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Title: Heterotrophic origin and diverse sources of branched glycerol monoalkyl glycerol tetraethers (brGMGTs) in peats and lignites
Award ID(s):
1843285 1702262
Author(s) / Creator(s):
; ; ; ;
Date Published:
Journal Name:
Organic Geochemistry
Page Range / eLocation ID:
Medium: X
Sponsoring Org:
National Science Foundation
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  1. AQP7 is one of the four human aquaglyceroporins that facilitate glycerol transport across the cell membrane, a biophysical process that is essential in human physiology. Therefore, it is interesting to compute AQP7's affinity for its substrate (glycerol) with reasonable certainty to compare with the experimental data suggesting high affinity in contrast with most computational studies predicting low affinity. In this study aimed at computing the AQP7-glycerol affinity with high confidence, we implemented a direct computation of the affinity from unbiased equilibrium molecular dynamics (MD) simulations of three all-atom systems constituted with 0.16 M, 4.32 M, and 10.23 M atoms, respectively. These three sets of simulations manifested a fundamental physics law that the intrinsic fluctuations of pressure in a system are inversely proportional to the system size (the number of atoms in it). These simulations showed that the computed values of glycerol-AQP7 affinity are dependent upon the system size (the inverse affinity estimations were, respectively, 47.3 mM, 1.6 mM, and 0.92 mM for the three model systems). In this, we obtained a lower bound for the AQP7-glycerol affinity (an upper bound for the dissociation constant). Namely, the AQP7-glycerol affinity is stronger than 1087/M (the dissociation constant is less than 0.92 mM). Additionally, we conducted hyper steered MD (hSMD) simulations to map out the Gibbs free-energy profile. From the free-energy profile, we produced an independent computation of the AQP7-glycerol dissociation constant being approximately 0.18 mM. 
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  2. Summary

    Understanding the unique features of algal metabolism may be necessary to realize the full potential of algae as feedstock for the production of biofuels and biomaterials. Under nitrogen deprivation, the green algaC. reinhardtiishowed substantial triacylglycerol (TAG) accumulation and up‐regulation of a gene,GPD2, encoding a multidomain enzyme with a putative phosphoserine phosphatase (PSP) motif fused to glycerol‐3‐phosphate dehydrogenase (GPD) domains. CanonicalGPDenzymes catalyze the synthesis of glycerol‐3‐phosphate (G3P) by reduction of dihydroxyacetone phosphate (DHAP). G3P forms the backbone ofTAGs and membrane glycerolipids and it can be dephosphorylated to yield glycerol, an osmotic stabilizer and compatible solute under hypertonic stress. RecombinantChlamydomonasGPD2 showed both reductase and phosphatase activitiesin vitroand it can work as a bifunctional enzyme capable of synthesizing glycerol directly fromDHAP. In addition,GPD2and a gene encoding glycerol kinase were up‐regulated inChlamydomonascells exposed to high salinity.RNA‐mediated silencing ofGPD2revealed that the multidomain enzyme was required forTAGaccumulation under nitrogen deprivation and for glycerol synthesis under high salinity. Moreover, aGPD2‐mCherry fusion protein was found to localize to the chloroplast, supporting the existence of aGPD2‐dependent plastid pathway for the rapid synthesis of glycerol in response to hyperosmotic stress. We hypothesize that the reductase and phosphatase activities ofPSPGPDmultidomain enzymes may be modulated by post‐translational modifications/mechanisms, allowing them to synthesize primarily G3P or glycerol depending on environmental conditions and/or metabolic demands in algal species of the core Chlorophytes.

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