Search bioRxiv⌕ Search
Home/Archive/bioRxiv

bioRxiv · 10.1101/2024.08.16.608318

Functional investigation of a putative calcium-binding site involved in the inhibition of inositol 1,4,5-trisphosphate receptor activity

Arige, V.·Wagner, L. E.·Malik, S.·Baker, M. R.·Fan, G.·Serysheva, I. I.·Yule, D. I.
View original source ↗Export metadata ↓

Abstract

A wide variety of factors influence inositol 1,4,5-trisphosphate (IP3) receptor (IP3R) activity resulting in modulation of intracellular Ca2+ release. This regulation is thought to define the spatio-temporal patterns of Ca2+ signals necessary for the appropriate activation of downstream effectors. The binding of both IP3 and Ca2+ are obligatory for IP3R channel opening, however, Ca2+ regulates IP3R activity in a biphasic manner. Mutational studies have revealed that Ca2+ binding to a high-affinity pocket formed by the ARM3 domain and linker domain promotes IP3R channel opening without altering the Ca2+ dependency for channel inactivation. These data suggest a distinct low-affinity Ca2+ binding site is responsible for the reduction in IP3R activity at higher [Ca2+]. We determined the consequences of mutating a cluster of acidic residues in the ARM2 and central linker domain reported to coordinate Ca2+ in cryo-EM structures of the IP3R type 3. This site is termed the "CD Ca2+ binding site" and is well-conserved in all IP3R sub-types. We show that the CD site Ca2+ binding mutants where the negatively charged glutamic acid residues are mutated to alanine exhibited enhanced sensitivity to IP3-generating agonists. Ca2+ binding mutants displayed spontaneous elemental Ca2+ events (Ca2+ puffs) and the number of IP3-induced Ca2+ puffs was significantly augmented in cells stably expressing Ca2+ binding site mutants. When measured with "on-nucleus" patch clamp, the inhibitory effect of high [Ca2+] on single channel-open probability (Po) was reduced in mutant channels and this effect was dependent on [ATP]. These results indicate that Ca2+ binding to the putative CD Ca2+ inhibitory site facilitates the reduction in IP3R channel activation when cytosolic [ATP] is reduced and suggest that at higher [ATP], additional Ca2+ binding motifs may contribute to the biphasic regulation of IP3-induced Ca2+ release.

Source connections

Explore related subjects

biochemistryPreprint

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Arige, V., Wagner, L. E., Malik, S., Baker, M. R., Fan, G., Serysheva, I. I., Yule, D. I.. 2024-08-17. Functional investigation of a putative calcium-binding site involved in the inhibition of inositol 1,4,5-trisphosphate receptor activity. https://doi.org/10.1101/2024.08.16.608318

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

KEEP EXPLORING

Related preprints

bioRxiv2026

Probing the sequence variability tolerance in a de novo α-helical barrel biocatalyst

De novo-designed enzymes have recently achieved high catalytic activity and stereoselectivity while demonstrating exceptional thermostability in entirely novel protein scaffolds. Among these, -helical barrel protein scaffolds are attractive structures for biocatalysis due to their structural simplicity, high thermostability, and rationalizable sequence patterning. However, enabling major structural reengineering of these scaffolds while maintaining the structure, stability and catalytic activity while also improving soluble protein production remain major challenges and pose the fundamental question how engineerable a de novo backbone-sequence pair is. Here, we combine deep learning based and classic computational protein design to modify and optimize de novo -helical barrel biocatalysts. Using the previously reported six-helical barrel 6H5L as a model scaffold, AlphaFold2-guided RosettaRemodel enabled the design of a truncated variant, whose crystal structure closely matches the design model. Additional sequence-redesign using ProteinMPNN generated a variant with a tenfold increase of soluble protein yield in Escherichia coli. Biochemical, biophysical, and structural analyses showed that both variants retained the overall barrel architecture, high thermal stability, and catalytic activity for both purified protein and whole-cell systems. Detailed kinetic analysis on the variants showed both variation in kcat and Km, reflecting changes in catalytic turnover and substrate binding. Together, these approaches provide new insights and possibilities for the further engineering of functional de novo -helical barrels, their ability to withstand dramatically large sequence changes and their broader application in biocatalysis and biotechnology.

