Polymorphic forms of cilostazol

Two unique conformational polymorphic forms of the compound 6‐[4‐(1‐cyclo­hexyl‐1H‐tetrazol‐5‐yl)­butoxy]‐3,4‐di­hydro­quinolin‐2(1H)‐one (cilostazol), C₂₀H₂₇N₅O₂, have been discovered and characterized using single‐crystal X‐ray structural analysis. A third polymorph also exists, but acceptable crystals could not be obtained. Features of both reported polymorphic structures include a chair conformation of the cyclo­hexyl ring and puckering in the quinolinone ring. The major feature distinguishing the two polymorphic forms is a rotational twisting of the butoxy chain between the tetrazole and quinolinone rings. This difference in conformation influences the intermolecular forces, and hence the packing of the two mol­ecules during crystallization.     

A role for sulfation-desulfation in the uptake of bisphenol a into breast tumor cells

Bisphenol A (BPA) is a widely used plasticizer whose estrogenic properties may impact hormone-responsive disorders and fetal development. In vivo, BPA appears to have greater activity than is suggested by its estrogen receptor (ER) binding affinity. This may be a result of BPA sulfation/desulfation providing a pathway for selective uptake into hormone-responsive cells. BPA is a substrate for estrogen sulfotransferase, and bisphenol A sulfate (BPAS) and disulfate are substrates for estrone sulfatase. Although the sulfated xenobiotics bind poorly to the ER, both stimulated the growth of receptor-positive breast tumor cells. Treatment of MCF-7 cells with BPAS leads to desulfation and uptake of BPA. No BPAS is found inside the cells. These findings suggest a mechanism for the selective uptake of BPA into cells expressing estrone sulfatase. Therefore, sulfation may increase the estrogenic potential of xenobiotics.     

Design of functional ferritin-like proteins with hydrophobic cavities

Ferritin four-helix bundle subunits self-assemble to create a stable multimer with a large central hydrophilic cavity where metal ions bind. To explore the versatility of this reaction vessel, computational design was used to generate cavities with increasingly apolar surface areas inside a dodecameric ferritin-like protein, Dps. Cavity mutants, in which as many as 120 surface accessible hydrophilic residues were replaced with hydrophobic amino acids, were shown to still assemble properly using size-exclusion chromatography and dynamic light scattering measurements. Wild-type Dps exhibited highly cooperative subunit folding and assembly, which was monitored by changes in Trp fluorescence and UV circular dichroism. The hydrophobic cavity mutants showed distinctly less cooperative unfolding behavior, with one mutant forming a partially assembled intermediate upon guanidine denaturation. Although the stability of Dps to such denaturation decreased with increasing apolar surface area, all proteins exhibited high melting temperatures, T(m) = 74-90 degrees C. Despite the large number of mutations, near-native ability to mineralize iron was maintained. This work illustrates the versatility of the ferritin scaffold for engineering large protein cavities with novel properties.