Structural highlights
FunctionPublication Abstract from PubMedPrecisely defined protein aggregates, as exemplified by crystals, have applications in functional materials. Consequently, engineered protein assembly is a rapidly growing field. Anionic calix[n]arenes are useful scaffolds that can mold to cationic proteins and induce oligomerization and assembly. Here, we describe protein-calixarene composites obtained via cocrystallization of commercially available sulfonato-calix[8]arene (sclx8) with the symmetric and "neutral" protein RSL. Cocrystallization occurred across a wide range of conditions and protein charge states, from pH 2.2-9.5, resulting in three crystal forms. Cationization of the protein surface at pH approximately 4 drives calixarene complexation and yielded two types of porous frameworks with pore diameters >3 nm. Both types of framework provide evidence of protein encapsulation by the calixarene. Calixarene-masked proteins act as nodes within the frameworks, displaying octahedral-type coordination in one case. The other framework formed millimeter-scale crystals within hours, without the need for precipitants or specialized equipment. NMR experiments revealed macrocycle-modulated side chain pKa values and suggested a mechanism for pH-triggered assembly. The same low pH framework was generated at high pH with a permanently cationic arginine-enriched RSL variant. Finally, in addition to protein framework fabrication, sclx8 enables de novo structure determination. Facile Fabrication of Protein-Macrocycle Frameworks.,Ramberg KO, Engilberge S, Skorek T, Crowley PB J Am Chem Soc. 2021 Feb 3;143(4):1896-1907. doi: 10.1021/jacs.0c10697. Epub 2021 , Jan 20. PMID:33470808[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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