biochemistry↗
bioRxiv2026

Conjunctive Targeting Links Drug Synergy to Emergent Proteome Structural States

Combinatorial therapies are widely used in the treatment of acute myeloid leukemia (AML) to address disease heterogeneity, adaptive resistance, and rewired signaling and metabolic states. Yet drug prioritization remains largely guided by clinical or phenotypic evidence, while the molecular mechanisms underlying effective drug combinations remain incompletely defined. To narrow this gap, we developed Combinatorial high-ratio Partial proteolysis with reference PRoteome Analysis (CoPPRA), a structural proteomics workflow based on limited proteolysis of cell lysates that profiles drug-associated changes in regional protein accessibility at peptide-level resolution. Here, we applied CoPPRA to ruxolitinib and ulixertinib, individually and in combination, in AML-related cell lysates. Our findings extend conjunctive targeting (CT), a recently proposed mechanism of combinatorial drug action in which combined exposure produces protein targeting patterns not observed with either drug alone. Previously identified through combination-associated changes in protein solubility/stability, CT is examined here at peptide-level resolution through regional differences in proteolytic accessibility. The ruxolitinib-ulixertinib combination produced broad peptide-level accessibility changes, including a subset meeting the predefined criteria for CT. CT candidates predominantly exhibited regional accessibility changes, with altered peptide regions occurring against comparatively small changes across the remaining quantified peptides from the same proteins. MAP2K1 and ATP6V1G1 showed pronounced differences between overlapping peptide sequences, highlighting localized variation in combination-associated accessibility, including an ATP6V1G1 peptide mapping to an annotated helical region. Combination-associated increases in peptide signals were also observed in PIK3R1, BRD4, and PTPN11, linking regional accessibility changes to signaling and transcriptional regulators relevant to AML. Functional enrichment and network analyses further implicated nucleotide and glucose metabolism, ficolin-1-rich granules, ribosome-associated processes, and phagocytic vesicles. These results extend conjunctive targeting from protein-level solubility/stability changes to regional differences in proteolytic accessibility, showing that combination-associated effects can be concentrated within specific peptide regions rather than distributed uniformly across proteins. More broadly, CoPPRA provides a peptide-resolved approach for investigating the molecular features of combinatorial drug action and prioritizing protein regions for subsequent mechanistic validation.

biochemistry↗
bioRxiv2026

Structural and biochemical characterisation of an iterative GCN5-related N-acetyltransferase required for fungal siderophore tailoring

Siderophore-mediated iron acquisition is essential for fungal survival, particularly under iron-limiting conditions. In Aspergillus fumigatus, SidG, a member of the GCN5-related N-acetyltransferase (GNAT) superfamily, catalyses the final step in the biosynthesis of the extracellular siderophore triacetylfusarinine C (TAFC) through sequential acetylation of the precursor fusarinine C (FsC). However, the timing, catalytic mechanism, and functional significance of this modification are not fully understood. Here, we reconstituted SidG activity in vitro and combined native mass spectrometry, X-ray crystallography, molecular dynamics simulations, and site-directed mutagenesis to investigate its catalytic properties. Our analyses demonstrate that SidG selectively binds acetyl-CoA from the cellular milieu and iteratively acetylates the FsC scaffold prior to iron chelation. Structural, biochemical, and molecular dynamics analyses support a direct transfer mechanism, identify key catalytic residues, and demonstrate the strict selectivity of SidG for short-chain acyl-CoA donors. Together, these findings establish the molecular basis for SidG-dependent siderophore tailoring and expand our understanding of GNAT-catalysed transformations in fungal natural product biosynthesis.

biochemistry↗