Olafson Katy N, Rimer Jeffrey D, Vekilov Peter G
Department of Chemical and Biomolecular Engineering, and Department of Chemistry, University of Houston , Houston, Texas 77204, United States.
Cryst Growth Des. 2014 May 7;14(5):2123-2127. doi: 10.1021/cg5002682. Epub 2014 Apr 7.
Hematin crystallization is an essential component of the physiology of malaria parasites. Several antimalarial drugs are believed to inhibit crystallization and expose the parasites to toxic soluble hematin. Hence, understanding the mechanisms of hematin crystal growth and inhibition is crucial for the design of new drugs. A major obstacle to microscopic, spectroscopic, and crystallographic studies of hematin crystallization has been the unavailability of large hematin crystals grown under conditions representative of the parasite anatomy. We have developed a biomimetic method to reproducibly grow large hematin crystals reaching 50 μm in length. We imitate the digestive vacuole of and employ a two-phase solution of octanol and citric buffer. The nucleation of seeds is enhanced at the interface between the aqueous and organic phases, where an ordered layer of octanol molecules is known to serve as substrate for nucleation. The seeds are transferred to hematin-saturated octanol in contact with citric buffer. We show that the crystals grow in the octanol layer, while the buffer supplies hydrogen ions needed for bonds that link the hematin molecules in the crystal. The availability of large hematin crystals opens new avenues for studies of hematin detoxification of malaria parasites in host erythrocytes.
血红素结晶是疟原虫生理过程的一个重要组成部分。据信，几种抗疟药物可抑制结晶，并使疟原虫暴露于有毒的可溶性血红素中。因此，了解血红素晶体生长和抑制的机制对于新药设计至关重要。血红素结晶的显微镜、光谱和晶体学研究的一个主要障碍是缺乏在代表寄生虫解剖结构的条件下生长的大型血红素晶体。我们开发了一种仿生方法，可重复性地生长出长度达50微米的大型血红素晶体。我们模拟疟原虫的消化液泡，并采用辛醇和柠檬酸缓冲液的两相溶液。在水相和有机相的界面处，种子的成核作用增强，已知有序排列的辛醇分子层可作为成核的底物。将种子转移到与柠檬酸缓冲液接触的血红素饱和辛醇中。我们发现晶体在辛醇层中生长，而缓冲液提供晶体中连接血红素分子的键所需的氢离子。大型血红素晶体的可得性为研究宿主红细胞中疟原虫的血红素解毒开辟了新途径。
