1.8 mM SDS, and to correlate these associations with established biophysical and structural properties of this well-characterized protein. The ability of the surface charge and hydrophobicity of folded UBI to affect the association with SDS (at concentrations below the CMC) was studied, using CE, by converting lys-ε-NH3+ to lys-ε-NHCOCH3 groups. According to CE, the acetylation of lysine residues inhibited the binding of 11 SDS ([SDS] < 2 mM) and decreased the number of complexes of composition UBI-(NHAc)8·SDSn that formed on the pathway of unfolding of UBI-(NHAc)8 in SDS. A comparison of 15N-1H HSQC spectra at 0 mM and 1 mM SDS with calculated electrostatic surface potentials of folded UBI (e.g., solutions to the non-linear Poisson-Boltzmann (PB) equation) suggested, however, that SDS binds preferentially to native UBI at hydrophobic residues that are formally neutral (i.e., Leu and Ile), but that have positive electrostatic surface potential (as predicted from solutions to non-linear Poisson-Boltzmann equations); SDS did not uniformly interact with residues that have formal positive charge (e.g., Lys or Arg). Cationic functional groups, therefore, promote the binding of SDS to folded UBI because these groups exert long-range effects on the positive electrostatic surface potential (which extend beyond their own van der Waal’s radii, as predicted from PB theory), and not because cationic groups are necessarily the site of ionic interactions with sulfate groups. Moreover, SDS associated with residues in native UBI without regard to their location in α-helix or β-sheet structure (although residues in hydrogen-bonded loops did not bind SDS). No correlation was observed between the association of an amino acid with SDS and the solvent accessibility of the residue or its rate of amide H/D exchange. This study establishes a few (of perhaps several) factors that control the simultaneous molecular recognition of multiple anionic amphiphiles by a folded cytosolic protein.
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