The placenta acts as physical and immunological barrier against the transmission of viruses and bacteria from mother to fetus. However, the specific mechanisms by which the placenta protects the developing fetus from viral and bacterial pathogens are poorly understood. To identify placental peptides and small proteins protecting from viral and bacterial infections, we generated a peptide library from 10 kg placenta by chromatographic means. Screening the resulting 250 fractions against Herpes-Simplex-Virus 2 (HSV-2), which is rarely transmitted through the placenta, in a cell-based system identified two adjacent fractions with significant antiviral activity. Further rounds of chromatographic purification and anti-HSV-2 testing allowed to purify the bioactive peptide. Mass spectrometry revealed the presence of a 36-mer derived from the C-terminal region of the hemoglobin β subunit. The purified and corresponding chemically synthesized peptide, termed HBB(112-147), inhibited HSV-2 infection in a dose-dependent manner, with a mean IC50 in the median μg/ml range. Full-length hemoglobin tetramer had no antiviral activity. HBB(112-147) did not impair infectivity by direct targeting of the virions but prevented HSV-2 infection at the cell entry level. The peptide was inactive against Human Immunodeficiency Virus Type 1, Rubella and Zika virus infection, suggesting a specific anti-HSV-2 mechanism. Notably, HBB(112-147) has previously been identified as broad-spectrum antibacterial agent. It is abundant in placenta, reaching concentrations between 280 and 740 μg/ml, that are well sufficient to inhibit HSV-2 and prototype Gram-positive and -negative bacteria. We here additionally show, that HBB(112-147) also acts potently against Pseudomonas aeruginosa strains (including a multi-drug resistant strain) in a dose dependent manner, while full-length hemoglobin is inactive. Interestingly, the antibacterial activity of HBB(112-147) was increased under acidic conditions, a hallmark of infection and inflammatory conditions. Indeed, we found that HBB(112-147) is released from the hemoglobin precursor by Cathepsin D and Napsin A, acidic proteases highly expressed in placental and other tissues. We propose that upon viral or bacterial infection, the abundant hemoglobin precursor is proteolytically processed to release HBB(112-147), a broadly active antimicrobial innate immune defense peptide.

中文翻译：

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胎盘衍生的β-血红蛋白C末端片段，具有抗菌和抗病毒活性。

胎盘充当病毒和细菌从母亲到胎儿的传播的物理和免疫屏障。但是，人们对胎盘保护发育中的胎儿免受病毒和细菌病原体侵害的具体机制了解甚少。为鉴定胎盘肽和保护免受病毒和细菌感染的小蛋白，我们通过色谱方法从10千克胎盘中生成了一个肽库。在基于细胞的系统中，筛选出很少通过胎盘传播的抗单纯疱疹病毒2（HSV-2）的250个馏分，鉴定出两个相邻的具有显着抗病毒活性的馏分。进一步的色谱纯化和抗HSV-2试验可以纯化生物活性肽。质谱显示存在来自血红蛋白β亚基的C末端区域的36聚体的存在。纯化后的相应化学合成肽（称为HBB（112-147））以剂量依赖性方式抑制HSV-2感染，平均IC50处于中位μg/ ml范围内。全长血红蛋白四聚体没有抗病毒活性。HBB（112-147）不会通过直接靶向病毒粒子来削弱感染性，但可在细胞进入水平上预防HSV-2感染。该肽对人免疫缺陷病毒1型，风疹和寨卡病毒感染无活性，表明有特定的抗HSV-2机制。值得注意的是，HBB（112-147）先前已被确定为广谱抗菌剂。它在胎盘中含量很高，浓度在280至740μg/ ml之间，足以抑制HSV-2和原型革兰氏阳性和阴性细菌。我们在这里还显示，HBB（112-147）还以剂量依赖的方式有效地对抗铜绿假单胞菌菌株（包括多药耐药菌株），而全长血红蛋白则没有活性。有趣的是，HBB（112-147）的抗菌活性在酸性条件下增加，而酸性条件是感染和炎症条件的标志。确实，我们发现组织蛋白酶D和Napsin A是在胎盘和其他组织中高度表达的酸性蛋白酶，从血红蛋白前体中释放出HBB（112-147）。我们建议，在病毒或细菌感染后，大量的血红蛋白前体经过蛋白水解处理以释放HBB（112-147），这是一种具有广泛活性的抗微生物先天免疫防御肽。