The intracellular interplay between galectin-1 and FGF12 in the assembly of ribosome biogenesis complex.

Galectins constitute a class of lectins that specifically interact with ß-galactoside sugars in glycoconjugates and are implicated in diverse cellular processes, including transport, autophagy or signaling. Since most of the activity of galectins depends on their ability to bind sugar chains, galectins exert their functions mainly in the extracellular space or at the cell surface, which are microenvironments highly enriched in glycoconjugates. Galectins are also abundant inside cells, but their specific intracellular functions are largely unknown. Here we report that galectin-1, -3, -7 and -8 directly interact with the proteinaceous core of fibroblast growth factor 12 (FGF12) in the cytosol and in nucleus. We demonstrate that binding of galectin-1 to FGF12 in the cytosol blocks FGF12 secretion. Furthermore, we show that intracellular galectin-1 affects the assembly of FGF12-containing nuclear/nucleolar ribosome biogenesis complexes consisting of NOLC1 and TCOF1. Our data provide a new link between galectins and FGF proteins, revealing an unexpected glycosylation-independent intracellular interplay between these groups of proteins.

Calcium carbonate polymorph selection in fish otoliths: A key role of phosphorylation of Starmaker-like protein.

Fish otoliths are calcium carbonate biominerals found in the inner ear commonly used for tracking fish biochronologies and as a model system for biomineralization. The process of fish otolith formation is biologically controlled by numerous biomacromolecules which not only affect crystal size, shape, mechanical properties, but also selection of calcium carbonate polymorph (e.g., aragonite, vaterite). The proteinaceous control over calcium carbonate polymorph selection occurs in many other species (e.g., corals, mollusks, echinoderms) but the exact mechanism of protein interactions with calcium and carbonate ions - constituents of CaCO3 - are not fully elucidated. Herein, we focus on a native Starmaker-like protein isolated from vaterite asteriscus otoliths from Cyprinus carpio. The proteomic studies show the presence of the phosphorylated protein in vaterite otoliths. In a series of in vitro mineralization experiments with Starmaker-like, we show that native phosphorylation is a crucial determinant for the selection of a crystal's polymorphic form. This is the first report showing that the switch in calcium carbonate phase depends on the phosphorylation pattern of a single isolated protein. STATEMENT OF SIGNIFICANCE: Calcium carbonate has numerous applications in industry and medicine. However, we still do not understand the mechanism of biologically driven polymorph selection which results in specific biomineral properties. Previous work on calcium carbonate biominerals showed that either several macromolecular factors or high magnesium concentration (non-physiological) are required for proper polymorph selection (e.g., in mollusk shells, corals and otoliths). In this work, we showed for the first time that protein phosphorylation is a crucial factor for controlling the calcium carbonate crystal phase. This is important because a single protein from the otolith organic matrix could switch between polymorphs depending on the phosphorylation level. It seems that protein post-translational modifications (native, not artificial) are more important for biomolecular control of crystal growth than previously considered.

Otolin-1, an otolith- and otoconia-related protein, controls calcium carbonate bioinspired mineralization.

BACKGROUND: Otoliths and otoconia are calcium carbonate biomineral structures that form in the inner ear of fish and humans, respectively. The formation of these structures is tightly linked to the formation of an organic matrix framework with otolin-1, a short collagen-like protein from the C1q family as one of its major constituents. METHODS: In this study, we examined the activity of recombinant otolin-1 originating from Danio rerio and Homo sapiens on calcium carbonate bioinspired mineralization with slow-diffusion method and performed crystals characterization with scanning electron microscopy, two-photon excited fluorescence microscopy, confocal laser scanning microscopy and micro-Raman spectroscopy. RESULTS: We show that both proteins are embedded in the core of CaCO3 crystals that form through the slow-diffusion mineralization method. Both of them influence the morphology but do not change the polymorphic mineral phase. D.rerio otolin-1 also closely adheres to the crystal surface. GENERAL SIGNIFICANCE: The results suggest, that otolin-1 is not a passive scaffold, but is directly involved in regulating the morphology of the resulting calcium carbonate biocrystals.

In vivo and in vitro analysis of starmaker activity in zebrafish otolith biomineralization.

Otoliths are one of the biominerals whose formation is highly controlled by proteins. The first protein discovered to be involved in otolith biomineralization in zebrafish was starmaker (Stm). Previously, Stm was shown to be responsible for the preferential formation of aragonite, a polymorph of calcium carbonate, in otoliths. In this work, proteomic analysis of adult zebrafish otoliths was performed. Stm is the only highly phosphorylated protein found in our studies. Besides previously studied otolith proteins, we discovered several dozens of unknown proteins that reveal the likely mechanism of biomineralization. A comparison of aragonite and vaterite otoliths showed similarities in protein composition. We observed the presence of Stm in both types of otoliths. In vitro studies of 2 characteristic Stm fragments indicated that the DS-rich region has a special biomineralization activity, especially after phosphorylation.-Kalka, M., Markiewicz, N., Ptak, M., Sone, E. D., Ozyhar, A., Dobryszycki, P., Wojtas, M. In vivo and in vitro analysis of starmaker activity in zebrafish otolith biomineralization.