During eukaryotic ribosome biogenesis, members of the conserved atypical serine/threonine protein kinase family, the RIO kinases (Rio1, Rio2 and Rio3) function in small ribosomal subunit biogenesis. Structural analysis of Rio2 indicated a role as a conformation-sensing ATPase rather than a kinase to regulate its dynamic association with the pre-40S subunit. However, it remained elusive at which step and by which mechanism the other RIO kinase members act. Here, we have determined the crystal structure of the human Rio1–ATP–Mg2+ complex carrying a phosphoaspartate in the active site indicative of ATPase activity. Structure-based mutations in yeast showed that Rio1's catalytic activity regulates its pre-40S association. Furthermore, we provide evidence that Rio1 associates with a very late pre-40S via its conserved C-terminal domain. Moreover, a rio1 dominant-negative mutant defective in ATP hydrolysis induced trapping of late biogenesis factors in pre-ribosomal particles, which turned out not to be pre-40S but 80S-like ribosomes. Thus, the RIO kinase fold generates a versatile ATPase enzyme, which in the case of Rio1 is activated following the Rio2 step to regulate one of the final 40S maturation events, at which time the 60S subunit is recruited for final quality control check.

The steroidogenic acute regulatory protein-related lipid transfer (START) domain family is defined by a conserved 210-amino acid sequence that folds into an α/β helix-grip structure. Members of this protein family bind a variety of ligands, including cholesterol, phospholipids, sphingolipids, and bile acids, with putative roles in nonvesicular lipid transport, metabolism, and cell signaling. Among the soluble START proteins, STARD4 is expressed in most tissues and has previously been shown to transfer sterol, but the molecular mechanisms of membrane interaction and sterol binding remain unclear. In this work, we use biochemical techniques to characterize regions of STARD4 and determine their role in membrane interaction and sterol binding. Our results show that STARD4 interacts with anionic membranes through a surface-exposed basic patch and that introducing a mutation (L124D) into the Omega-1 (Ω1) loop, which covers the sterol binding pocket, attenuates sterol transfer activity. To gain insight into the attenuating mechanism of the L124D mutation, we conducted structural and biophysical studies of wild-type and L124D STARD4. These studies show that the L124D mutation reduces the conformational flexibility of the protein, resulting in a diminished level of membrane interaction and sterol transfer. These studies also reveal that the C-terminal α-helix, and not the Ω1 loop, partitions into the membrane bilayer. On the basis of these observations, we propose a model of STARD4 membrane interaction and sterol binding and release that requires dynamic movement of both the Ω1 loop and membrane insertion of the C-terminal α-helix.

[Structure: see text] A series of organoboron quinolates with emission colors ranging from blue to red have been prepared. In comparison to the respective AlQ3 derivatives a distinct blue-shift of the emission is observed. Theoretical calculations serve to provide insight into the nature of the frontier orbitals and the effect of the substituents in the 5-position of the quinolate ligands on the relative HOMO and LUMO energy levels. An efficient new blue emitting material with a pinacolborane substituent has been identified.

A modular one-pot approach for the synthesis of well-defined organoboron quinolate polymers and the tuning of their photoluminescence is reported. Highly selective borylation of poly(4-trimethylsilylstyrene) (PSSiMe 3 ) followed by replacement of one of the bromine substituents in the resulting reactive polymer PSBBr 2 with tert-butylphenyl groups led to the common intermediate PSBPhBr. A series of organoboron quinolate polymers PSBPhQ were then obtained in high isolated yields (65-85%) by in situ treatment of PSBPhBr with differently substituted 8-hydroxyquinoline derivatives. All the quinolate polymers were fully characterized by multinuclear NMR spectroscopy, elemental analysis, gel permeation chromatography in-line with multiangle laser light scattering (GPC-MALLS), differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA). Luminescence measurements revealed distinct emission bands, ranging from the blue to the red region (486-615 nm), depending on the substitution pattern on the quinolate ligands.