Iron enhances the binding rates and translational efficiency of iron responsive elements (IREs) mRNA with initiation factor eIF4F

Effects of Maternal Dietary Enteromorpha prolifera Polysaccharide Iron Supplement on Mineral Elements and Iron Level of Neonatal Piglets

Iron plays a key role in maternal health during pregnancy and fetal growth. Enteromorpha polysaccharide-iron (EP-Fe) as an organic iron chelate may improve the iron transmission of mother and offspring, ameliorate the poor pregnancy outcomes of sows, and alleviate the growth restriction of piglets caused by iron deficiency. This study aimed to evaluate the effects of maternal dietary supplementation with EP-Fe on reproductive performance and placental iron transmission of sows, as well as growth performance of piglets. Sixty pregnant sows at the 95th day of gestation were randomly divided into control group and EP-Fe group (EP-Fe, 139 mg kg-1). Blood samples of sows and neonatal piglets, colostrum, and tissue samples were collected on the day of delivery. The animal experiment ended at the 21st day of post-delivery. Results showed that maternal dietary EP-Fe increased colostrum iron (P < 0.05) of sows, as well as final litter weight (P < 0.05) and average daily weight of piglets (P < 0.05) during days 1-21 of lactation, as well as iron and manganese content in umbilical cord blood (P < 0.05) and hepatic iron of neonatal piglets (P < 0.01), and decreased fecal iron (P < 0.001), serum calcium (P < 0.05), phosphorus (P < 0.05), and zinc (P < 0.01) in the parturient sow. RT-qPCR results showed that Fpn1 and Zip14 in placenta, as well as TfR1 and Zip14 in duodenum of neonatal piglets, were activated by maternal EP-Fe supplement. These findings suggest that maternal dietary EP-Fe could increase iron storage of neonatal piglets via improving placental iron transport and iron secretion in colostrum, thus enhancing the growth performance of sucking piglets.

Poly(A)-binding protein promotes VPg-dependent translation of potyvirus through enhanced binding of phosphorylated eIFiso4F and eIFiso4F∙eIF4B

The phosphorylation of eukaryotic translational initiation factors has been shown to play a significant role in controlling the synthesis of protein. Viral infection, environmental stress, and growth circumstances cause phosphorylation or dephosphorylation of plant initiation factors. Our findings indicate that casein kinase 2 can phosphorylate recombinant wheat eIFiso4E and eIFiso4G generated from E. coli in vitro. For wheat eIFiso4E, Ser-207 was found to be the in vitro phosphorylation site. eIFiso4E lacks an amino acid that can be phosphorylated at the position corresponding to Ser-209, the phosphorylation site in mammalian eIF4E, yet phosphorylation of eIFiso4E has effects on VPg binding affinity that are similar to those of phosphorylation of mammalian eIF4E. The addition of VPg and phosphorylated eIFiso4F to depleted wheat germ extract (WGE) leads to enhancement of translation of both uncapped and capped viral mRNA. The addition of PABP together with eIFiso4Fp and eIF4B to depleted WGE increases both uncapped and capped mRNA translation. However, it exhibits a translational advantage specifically for uncapped mRNA, implying that the phosphorylation of eIFiso4F hinders cap binding while promoting VPg binding, thereby facilitating uncapped translation. These findings indicate TEV virus mediates VPg-dependent translation by engaging a mechanism entailing phosphorylated eIFiso4Fp and PABP. To elucidate the molecular mechanisms underlying these observed effects, we studied the impact of PABP and/or eIF4B on the binding of VPg with eIFiso4Fp. The inclusion of PABP and eIF4B with eIFiso4Fp resulted in about 2-fold increase in affinity for VPg (Kd = 24 ± 1.7 nM), as compared to the affinity of eIFiso4Fp alone (Kd = 41.0 ± 3.1 nM). The interactions between VPg and eIFiso4Fp were determined to be both enthalpically and entropically favorable, with the enthalpic contribution accounting for 76-97% of the ΔG at 25°C, indicating a substantial role of hydrogen bonding in enhancing the stability of the complex. The binding of PABP to eIFiso4Fp·4B resulted in a conformational alteration, leading to a significant enhancement in the binding affinity to VPg. These observations suggest PABP enhances the affinity between eIFiso4Fp and VPg, leading to an overall conformational change that provides a stable platform for efficient viral translation.

