Search bioRxiv⌕ Search
Home/Archive/bioRxiv

bioRxiv · 10.1101/2020.04.24.058297

Effect of salinity on modulation by ATP, protein kinases and FXYD2 peptide of gill (Na+, K+)-ATPase activity in the swamp ghost crab Ucides cordatus (Brachyura, Ocypodidae)

McNamara, J. C.·Leone, F. A.·Lucena, M. N.·Fabri, L. M.·Garcon, D. P.·Fontes, C. F.·Faleiros, R. O.·Moraes, C. M.
View original source ↗Export metadata ↓

Abstract

The gill (Na+, K+)-ATPase is the main enzyme that underpins osmoregulatory ability in crustaceans that occupy biotopes like mangroves, characterized by salinity variation. We evaluated osmotic and ionic regulatory ability in the semi-terrestrial mangrove crab Ucides cordatus after 10-days acclimation to different salinities. We also analyzed modulation by exogenous FXYD2 peptide and by endogenous protein kinases A and C, and Ca2+- calmodulin-dependent kinase of (Na+, K+)-ATPase activity. Hemolymph osmolality was strongly hyper-/hypo-regulated in crabs acclimated at 2 to 35 {per thousand}S. Cl- was well hyper-/hypo- regulated although Na+ much less so, becoming iso-natremic at high salinity. (Na+, K+)- ATPase activity was greatest in isosmotic crabs (26 {per thousand}S), diminishing progressively from 18 and 8 {per thousand}S ({approx}0.5 fold) to 2 {per thousand}S (0.04-fold), and decreasing notably at 35 {per thousand}S (0.07-fold). At low salinity, the (Na+, K+)-ATPase exhibited a low affinity ATP-binding site that showed Michaelis-Menten behavior. Above 18 {per thousand}S, an additional, high affinity ATP-binding site, corresponding to 10-20% of total (Na+, K+)-ATPase activity appeared. Activity is stimulated by exogenous pig kidney FXYD2 peptide, while endogenous protein kinases A and C and Ca2+/calmodulin-dependent kinase all inhibit activity. This is the first demonstration of inhibitory phosphorylation of a crustacean (Na+, K+)-ATPase by Ca2+/calmodulin-dependent kinase. Curiously, hyper-osmoregulation in U. cordatus shows little dependence on gill (Na+, K+)-ATPase activity, suggesting a role for other ion transporters. These findings reveal that the salinity acclimation response in U. cordatus consists of a suite of osmoregulatory and enzymatic adjustments that maintain its osmotic homeostasis in a challenging, mangrove forest environment. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=138 HEIGHT=200 SRC="FIGDIR/small/058297v1_ufig1.gif" ALT="Figure 1"> View larger version (69K): org.highwire.dtl.DTLVardef@19a35f2org.highwire.dtl.DTLVardef@14bd0d3org.highwire.dtl.DTLVardef@7adaa5org.highwire.dtl.DTLVardef@1a88e10_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIGill (Na+, K+)-ATPase activity is greatest in isosmotic crabs, diminishing in lower and higher salinities. C_LIO_LIA high affinity ATP-binding site (10-20% of total activity) is exposed above 18 {per thousand}S. C_LIO_LIExogenous FXYD2 peptide stimulates activity; endogenous PKA, PKC and CaMK inhibit activity. C_LIO_LIFirst demonstration of inhibitory phosphorylation of crustacean (Na+, K+)-ATPase by CaMK. C_LIO_LIHyper-osmoregulation shows little dependence on (Na+, K+)-ATPase activity. C_LI

Source connections

Explore related subjects

biochemistryPreprint

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

McNamara, J. C., Leone, F. A., Lucena, M. N., Fabri, L. M., Garcon, D. P., Fontes, C. F., Faleiros, R. O., Moraes, C. M.. 2020-04-25. Effect of salinity on modulation by ATP, protein kinases and FXYD2 peptide of gill (Na+, K+)-ATPase activity in the swamp ghost crab Ucides cordatus (Brachyura, Ocypodidae). https://doi.org/10.1101/2020.04.24.058297

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related preprints

bioRxiv2026

Hierarchical cysteine oxidation controls reversible amyloid formation in an ankyrin repeat protein

