Search bioRxiv⌕ Search
Home/Archive/bioRxiv

bioRxiv · 10.1101/2025.06.12.658902

The soluble HIV-1 Vpu protein interacts with calmodulin in a Ca2+-dependent manner

Ishola, O.·Islam, M. M.·Hadadianpour, E.·Borbat, P. P.·Georgieva, E. R.
View original source ↗Export metadata ↓

Abstract

The HIV-1 Vpu membrane protein is crucial to the virus lifecycle. Our recent studies revealed soluble Vpu oligomers, prompting further investigation into their interactions with cellular proteins. Notably, Vpu may form a complex with calmodulin (CaM) due to its putative CaM-binding motif; however, experimental proof of this association remained unavailable. Here, we present definitive experimental evidence that the soluble Vpu complex interacts in vitro with calcium-bound CaM (Ca2+-CaM) its active form. Using double electron electron-resonance (DEER) spectroscopy and protein spin labeling, we detected the formation of a soluble Vpu-Ca2+-CaM complex. Both the full-length (FL) and truncated C-terminal regions of Vpu bind Ca2+-CaM. DEER experiments on a spin-labeled CaM cysteine mutant S39C/A103C revealed that, upon association with Vpu, Ca2+-CaM undergoes a transition from an open to a more closed conformation, consistent with previous reports of Ca2+-CaM interactions with other proteins. Furthermore, we observed that the binding of Vpu to Ca2+-CaM leads to dissociation of soluble Vpu oligomers, as evidenced by a reduction in DEER modulation depth for FL Vpu spin-labeled at residue L42C. FRET analysis with a fluorescently labeled C-terminal cysteine mutant of Vpu confirmed this result. Like FL Vpu, the Vpu C-terminal region forms soluble homooligomers that dissociate upon binding to Ca2+-CaM. Collectively, our results suggest that soluble Vpu and Ca2+-CaM form an equimolar complex. DEER analysis of Vpu C-terminal region spin-labeled at residues Q36C/I61C demonstrated that Vpu undergoes significant conformational changes to facilitate Ca2+-CaM binding. These findings could be relevant to Vpu-CaM interactions under physiological conditions.

Source connections

Explore related subjects

biophysicsPreprint

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Ishola, O., Islam, M. M., Hadadianpour, E., Borbat, P. P., Georgieva, E. R.. 2025-06-17. The soluble HIV-1 Vpu protein interacts with calmodulin in a Ca2+-dependent manner. https://doi.org/10.1101/2025.06.12.658902

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

KEEP EXPLORING

Related preprints

bioRxiv2026

Design of colipids with controlled lateral distance of head group moieties for targeting strategies in the field of lipid-based nanoparticles

Lipid nanoparticles and liposomes are nanoparticle drug formulations which are firmly established in clinics. In order to expand their application and improve efficacy, surface modifications can be a key strategy, especially for cell specific targeting. Targeting can be achieved by integrating ligand functionalized lipids or lipidoids on the nanoparticle surface. In this case, not solely the targeting ligand itself, but also the structure of the whole targeting lipid/lipidoid can affect the interaction of the targeting ligand with the binding motive on cells. Especially, distal spacer structures between lipid anchor and ligand unit, often composed of polyethylene glycol chains, provide a certain distance of the ligand from the nanoparticle surface. A concept which is currently neglected is the control of the lateral distance between ligand structures on the nanoparticle. Herein we investigated the possibility to design lipidoids with a lateral spacer composed of polyethylene glycol units. We synthesized and characterized different lipidoids which provide a primary amine in the head group for possible ligand coupling. In our model lipidoids the head groups were functionalized with a paramagnetic probe to apply electron paramagnetic resonance (EPR) methods for the characterization of the lipidoid interaction with model nanoparticles, in our case liposomes. Continuous wave EPR was used to study the efficiency of the novel lipidoids to integrate into lipid bilayers of model liposomes, which was shown to depend on lipidoid structure and liposome composition. Furthermore, using double electron-electron resonance (DEER), we observed lipidoid conformational changes occurring upon integration into liposomes.

biophysics↗
bioRxiv2026

Binding mechanisms of therapeutic antibodies to human claudin-18.2

Claudin-18.2 (CLDN18.2) is a tight junction component with highly restricted expression in the paracellular space of nonmalignant gastric epithelial cells. It becomes accessible on tumor cell surface during malignant transformation, making CLDN18.2 an attractive target for targeted therapies against gastric cancer. Recently, zolbetuximab has become the first FDA-approved monoclonal antibody that targets CLDN18.2 in advanced gastric cancer, and others like osemitamab have entered phase 3 clinical trials. However, the high-resolution structure of CLDN18.2 is lacking, and how CLDN18.2 is recognized by therapeutic antibodies remains undefined. Here, we report cryo-EM structures of human claudin-18.2 (hCLDN18.2) in complex with the Fab fragments of zolbetuximab and osemitamab, revealing the structure of hCLDN18.2 and its binding mechanism to the therapeutic antibodies. Further analyses reveal that three residues in the first extracellular loop of hCLDN18.2 that are different from human claudin-18.1 (hCLDN18.1) play a critical role in antibody binding. Our data elucidate the structural basis for selective binding of therapeutic antibodies to hCLDN18.2, which should aid rational design of next-generation immunotherapies targeting hCLDN18.2.

biophysics↗
bioRxiv2026

Structural relationships between the SLC12 cotransporter C-terminal domain, universal stress proteins and adenylating enzymes

Several SLC12 cotransporters bind ATP in a cytoplasmic C-terminal domain (CTD). We analysed 16,192 CTD-containing SLC12 sequences and compared 42,845 representative structures to examine the relationship between this nucleotide site, universal stress proteins (USPs) and adenylating enzymes. In phosphorylated NKCC1, D891 and D927 lie near the ATP phosphate chain, while R801 and K889 form a basic phosphate-binding clamp. NKCC1 retains this arrangement, whereas KCC paralogs replace or lose several corresponding groups. In structural comparisons with USP and adenylating-enzyme references, both CTD lobes score between universal stress proteins and EC-annotated domains, and the two lobes form separate lineages that include bacterial transporters. Lobe-specific and nucleotide-frame comparisons place ATP in the corresponding structural region used for -phosphate chemistry by catalytic members of this fold. Published work on UspG provides a precedent for protein-bound AMP in a natural USP. In the examined SLC12 structures and USP models, candidate protein hydroxyls lack an in-line geometry for attack at ATP P. Protein adenylation would require a change in protein or nucleotide geometry, or a different acceptor. These results define a structural basis for testing conditional protein adenylation at SLC12 nucleotide sites. The required evidence is a covalent protein-AMP adduct, identification of its acceptor and measurement of the expected pyrophosphate coproduct, with soluble nucleotide analysis to distinguish accompanying ATP reactions.

biophysics↗