Fahmy Karim, Merroun Mohamed, Pollmann Katrin, Raff Johannes, Savchuk Olesya, Hennig Christoph, Selenska-Pobell Sonja
Division of Biophysics, Institute of Nuclear and Hadron Physics, Forschungszentrum Rossendorf, PF 510119, 01314 Dresden, Germany.
Biophys J. 2006 Aug 1;91(3):996-1007. doi: 10.1529/biophysj.105.079137. Epub 2006 May 12.
The S-layer of Bacillus sphaericus strain JG-A12, isolated from a uranium-mining site, exhibits a high metal-binding capacity, indicating that it may provide a protective function by preventing the cellular uptake of heavy metals and radionuclides. This property has allowed the use of this and other S-layers as self-assembling organic templates for the synthesis of nanosized heavy metal cluster arrays. However, little is known about the molecular basis of the metal-protein interactions and their impact on secondary structure. We have studied the secondary structure, protein stability, and Pd((II)) coordination in S-layers from the B. sphaericus strains JG-A12 and NCTC 9602 to elucidate the molecular basis of their biological function and of the metal nanocluster growth. Fourier transform infrared spectroscopy reveals similar secondary structures, containing approximately 35% beta-sheets and little helical structure. pH-induced infrared absorption changes of the side-chain carboxylates evidence a remarkably low pK < 3 in both strains and a structural stabilization when Pd((II)) is bound. The COO(-)-stretching absorptions reveal a predominant Pd((II)) coordination by chelation/bridging by Asp and Glu residues. This agrees with XANES and EXAFS data revealing oxygens as coordinating atoms to Pd((II)). The additional participation of nitrogen is assigned to side chains rather than to the peptide backbone. The topology of nitrogen- and carboxyl-bearing side chains appears to mediate heavy metal binding to the large number of Asp and Glu in both S-layers at particularly low pH as an adaptation to the environment from which the strain JG-A12 has been isolated. These side chains are thus prime targets for the design of engineered S-layer-based nanoclusters.
从铀矿开采现场分离出的球形芽孢杆菌菌株JG-A12的S层具有很高的金属结合能力，这表明它可能通过阻止细胞摄取重金属和放射性核素发挥保护作用。这一特性使得该S层及其他S层可作为自组装有机模板用于合成纳米级重金属簇阵列。然而，对于金属-蛋白质相互作用的分子基础及其对二级结构的影响却知之甚少。我们研究了球形芽孢杆菌菌株JG-A12和NCTC 9602的S层的二级结构、蛋白质稳定性和Pd(II)配位情况，以阐明其生物学功能和金属纳米簇生长的分子基础。傅里叶变换红外光谱显示出相似的二级结构，约含35%的β-折叠且几乎没有螺旋结构。pH诱导的侧链羧酸盐红外吸收变化表明，两种菌株的pK均显著低于3，且结合Pd(II)时结构会稳定。COO-伸缩吸收显示，Asp和Glu残基通过螯合/桥连作用实现主要的Pd(II)配位。这与XANES和EXAFS数据一致，这些数据表明氧是与Pd(II)配位的原子。氮的额外参与归因于侧链而非肽主链。含氮和羧基侧链的拓扑结构似乎在极低pH下介导重金属与两种S层中大量Asp和Glu的结合，这是对菌株JG-A12所分离环境的一种适应。因此，这些侧链是设计基于S层的工程纳米簇的主要靶点。
