Zsila Ferenc, Juhász Tünde, Bősze Szilvia, Horváti Kata, Beke-Somfai Tamás
Biomolecular Self-Assembly Group, Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Budapest, Hungary.
MTA-ELTE Research Group of Peptide Chemistry, Hungarian Academy of Sciences, Eötvös Loránd University, Budapest, Hungary.
Chirality. 2018 Feb;30(2):195-205. doi: 10.1002/chir.22784. Epub 2017 Nov 7.
The interaction of protoporphyrin compounds of human origin with the major bee venom component melittin (26 a.a., Z +6) and its hybrid derivative (CM15, 15 a.a., Z +6) were studied by a combination of various spectroscopic methods. Throughout a two-state, concentration-dependent process, hemin and its metabolites (biliverdin, bilirubin, bilirubin ditaurate) increase the parallel β-sheet content of the natively unfolded melittin, suggesting the oligomerization of the peptide chains. In contrast, α-helix promoting effect was observed with the also disordered but more cationic CM15. According to fluorescence quenching experiments, the sole Trp residue of melittin is the key player during the binding, in the vicinity of which the first pigment molecule is accommodated presumably making indole-porphyrin π-π stacking interaction. As circular dichroism titration data suggest, cooperative association of additional ligands subsequently occurs, resulting in multimeric complexes with an apparent dissociation constant ranged from 20 to 65 μM. Spectroscopic measurements conducted with the bilirubin catabolite urobilin and stercobilin refer to the requirement of intact dipyrrinone moieties for inducing secondary structure transformations. The binding topography of porphyrin rings on a model parallel β-sheet motif was evaluated by absorption spectroscopy and computational modeling showing a slipped-cofacial binding mode responsible for the red shift and hypochromism of the Soret band. Our results may aid to recognize porphyrin-responsive binding motifs of biologically relevant, intrinsically disordered peptides and proteins, where transient conformations play a vital role in their functions.
通过多种光谱方法相结合，研究了人类来源的原卟啉化合物与主要蜂毒成分蜂毒肽（26个氨基酸，Z +6）及其杂合衍生物（CM15，15个氨基酸，Z +6）之间的相互作用。在一个两态的、浓度依赖性过程中，血红素及其代谢产物（胆绿素、胆红素、胆红素二牛磺酸盐）增加了天然未折叠蜂毒肽的平行β-折叠含量，表明肽链发生了寡聚化。相比之下，对于同样无序但带更多正电荷的CM15，观察到了α-螺旋促进作用。根据荧光猝灭实验，蜂毒肽唯一的色氨酸残基是结合过程中的关键参与者，第一个色素分子可能在其附近形成吲哚-卟啉π-π堆积相互作用。正如圆二色性滴定数据所表明的，随后会发生额外配体的协同缔合，形成表观解离常数范围为20至65 μM的多聚体复合物。用胆红素分解代谢产物尿胆素和粪胆素进行的光谱测量表明，完整的二吡咯酮部分是诱导二级结构转变所必需的。通过吸收光谱和计算建模评估了卟啉环在模型平行β-折叠基序上的结合拓扑结构，结果表明一种错位共面结合模式导致了Soret带的红移和减色。我们的结果可能有助于识别生物学上相关的、内在无序的肽和蛋白质的卟啉响应性结合基序，其中瞬时构象在其功能中起着至关重要的作用。
