SCAN:Role, evolution, and biosynthesis of di-myo-inositol-phosphate

ITQB SCAN Seminar

Title: Role, evolution, and biosynthesis of di-myo-inositol-phosphate in hyperthermophiles

Speaker: Nuno Borges

From: Cell Physiology and NMR Laboratory

Abstract:

Many marine (hyper)thermophiles accumulate compatible solutes not only in response to osmotic stress but also in response to heat stress. Most of these solutes have not been found or are rarely encountered in mesophiles [1]. The best example is di myo inositol phosphate (DIP), which has been found in members of nearly all marine hyperthermophiles, both Bacteria and Archaea, and also in a few thermophiles. In general, the level of DIP increases remarkably at supra-optimal temperature, leading to the assumption that this solute plays a role in adaptation of (hyper)thermophiles to heat stress. However, a definite proof of the physiological function of DIP is lacking.
The biosynthetic pathway of DIP was established by our team [2]. Inositol-1-phosphate cytidylyltransferase (IPCT) catalyses the activation of inositol-1-phosphate into CDP inositol, which is then condensed with another molecule of inositol-1-phosphate to yield di myo inositol phosphate phosphate (DIPP) by the action of DIPP synthase (DIPPS). Finally, DIPP is dephosphorylated into di myo inositol phosphate by a phosphatase. IPCT and DIPPS homologues were found in every organism known to accumulate DIP with the genome sequenced. In most of them, the two activities (IPCT and DIPPS) are present in a single polypeptide chain, while in a few organisms the two activities are encoded by separate genes [3-4]. Functional and structural properties of the bifunctional IPCT/DIPPS enzyme from Archaeoglobus fulgidus will be presented. To obtain insight into the origin and evolution of DIP synthesis, a phylogenetic analysis of the DIP biosynthetic enzymes was performed [5]. In comparison with the 16S rRNA-based phylogenetic tree, significant topology differences were observed in the IPCT/DIPPS-based tree, suggesting the occurrence of multiple horizontal gene transfer events. To determine the physiological role of DIP, a Thermococcus kodakarensis mutant was constructed by deleting the gene encoding the key-enzyme implicated in DIP synthesis. Surprisingly, the DIP deficient mutant and the parental strain exhibited the same growth rate under heat stress [4]. Analysis of the solute pools revealed that the DIP-deficient strain substituted the missing DIP by aspartate, another negatively charged solute. Therefore, we conclude that DIP is part of the global strategy used by Thermococcus kodakarensis to cope with heat stress.

[1] Santos et al., (2011) In Extremophiles Handbook. 4:497-520.
[2] Rodrigues et al., (2007) J. Bacteriol. 189:5405-12.
[3] Rodionov et al., (2007) PNAS 104:4279-84.
[4] Borges et al., (2010) J. Bacteriol. 192:191-7.
[5] Gonçalves et al., (2011) Environ Microbiol. In press.