The Physiological Role of Ferritin-Like Compounds in Bacteria

Iron, as the ferrous or ferric ion, is essential for the life processes of all eukaryotes and most prokaryotes; however, the element is toxic when in excess of that needed for cellular homeostasis. Ferrous ions can react with metabolically generated hydrogen peroxide to yield toxic hydroxyl radicals that in turn degrade lipids, DNA, and other cellular biomolecules. Mechanisms have evolved in living systems for iron detoxification and for the removal of excess ferrous ions from the cytosol. These detoxification mechanisms involve the oxidation of excess ferrous ions to the ferric state and storage of the ferric ions in ferritin-like proteins.

There are at least three types of ferritin-like proteins in bacteria: bacterial ferritin, bacterioferritin, and dodecameric ferritin. These bacterial proteins are related to the ferritins found in eukaryotes. The structure and physical characteristics of the ferritin-like compounds have been elucidated in several bacteria. Unfortunately, the physiological roles of the bacterial ferritin-like compounds have been less thoroughly studied. A few studies conducted with mutants indicated that ferritin-like compounds can protect bacterial cells from iron overload, serve as an iron source when iron is limited, protect the bacterial cells against oxidative stress and/or protect DNA against enzymatic or oxidative attack. There is very little information available concerning the roles that ferritin-like compounds might play in the survival of bacteria in food, water, soil, or eukaryotic host environments.     

Quantifying and visualizing weak interactions between anions and proteins

The molecular properties of proteins are influenced by various ions present in the same solution. While site-specific strong interactions between multivalent metal ions and proteins are well characterized, the behavior of other ions that are only weakly interacting with proteins remains elusive. In the current study, using NMR spectroscopy, we have investigated anion–protein interactions for three proteins that are similar in size but differ in overall charge. Using a unique NMR-based approach, we quantified anions accumulated around the proteins. The determined numbers of anions that are electrostatically attracted to the charged proteins were notably smaller than the overall charge valences and were consistent with predictions from the Poisson–Boltzmann theory. This NMR-based approach also allowed us to measure ionic diffusion and characterize the anions interacting with the positively charged proteins. Our data show that these anions rapidly diffuse while bound to the proteins. Using the same experimental approach, we observed the release of the anions from the protein surface upon the formation of the Antp homeodomain–DNA complex. Using paramagnetic relaxation enhancement (PRE), we visualized the spatial distribution of anions around the free proteins and the Antp homeodomain–DNA complex. The obtained PRE data revealed the localization of anions in the vicinity of the highly positively charged regions of the free Antp homeodomain and provided further evidence of the release of anions from the protein surface upon the protein–DNA association. This study sheds light on the dynamic behavior of anions that electrostatically interact with proteins.

