Oral Presentation Australian & New Zealand Society of Magnetic Resonance Conference 2017

Regulation of skeletal material formation in corals – from functional proteins to whole organism (#64)

GIL Goobes 1 , Rotem Gavriel 1 , Maayan Neder 2 , Anat Akiva 3 , Jonathan Glick 1 , Keren Kahil 3 , Keren Keinan-Adamsky 1 , Tali Mass 2
  1. Bar Ilan University, Ramat Gan, NON-US/CANADA, Israel
  2. Marine Biology, University o Haifa, Haifa, Israel
  3. Structural Biology, Weizmann Institute of Science, Rehovot, Israel

The aragonitic skeleton of hard corals is a sensitive gauge of carbonate concentration in the oceans. With the rise of CO2 levels in the atmosphere and consequent acidification of seawater, adverse effects on coral ecology are already observed. Unlocking the mechanisms of aragonite and amorphous CaCO3 mineralization during coral skeletogenesis is crucial for reversing such detrimental processes [1]. In particular, understanding calcium carbonate precipitation during the early vulnerable stages of the coral development from motile planulae to settled coral polyp is key and not yet investigated. Recently, coral-acidic-residues-rich proteins (CARPs), active in CaCO3 mineralization, were isolated from the hard coral Stylophora pistillata [2]. The details of their regulatory activity are not known. Two approaches are undertaken to examine mineralization in hard corals.

First, the activity of full CARP3 protein and two of its domains in CaCO3 precipitation from seawater-like solutions were monitored through NMR and X-ray and EM techniques. The protein and its peptidyl domains divert spontaneous crystallization from aragonite to magnesium-calcite. They affect the thickness of amorphous CaCO3 layer coating the crystals and their morphology. 13C MAS NMR is used to pinpoint the type of disordered carbonate phases formed with the peptides. 2D 1H-13C HETCOR measurements show that the biomolecules are located in the disordered surface phases. The solution structures of the peptidyl domains measured by NMR and their dissimilar amino acid sequences are discussed in the context of their disparate effect on the CaCO3 minerals precipitated. The effects of these two domains are put together in the integral influence of the entire protein on the material formed.

Second, the whole coral organism, 13C-labeled, was examined in the early stage of planulae and following metamorphosis to the settled polyp stage where skeletal mineralization was though to occur. Using 13C MAS NMR complemented by cryo-SEM with energy dispersive X-ray analysis, we identified mineralization onset prior to coral settling. We showed modulation of ion content in the mineralized tissue from an amorphous calcium carbonate phase [3] to a more ordered aragonite phase accompanied by up- and down-regulation of CARP proteins. Using 13C DARR measurements, the proximity of up-regulated CARP in each stage with the associated carbonate phase is implicated. Glu-rich CARP is localized in disordered carbonate mineral phase in the planulae, whereas Asp-rich CARPS are localized in the ordered aragonitic phase in the settled coral.

  1. Von Euw, S. et al. Biological control of aragonite formation in stony corals. Science 356, 933-938, doi:10.1126/science.aam6371 (2017).
  2. Mass, T. et al. Cloning and characterization of four novel coral acid-rich proteins that precipitate carbonates in vitro. Current biology 23, 1126-1131 (2013).
  3. Reeder, R. J. et al. Characterization of structure in biogenic amorphous calcium carbonate: Pair distribution function and nuclear magnetic resonance studies of lobster gastrolith. Crystal Growth & Design 13, 1905-1914, doi:10.1021/cg301653s (2013).