Arginine kinase in the demosponge Suberites domuncula:regulation of its expression and catalytic activity by silicic acid

Abstract

SUMMARY In Demospongiae (phylum Porifera) the formation of the siliceous skeleton,composed of spicules, is an energetically expensive reaction. The present study demonstrates that primmorphs from the demosponge Suberites domuncula express the gene for arginine kinase after exposure to exogenous silicic acid. The deduced sponge arginine kinase sequence displays the two characteristic domains of the ATP:guanido phosphotransferases; it can be grouped to the `usual' mono-domain 40 kDa guanidino kinases (arginine kinases). Phylogenetic studies indicate that the metazoan guanidino kinases evolved from this ancestral sponge enzyme; among them are also the `unusual'two-domain 80 kDa guanidino kinases. The high expression level of the arginine kinase gene was already measurable 1 day after addition of silicic acid by northern blot, as well as by in situ hybridization analysis. Parallel determinations of enzyme activity confirmed that high levels of arginine kinase are present in primmorphs that had been exposed for 1-5 days to silicic acid. Finally, transmission electron-microscopical studies showed that primmorphs containing high levels of arginine kinase also produce siliceous spicules. These data highlight that silicic acid is an inorganic morphogenetic factor that induces the expression of the arginine kinase, which in turn probably catalyzes the reversible transfer of high-energy phosphoryl groups.

ATP distribution and localization of mitochondria in Suberites domuncula (Olivi 1792) tissue

“…AK is the crucial enzyme in energy-demanding reactions of spicule formation in primmorphs (Perovic-Ottstadt et al, 2005). The phosphagen kinases are localized at the sites of ATP synthesis and hydrolysis, enabling a tuned regulation of the intracellular phosphate concentration (Ellington, 2001).…”

“…To remove the typical sponge color, the sections were treated with different concentrations of ethanol. After rehydration, sections were hybridized overnight at 40°C [23 sodium chloride-sodium citrate buffer (SSC), 50% formamide] with DIG-labeled probe, a 250nt Suberites domuncula arginine kinase (SDAK) cDNA portion (Perovic-Ottstadt et al, 2005). The sections were washed at 45°C in 23 SSC and 0.23 SSC.…”

“…DNA oligonucleotide probes were constructed as described previously (Perovic-Ottstadt et al, 2005). Antisense and sense ssDNA DIG-labeled probes were synthesized by PCR using the PCR-DIG-Probe-Synthesis Kit (Roche) according to the manufacturer's protocol.…”

“…As in most eukaryotic cells, the main source of adenosine triphosphate (ATP) in sponges is generated by mitochondrial oxidative phosphorylation (Sona et al, 2004). The highest energy consumption should be localized in choanocytes, which are the 'motor' cells that drive the water through the aqueous channel system (Perovic-Ottstadt et al, 2005). The choanocytes of sponges are structurally and functionally identical to choanoflagellates, which facilitated speculations about the evolutionary relationship between the two groups (Barnes, 1987).…”

Deep ocean nutrients during the Last Glacial Maximum deduced from sponge silicon isotopic compositions

“…Alternatively, Si(OH) 4 availability may control the internal #+&" biochemical pathways involved during silicification, which may in turn determine isotopic #+'" fractionation. For example, ambient Si(OH) 4 is a known modulating factor that regulates #+(" the expression of silicatein and silicase, and induces expression of genes for other enzymes #+)" involved in biosilicification (Perovic-Ottstadt et al, 2005;Müller et al, 2007). Further #+*" work is required to understand the biosilicification process and, in particular, the reactions #!+" that result in isotopic fractionation.…”