Biological systems involve various inorganic and organic ions. Protein functions are influenced by the surrounding ions not only through the electrostatic screening effect (1), but also through direct interactions at the molecular surfaces (2). Compared to typical protein–ligand interactions, protein–ion interactions are weaker and more transient, yet ions can significantly influence various properties such as solubility, stability, and functional activities of proteins (3). The influences depend on ionic species. For example, when Cl⁻ ions are replaced with glutamate ions in biochemical experiments, some DNA-binding proteins exhibit substantially stronger (>100-fold for some cases) affinity for DNA (4, 5). To understand how ions affect the molecular properties of proteins, the behavior of ions around proteins should be elucidated.For DNA and RNA, ion-counting methods have greatly advanced experiment-based knowledge of ionic interactions (6, 7). These methods were successfully used to examine and validate theoretical models for ion–nucleic acid interactions (8, 9). However, ion-counting methods do not provide any information about the spatial distribution and dynamic properties of counterions around macromolecules. Even at high resolution in crystal structures, the vast majority of counterions are unresolved, suggesting that they are highly mobile. The dynamic nature of ions causes a major difficulty in studying the interactions between ions and biological macromolecules.Weak transient interactions of monovalent ions with proteins are particularly difficult to capture by experiments. Unlike nucleic acids that possess a negative charge at every residue, proteins typically contain both positively charged and negatively charged residues as well as many neutral residues. Consequently, proteins possess a far smaller overall charge than nucleic acids of similar molecular size. This implies that the electrostatic attraction of ions to proteins could be intrinsically weaker than that to nucleic acids. Furthermore, local environments around individual charged moieties of proteins are more diverse compared to those of nucleic acids. Although NMR spectroscopy is powerful for investigating various physicochemical properties of proteins (10, 11), there has been a lack of methods suited to quantitatively investigate ion–protein interactions. Experimental studies of weak ion–protein interactions have been challenging (3).In this work, using unique experimental methods, we study how anions behave in the vicinity of proteins. Our NMR-based approach allows us to determine how many anions are attracted to proteins. Our data show that the number is significantly smaller than the overall charge valence of each positively charged protein. We explain this observation using the concept of the ion atmosphere and theoretical calculations based on the Poisson–Boltzmann equation. Our experimental approach also reveals the diffusional properties of anions interacting with proteins and unravels the release of anions from the protein surface upon protein–DNA association. Furthermore, our solvent paramagnetic relaxation enhancement (PRE) data show how anions are spatially distributed around the protein surface and how their distribution changes when the protein binds to DNA. Our study sheds light on the dynamic behavior of counterions around proteins.     

磁敏感加权成像脑铁含量感兴趣区选择及测量研究

目的探讨苍白球区异常矿物质沉积时,选取不同感兴趣区(region of interest,ROI)(整个苍白球或局部矿物质沉积区域)对铁含量测值的影响,从而为脑组织铁含量测定感兴趣区选择及其测量的便捷性提供依据。材料与方法采用常规磁共振成像和磁敏感加权成像扫描94例健康志愿者,其中苍白球区存在明显矿物质沉积10例,分别选取苍白球整体(A1组)及局部矿物质沉积区域(A2组)为ROI测量灰度值。另外选取性别和年龄相匹配的苍白球区无异常铁含量沉积10例作为对照组(B组)。通过Pearson线性相关分析比较苍白球区有无异常铁含量沉积时的信号值对苍白球区铁含量测量的影响。结果 A1组和A2组灰度值测量相关系数r=0.827(P0.05),整个苍白球区灰度值测量与局部区域灰度值测量具有显著一致性;A1组和B组相关系数r=0.183(P0.05),A2组和B组间相关系数r=0.344(P0.05),说明苍白球区内有无矿物质沉积对灰度值测量影响具有统计学意义。结论通过SWI技术分析含有异常矿物质沉积的苍白球区,选取整个苍白球区作为ROI与只将异常的矿物质沉积区作为ROI反映矿物质沉积趋势具有一致性,对脑铁测量影响不大,因此可以直接选取苍白球整体区域作为ROI测量脑铁含量,方法便捷,值得临床推广应用。     

3.0T MRI IdealIQ序列评价成人肝铁浓度与脂肪分数的相关性

目的 检测中国汉族健康人群的肝脏脂肪分数及肝储铁水平,并评价脂肪分数及肝储铁水平相关性。方法 应用GE Discovery MR750W测定45名受检者的肝脏脂肪分数和R2^*值。采用IdealIQ序列进行上腹部扫描,应用AW VolumeShare 5工作站软件,通过在肝脏上选择ROI的方法直接获得R2^*值及肝脂肪分数。采用t检验的方法分别检验不同性别、年龄组间脂肪分数、R2^*值均数的差异,应用Spearman分析的方法分析R2^*值及脂肪分数的相关性。结果 45名健康人肝脏脂肪分数为1.15%~10.26%,R2^*值为46.45~89.30 Hz。男性与女性、青年人与中年人的肝脏FF、R2^*值差异均无统计学意义(P均> 0.05)。脂肪分数与R2^*值呈线性正相关(r=0.432,P=0.003)。结论 运用3.0T MRI IdealIQ序列能够同时测定肝脏脂肪含量及铁浓度,肝脏脂肪含量与肝铁浓度具有显著的相关性。     

