myo-Inositol hexakisphosphate is a major component of an extracellular structure in the parasitic cestode Echinococcus granulosus

Abstract

myo-Inositol hexakisphosphate (IP6) is an abundant intracellular component of animal cells. In this study we describe the presence of extracellular IP6 in the hydatid cyst wall (HCW) of the larval stage of the cestode parasite Echinococcus granulosus. The HCW comprises an inner cellular layer and an outer, acellular (laminated) layer up to 2mm in thickness that protects the parasite from host immune cells. A compound, subsequently identified as IP6, was detected in and purified from an HCW extract on the basis of its capacity to inhibit complement activation. The identification of the isolated compound was carried out by a combination of NMR, MS and TLC. The majority of IP6 in the HCW was found in the acellular layer, with only a small fraction of the compound being extracted from cells. In the laminated layer, IP6 was present in association with calcium, and accounted for up to 15% of the total dry mass of the HCW. IP6 was not detected in any other structures or stages of the parasite. Our results imply that IP6 is secreted by the larval stage of the parasite in a polarized fashion towards the interface with the host. This is the first report of the secretion of IP6, and the possible implications beyond the biology of E. granulosus are discussed.

Myo‐inositol hexakisphosphate, isolated from female gametophyte tissue of loblolly pine, inhibits growth of early‐stage somatic embryos

“…Similar observations have been reported by others (Hanakahi et al. , 2000; Irigoin et al. , 2002), and this phenomenon has been studied in detail by Van der Kaay & Van Haastert (1995).…”

Solution behaviour of myo-inositol hexakisphosphate in the presence of multivalent cations. Prediction of a neutral pentamagnesium species under cytosolic/nuclear conditions

“…Whether soluble or bound to fixed components, it is expected that nuclear and cytosolic InsP 6 exist as complexes with Mg(II) and/or Ca(II), but such species have not been defined. InsP 6 is not confined to the nuclear/cytosolic compartments in all eukaryotes [13,14], an observation that extends the possibilities of interactions with Ca(II) in particular. Complexation of Fe(III) by InsP 6 has received particular attention, because it is surprisingly effective at preventing the participation of iron in the redox cycles catalysing the formation of the hydroxyl radical [15][16][17].…”

“…Such species are expected to have exceptionally large hydrated radii. This probably explains the puzzling observation that InsP 6 behaves in neutral solutions (lacking multivalent cations) as a several-kDa species [1,13,36,37]. Table 2 lists the constants for InsP 6 interactions with divalent cations as determined using experimental data in 0.15 M NaClO 4 exclusively; we envisage this set of effective constants to be the most useful one for biological researchers.…”

Characterization ofmyo‐inositol hexakisphosphate deposits from larvalEchinococcus granulosus

“…Similarly, the unsaturated amino acids generated by β‐elimination are hydrolysed, with loss of A 240 nm , and the corresponding data were thus only plotted up to 48 h. Error bars on the insoluble mass and A 240 nm plots represent standard deviations for independent hydrolyses carried out in triplicate. (B) Ins P 6 is retained in the insoluble residue throughout the hydrolysis period as assessed by TLC in [8].…”

“…The results described above made it plausible that the deposits were formed by a single major compound and could thus be assigned a defined stoichiometry. As we had previous evidence that the major counterion of Ins P 6 in the LL was Ca 2+ [8], we chose to compare our purified material with synthetic calcium Ins P 6 . Calcium Ins P 6 prepared under a variety of conditions has the stoichiometry Ca 5 H 2 L·16H 2 O (L being fully deprotonated Ins P 6 ) [13a].…”