The formation of amyloids, including functional amyloids, is observed for an increasing number of proteins but the molecular mechanisms that control this structural transition remain poorly understood. Here we report that the kinase inhibitor protein P18 (drP18) from Danio rerio (zebrafish), which contains two cysteine residues, undergoes a complex and hierarchical redox switch that strictly governs reversible amyloid formation. We identify cysteine 50 (C50) acting as a regulatory residue. Upon oxidation, C50 forms an intramolecular disulfide bond with the executioner cysteine 128 (C128), thereby blocking it. C50 can become S-glutathionylated, and upon oxidation, C128 then forms intermolecular disulfides that lead to rapid transition into amyloid fibrils. S-glutathionylation of C50 therefore enables amyloid formation of drP18 and the outcome is oxidant-dependent with diamide, hydrogen peroxide, peroxymonocarbonate and hypothiocyanous acid each leading to amyloid assembly with distinct kinetics and morphologies. These amyloids are fully reversible, where disulfide reduction is leading to disassembly. Whereas monomeric drP18 inhibits CDK4-mediated retinoblastoma phosphorylation, the amyloid conformation abolishes this inhibition, and reduction restores both structure and function. Expression of drP18 in zebrafish embryos yields Congo red-positive, oxidation-dependent aggregates in vivo. Together, our findings show that a regulatory cysteine controls an executioner cysteine to induce reversible, functional amyloid formation, revealing that proteins can encode sophisticated mechanisms to control amyloid assembly.

biochemistry↗
bioRxiv2026

Snapshots from the Catalytic Landscape of Chalcone Isomerase

Chalcone isomerase (CHI) catalyzes the cyclization of 3-ring scaffolds of flavonoids, a class of plant-based natural products important for nutrition and disease prevention. A persistent question has been whether the enzyme uses dynamics to facilitate conformational rearrangements of substrates within the active site. To help resolve this question, CHI was crystallized with phloretin, a flexible substrate analogue that cannot undergo cyclization. The crystal structure possesses eight protein molecules per asymmetric unit, revealing different active site conformations that accommodate different bound conformers of phloretin. Together, the structural snapshots depict a series of coordinated, dynamic chemical interactions that lower barriers to substrate rearrangements approaching bond formation. Differential scanning fluorimetry combined with mutational analysis and enzyme kinetics further confirm that phloretin binds to the enzyme active site and that it acts as a competitive inhibitor of CHI. Together these findings answer outstanding questions about the flexibility and dynamics of CHI catalysis, information that may be useful for future biosynthetic design and enzyme engineering goals. Overall, this work supports a catalytic model in which the CHI enzyme operates as a dynamic ensemble of structures necessary to facilitate catalytic substrate rearrangements.

biochemistry↗
bioRxiv2026

Structures of pUG-fold RNA bound to DNMT1 reveal a mechanism for RNA-mediated epigenetic regulation

Many chromatin-associated proteins have been found to bind RNA as a means of epigenetic regulation. Specifically, DNA methyltransferase 1 (DNMT1), which maintains cytosine methylation at CpG dinucleotides, is inhibited by RNA at transcribed DNA loci in cells. However, the mechanisms by which RNA binds DNMT1 and inhibits its activity remain unknown. Here, we determine a series of cryogenic electron microscopy (cryo-EM) structures of human DNMT1 bound to pUG-fold RNA, a non-canonical G-quadruplex previously observed to inhibit activity, revealing two distinct RNA-binding modes. The pUG-fold RNA binds the surface of DNMT1 in its autoinhibited conformation across a positively charged surface between the methyltransferase domain and the CXXC domain, and it binds directly in the active site of an open DNMT1 conformation. RNA binding is sterically incompatible with substrate DNA engagement in both states. Our 2.5 [A] structure captures the intricate network of hydrogen bonds and electrostatic interactions between amino acids in the methyltransferase domain and the tetrad layers of pUG-fold RNA. Metadynamics molecular dynamics simulations provide an orthogonal view of the conformational landscape of DNMT1, revealing the two distinct RNA-binding modes. Furthermore, our analysis of published DNMT1 RIP-seq and eCLIP-seq data confirms that DNMT1-interacting RNAs in cells exhibit a strong propensity to form non-canonical G-quadruplex RNA structures. Collectively, our study provides the first structural basis for pUG-fold RNA recognition by a protein and illustrates how cryo-EM and AI-based methods for protein and RNA structure prediction synergize to inform the mechanism of RNA-mediated regulation of DNMT1.

biochemistry↗