Iron response elements (IREs)-mRNA of Alzheimer's amyloid precursor protein binding to iron regulatory protein (IRP1): a combined molecular docking and spectroscopic approach

The interaction between the stem-loop structure of the Alzheimer's amyloid precursor protein IRE mRNA and iron regulatory protein was examined by employing molecular docking and multi-spectroscopic techniques. A detailed molecular docking analysis of APP IRE mRNA∙IRP1 reveals that 11 residues are involved in hydrogen bonding as the main driving force for the interaction. Fluorescence binding results revealed a strong interaction between APP IRE mRNA and IRP1 with a binding affinity and an average binding sites of 31.3 × 10⁶ M^-1 and 1.0, respectively. Addition of Fe²⁺(anaerobic) showed a decreased (3.3-fold) binding affinity of APP mRNA∙IRP1. Further, thermodynamic parameters of APP mRNA∙IRP1 interactions were an enthalpy-driven and entropy-favored event, with a large negative ΔH (-25.7 ± 2.5 kJ/mol) and a positive ΔS (65.0 ± 3.7 J/mol·K). A negative ΔH value for the complex formation suggested the contribution of hydrogen bonds and van der Waals forces. The addition of iron increased the enthalpic contribution by 38% and decreased the entropic influence by 97%. Furthermore, the stopped-flow kinetics of APP IRE mRNA∙IRP1 also confirmed the complex formation, having the rate of association (k_on) and the rate of dissociation (k_off) as 341 μM^-1 s^-1, and 11 s^-1, respectively. The addition of Fe²⁺ has decreased the rate of association (k_on) by ~ three-fold, whereas the rate of dissociation (k_off) has increased by ~ two-fold. The activation energy for APP mRNA∙IRP1 complex was 52.5 ± 2.1 kJ/mol. The addition of Fe²⁺ changed appreciably the activation energy for the binding of APP mRNA with IRP1. Moreover, circular dichroism spectroscopy has confirmed further the APP mRNA∙IRP1 complex formation and IRP1 secondary structure change with the addition of APP mRNA. In the interaction between APP mRNA and IRP1, iron promotes structural changes in the APP IRE mRNA∙IRP1 complexes by changing the number of hydrogen bonds and promoting a conformational change in the IRP1 structure when it is bound to the APP IRE mRNA. It further illustrates how IRE stem-loop structure influences selectively the thermodynamics and kinetics of these protein-RNA interactions.

Phosphorylation of eukaryotic initiation factor eIFiso4E enhances the binding rates to VPg of turnip mosaic virus

Binding of phosphorylated eIFiso4E with viral genome-linked protein (VPg) of turnip mosaic virus was examined by stopped-flow, fluorescence, circular dichroism (CD) spectroscopy, and molecular docking analysis. Phosphorylation of eIFiso4E increased (4-fold) the binding rates as compared to unphosphorylated eIFiso4E with VPg. Stopped-flow kinetic studies of phosphorylated eIFiso4E with VPg showed a concentration-independent conformational change. The dissociation rate was about 3-fold slower for eIFiso4E∙VPg complex upon phosphorylation. Phosphorylation enhanced the association rates and lowered the dissociation rates for the eIFiso4E∙VPg binding, with having higher preferential binding to eIFiso4Ep. Binding rates for the interaction of eIFiso4Ep with VPg increased (6-fold) with an increase in temperature, 278 K to 298 K. The activation energies for binding of eIFiso4Ep and eIFiso4E with VPg were 37.2 ± 2.8 and 52.6 ± 3.6 kJ/mol, respectively. Phosphorylation decreased the activation energy for the binding of eIFiso4E to VPg. The reduced energy barrier suggests more stable platform for eIFiso4Ep∙VPg initiation complex formation, which was further supported by molecular docking analysis. Moreover, far-UV CD studies revealed that VPg formed complex with eIFiso4Ep with substantial change in the secondary structure. These results suggested that phosphorylation, not only reduced the energy barrier and dissociation rate but also enhanced binding rate, and an overall conformational change, which provides a more stable platform for efficient viral translation.

Hereditary Hyperferritinemia Cataract Syndrome: Ferritin L Gene and Physiopathology behind the Disease-Report of New Cases

Hereditary hyperferritinemia-cataract syndrome (HHCS) is a rare disease characterized by high serum ferritin levels, congenital bilateral cataracts, and the absence of tissue iron overload. This disorder is produced by mutations in the iron responsive element (IRE) located in the 5' untranslated regions (UTR) of the light ferritin (FTL) gene. A canonical IRE is a mRNA structure that interacts with the iron regulatory proteins (IRP1 and IRP2) to post-transcriptionally regulate the expression of proteins related to iron metabolism. Ferritin L and H are the proteins responsible for iron storage and intracellular distribution. Mutations in the FTL IRE abrogate the interaction of FTL mRNA with the IRPs, and de-repress the expression of FTL protein. Subsequently, there is an overproduction of ferritin that accumulates in serum (hyperferritinemia) and excess ferritin precipitates in the lens, producing cataracts. To illustrate this disease, we report two new families affected with hereditary hyperferritinemia-cataract syndrome with previous known mutations. In the diagnosis of congenital bilateral cataracts, HHCS should be taken into consideration and, therefore, it is important to test serum ferritin levels in patients with cataracts.