Bird Scott M, Rawlings Andrea E, Galloway Johanna M, Staniland Sarah S
University of Sheffield, Department of Chemistry, Dainton Building, Sheffield, S3 7HF, UK. Email:
University of Bristol, School of Chemistry, Cantock's Close, Bristol, BS8 1TS, UK.
RSC Adv. 2016 Jan 29;6(9):7356-7363. doi: 10.1039/c5ra16469a. Epub 2016 Jan 19.
Magnetotactic bacteria are able to synthesise precise nanoparticles of the iron oxide magnetite within their cells. These particles are formed in dedicated organelles termed magnetosomes. These lipid membrane compartments use a range of biomineralisation proteins to nucleate and regulate the magnetite crystallisation process. A key component is the membrane protein Mms6, which binds to iron ions and helps to control the formation of the inorganic core. We have previously used Mms6 on gold surfaces patterned with a self-assembled monolayer to successfully produce arrays of magnetic nanoparticles. Here we use this surface system as a mimic of the interior face of the magnetosome membrane to study differences between intact Mms6 and the acid-rich C-terminal peptide subregion of the Mms6 protein. When immobilised on surfaces, the peptide is unable to reproduce the particle size or homogeneity control exhibited by the full Mms6 protein in our experimental setup. Moreover, the peptide is unable to support anchoring of a dense array of nanoparticles to the surface. This system also allows us to deconvolute particle binding from particle nucleation, and shows that Mms6 particle binding is less efficient when supplied with preformed magnetite nanoparticles when compared to particles precipitated from solution in the presence of the surface immobilised Mms6. This suggests that Mms6 binds to iron ions rather than to magnetite surfaces in our system, and is perhaps a nucleating agent rather than a controller of magnetite crystal growth. The comparison between the peptide and the protein under identical experimental conditions indicates that the full length sequence is required to support the full function of Mms6 on surfaces.
趋磁细菌能够在其细胞内合成精确的氧化铁磁铁矿纳米颗粒。这些颗粒在称为磁小体的特定细胞器中形成。这些脂质膜隔室利用一系列生物矿化蛋白来成核并调节磁铁矿的结晶过程。一个关键成分是膜蛋白Mms6，它与铁离子结合并有助于控制无机核心的形成。我们之前在由自组装单分子层图案化的金表面上使用Mms6，成功地制备了磁性纳米颗粒阵列。在这里，我们使用这个表面系统来模拟磁小体膜的内表面，以研究完整的Mms6与Mms6蛋白富含酸性的C末端肽亚区域之间的差异。当固定在表面上时，该肽在我们的实验装置中无法重现完整Mms6蛋白所表现出的颗粒大小或均匀性控制。此外，该肽无法支持密集的纳米颗粒阵列锚定在表面上。这个系统还使我们能够区分颗粒结合与颗粒成核，并表明与在存在表面固定的Mms6的情况下从溶液中沉淀的颗粒相比，当提供预先形成的磁铁矿纳米颗粒时，Mms6颗粒结合效率较低。这表明在我们的系统中Mms6与铁离子结合而不是与磁铁矿表面结合，并且它可能是一种成核剂而不是磁铁矿晶体生长的控制器。在相同实验条件下肽与蛋白质之间的比较表明，需要全长序列来支持Mms6在表面上的完整功能。
