The effect of counter ions on the conformation of intrinsically disordered proteins studied by size-exclusion chromatography

Mobile Affinity Sorbent Chromatography

The objective in routine analyses is generally to determine a small number of analytes. With samples containing ∼103 or more components there will be insufficient peak capacity to resolve analytes from nonanalytes. This issue was addressed herein through a new type of separation mechanism in which small groups of targeted analytes are bound with high affinity to a soluble analyte-sequestering transport phase (ASTP) composed of a ∼25 nm Stokes radius hydrophilic polymer core (HPC). When introduced into a 30 nm pore diameter size-exclusion chromatography (SEC) column, ASTP/analyte complexes elute within minutes, together, unretained, and relatively pure in the first chromatographic peak. Nonanalytes, in contrast, enter pore matrices of the packing material, are retarded in elution velocity, and are eluted later, separated from analytes. Fabrication of ASTPs was achieved by covalently coupling an antibody or some other affinity selector to a high molecular weight HPC. Beyond sequestering analytes, the function of ASTPs is to act as a molecular weight shifting agent, conveying an effective molecular weight to analytes that is much larger than that of nonanalytes and causing them to elute in the SEC void volume. This mode of separation is referred to as mobile affinity sorbent chromatography (MASC). Subsequent to their purification, ASTP/analyte complexes were detected by fluorescence spectrometry.

Intrinsically disordered and pliable Starmaker-like protein from medaka (Oryzias latipes) controls the formation of calcium carbonate crystals

Fish otoliths, biominerals composed of calcium carbonate with a small amount of organic matrix, are involved in the functioning of the inner ear. Starmaker (Stm) from zebrafish (Danio rerio) was the first protein found to be capable of controlling the formation of otoliths. Recently, a gene was identified encoding the Starmaker-like (Stm-l) protein from medaka (Oryzias latipes), a putative homologue of Stm and human dentine sialophosphoprotein. Although there is no sequence similarity between Stm-l and Stm, Stm-l was suggested to be involved in the biomineralization of otoliths, as had been observed for Stm even before. The molecular properties and functioning of Stm-l as a putative regulatory protein in otolith formation have not been characterized yet. A comprehensive biochemical and biophysical analysis of recombinant Stm-l, along with in silico examinations, indicated that Stm-l exhibits properties of a coil-like intrinsically disordered protein. Stm-l possesses an elongated and pliable structure that is able to adopt a more ordered and rigid conformation under the influence of different factors. An in vitro assay of the biomineralization activity of Stm-l indicated that Stm-l affected the size, shape and number of calcium carbonate crystals. The functional significance of intrinsically disordered properties of Stm-l and the possible role of this protein in controlling the formation of calcium carbonate crystals is discussed.