缺铁性贫血诊断的研究进展

缺铁性贫血(IDA)是体内贮存铁缺乏,影响血红素合成引起的贫血。IDA为最常见的贫血,目前临床上主要以外周血常规参数、铁代谢参数作为诊断指标,但以上指标敏感性差,易受其他因素的影响,给IDA的诊断带来一定困难。目前,IDA的诊断在某些领域取得了新的研究进展,如通过对铁调素、网织红细胞血红蛋白含量、低血红蛋白浓度的检测,给IDA带来了具有敏感性高、方便、有效的诊断方法,值得临床医师注意。     

Outcome of gastric antral vascular ectasia and related anemia after orthotopic liver transplantation

BACKGROUNDGastric antral vascular ectasia (GAVE) is a significant complication of cirrhosis. Numerous medical, surgical, and endoscopic treatment modalities have been proposed with varied satisfactory results. In a few small studies, GAVE and associated anemia have resolved after orthotopic liver transplantation (OLT). AIMTo assess the impact of OLT on the resolution of GAVE and related anemia.METHODSWe retrospectively reviewed clinical records of adult patients with GAVE who underwent OLT between September 2012 and September 2019. Demographics and other relevant clinical findings were collected, including hemoglobin levels and upper endoscopy findings before and after OLT. The primary outcome was the resolution of GAVE and its related anemia after OLT.RESULTSSixteen patients were identified. Mean pre-OLT Hgb was 7.7 g/dL and mean 12 mo post-OLT Hgb was 11.9 g/dL, (P = 0.001). Anemia improved (defined as Hgb increased by 2g) in 87.5% of patients within 6 to 12 mo after OLT and resolved completely in half of the patients. Post-OLT esophagogastroduodenoscopy was performed in 10 patients, and GAVE was found to have resolved entirely in 6 of those patients (60%). CONCLUSIONAlthough GAVE and associated anemia completely resolved in the majority of our patients after OLT, GAVE persisted in a few patients after transplant. Further studies in a large group of patients are necessary to understand the causality of disease and to better understand the factors associated with the persistence of GAVE post-transplant.     

Efficacy of Essential Trace Elements Supplementation on Mineral Composition,Sperm Characteristics,Antioxidant Status,and Genotoxicity in Testis of Tebuconazole-treated Rats

ObjectiveThis research was performed to evaluate the effect of tebuconazole (TBZ) on reproductive organs of male rats and to assess the protective role of combined essential trace elements in alleviating the detrimental effect of TBZ on male reproductive function.MethodsFor this purpose, 48 rats were exposed to 100 mg/kg TBZ, TBZ supplemented with zinc (Zn), selenium (Se), copper (Cu), and iron (Fe), TBZ + (Se + Zn); TBZ + Cu; or TBZ + Fe. The experiment was conducted for 30 consecutive days.ResultsTBZ caused a significant perturbation in mineral levels and reduction in reproductive organs weights, plasma testosterone level, and testicular antioxidant enzyme activities. The TBZ-treated group also showed a significant increase in sperm abnormalities (count, motility, and viability percent), plasma follicle-stimulating hormone and luteinizing hormone concentrations, lipid peroxidation, protein oxidation, and severe DNA degradation in comparison with the controls. Histopathologically, TBZ caused testis impairments. Conversely, treatment with trace elements, in combination or alone, improved the reproductive organ weights, sperm characteristics, TBZ-induced toxicity, and histopathological modifications in testis.ConclusionTBZ exerts significant harmful effects on male reproductive system. The concurrent administration of trace elements reduces testis dysfunction, fertility, and toxicity induced by TBZ.