Biology subjects

Issaian, A.

Publications and source records attributed to Issaian, A..

5 recordsLinked to original sources

bioRxiv2025

U1 snRNP and RNA polymerase II interaction is predominantly mediated by Prp40 rather than U1-70K in yeast

Transcription and splicing are coupled both temporally and physically. A previous cryo-EM structure of the human U1 snRNP and RNA polymerase pol II complex has shown that U1 snRNP uses predominantly the RRM domain of U1-70K to directly interact with the RPB2 subunit of pol II. However, residues on U1-70K involved in the interaction with pol II are not conserved in yeast U1-70K, raising the question whether yeast U1 snRNP interacts with pol II in a similar manner. We found that yeast pol II associates with both U1 and U2 snRNPs, but U1-70K makes a minimal contribution to U1 snRNPs interaction with pol II. On the other hand, multiple domains of yeast Prp40 interact with pol II and the removal of the C-terminal domain (CTD) of pol II does not affect this interaction. Although yeast Prp40 is stably associated with U1 snRNP, its human homologs, PRPF40a and PRPF40b, are alternative splicing factors that are not integral components of U1 snRNP. This shift of function of Prp40 homologs may have led to the evolution of U1-70K to be the main interactor with pol II in the human system.

biochemistry↗

bioRxiv2025

Caffeine Impairs Red Blood Cell Storage Quality by Dual Inhibition of ADORA2b Signaling and G6PD Activity

Caffeine is the most widely consumed psychoactive substance globally, yet its peripheral physiological effects remain incompletely understood. Leveraging comprehensive data from 13,091 blood donors in the REDS RBC-Omics study, we identify caffeine as a significant modulator of red blood cell (RBC) storage quality and transfusion outcomes. Elevated caffeine levels were reproducible across multiple donations from 643 recalled donors, selected based on their extremes in hemolytic propensity. Both in the screening and recalled cohorts, higher caffeine levels were associated with disrupted RBC metabolism, characterized by reduced glycolysis, depletion of adenylate pools or 2,3-bisphosphoglycerate, and increased markers of oxidative stress and osmotic fragility, including kynurenine accumulation. These observations were recapitulated in plasma and RBCs of eight volunteers upon consumption of a cup of coffee independently of brewing method (Chemex vs espresso). Clinically, elevated caffeine correlated with increased hemolysis and lower post-transfusion hemoglobin increments, especially pronounced in recipients transfused with RBCs from donors carrying common polymorphisms in the ADORA2b gene, a key regulator of RBC metabolism in hypoxia. These human findings were mechanistically validated using a murine model deficient in ADORA2b, which demonstrated impaired glycolytic flux, compromised antioxidant defenses - including caffeine-dependent direct inhibition of recombinantly-expressed glucose 6-phosphate dehydrogenase, and decreased transfusion efficacy (lower hemoglobin increments, higher bilirubin post-transfusion), effects further exacerbated by caffeine exposure during storage. Our study positions caffeine consumption as a modifiable factor in blood transfusion practice, advocating for precision strategies that integrate genetic and exposome factors, and identifies metabolic interventions to enhance blood quality and clinical outcomes. One sentence summaryCaffeine consumption and genetic variants in the ADORA2b receptor synergistically impair red blood cell metabolism and transfusion efficacy, revealing a modifiable exposome-gene interaction for precision transfusion medicine.

biochemistry↗

bioRxiv2022

Small molecule inhibition of multiple RNA binding proteins underlies Musashi-2 independent phenotypes

RNA binding proteins (RBPs) are key regulators of gene expression. Small molecules targeting these RBP-RNA interactions are a rapidly emerging class of therapeutics for treating a variety of diseases. Ro-08-2750 (Ro) is a small molecule inhibitor identified as a competitive inhibitor of Musashi(MSI)-RNA interactions. Here we show Ro potently inhibits adrenocortical steroidogenesis and viability independent of MSI2 in multiple cell lines. We identified Ro-interacting proteins using an unbiased proteome-wide approach and discovered it is broadly targeting RBPs. To confirm this finding, we leveraged the large-scale ENCODE data and found a subset of RBPs whose depletion phenocopies Ro inhibition. We conclude that Ro is a promiscuous inhibitor of multiple RBPs, many containing RRM1 domains. Moreover, we provide a general framework for validating the specificity and identifying targets of RBP inhibitors in a cellular context.

molecular biology↗

bioRxiv2021

Proteolytic Activation of Human-specific Olduvai Domains by the Furin Protease

Olduvai protein domains (formerly DUF1220) show the greatest human-specific increase in copy number of any coding region in the genome and are highly correlated with human brain evolution and cognitive disease. The majority of human copies are found within four NBPF genes organized in a variable number of a tandemly arranged three-domain blocks called Olduvai triplets. Here we show that these human-specific Olduvai domains are posttranslationally processed by the furin protease, with a cleavage site occurring once at each triplet. These findings suggest that all expanded human-specific NBPF genes encode proproteins consisting of many independent Olduvai triplet proteins which are activated by furin processing. The exceptional correlation of Olduvai copy number and brain size taken together with our new furin data, indicates the ultimate target of selection was a rapid increase in dosage of autonomously functioning Olduvai triplet proteins, and that these proteins are the primary active agent underlying Olduvais role in human brain expansion.

evolutionary biology↗

bioRxiv2020

The interactome of the N-terminus of band 3 regulates red blood cell metabolism and storage quality

Band 3 (anion exchanger 1 - AE1) is the most abundant membrane protein in red blood cells (RBCs), the most abundant cell in the human body. A compelling model, based on indirect evidence, posits that - at high oxygen saturation - the N-term cytosolic domain of AE1 binds to and inhibits glycolytic enzymes, thus diverting metabolic fluxes to the pentose phosphate pathway to generate reducing equivalents. Dysfunction of this mechanism occurs during RBC aging or storage under blood bank conditions, suggesting a role for AE1 in the regulation of blood storage quality and efficacy of transfusion - a life-saving intervention for millions of recipients worldwide. Here we leverage two murine models carrying genetic ablations of AE1 to provide the first direct mechanistic evidence of its role in metabolic regulation and blood storage quality. Observations in mice phenocopied those in a human subject lacking expression of AE11-11 (band 3 Neapolis), while common polymorphisms in the region coding for AE11-56 increased susceptibility to osmotic hemolysis in healthy blood donors. Through thermal proteome profiling and cross-linking proteomics, we provide the first comprehensive analysis of the RBC interactome, with a focus on AE11-56 and validate recombinant AE1 interactions with glyceraldehyde 3-phosphate dehydrogenase (GAPDH). Finally, we show that incubation with a cell-penetrating AE11-56 peptide can rescue the metabolic defect in glutathione recycling and boost post-transfusion recoveries of stored RBCs from healthy human donors and genetically ablated mice, paving the way for the in vivo metabolic manipulation of RBCs facing oxidant stress - a landmark of many diseases. Key pointsO_LIGenetic ablation of N-term of band 3 results in significant metabolic aberrations and poor post-transfusion recoveries in mice and humans; C_LIO_LIStructural studies on the N-term of band 3 reveal a complex interactome with several enzymes, including GAPDH; C_LI

biochemistry↗