Plasmodium falciparum is the most deadly and leading cause of morbidity and mortality in Africa. About 90% of all malaria deaths in the world today occur in Sub-Saharan Africa especially in children aged < 5 years. In 2018, it was reported that there were 228 million malaria cases that resulted in 405,000 deaths from 91 countries. Currently, a fully effective and long-lasting preventive malaria vaccine is still elusive therefore more effort is needed to identify better effective vaccine candidates. The aim of this study was to identify and characterize hypothetical proteins as vaccine candidates derived from Plasmodium falciparum 3D7 genome by reverse vaccinology. Of the 23 selected hypothetical proteins, 5 were predicted on the extracellular localization by WoLFPSORTv.2.0 program and all the 5 had less than 2 transmembrane regions that were predicted by TMHMMv2.0 and HMMTOP programs at default settings. Two out of the five proteins lacked secretory signal peptides as predicted by SignalP program. Among the 5 extracellular proteins, 3 were predicted to be antigenic by VaxiJen (score ≥ 0.5) and had negative GRAVY values ranging from − 1.156 to − 0.440. B cell epitope prediction by ABCpred and BCpred programs revealed a total of 15 antigenic epitopes. A total of 13 cytotoxic T cells were predicted from the 3 proteins using CTLPred online server. Only 2 out of the 13 CTL were antigenic, immunogenic, non-allergenic, and non-toxic using VaxiJen, IEDB, AllergenFp, and Toxinpred servers respectively in that order. Five HTL peptides from XP_001351030.1 protein are predicted inducers of all the three cytokines. STRING protein–protein network analysis of HPs revealed XP_001350955.1 closely interacts with nucleoside diphosphate kinase (PF13-0349) at 0.704, XP_001351030.1 interacts with male development protein1 (Mdv-1) at 0.645, and XP_001351047.1 with an uncharacterized protein (MAL8P1.53) at 0.400. Reverse vaccinology is a promising strategy for the screening and identification of antigenic antigens with potential capacity to elicit cellular and humoral immune responses against P. falciparum infection. In this study, potential vaccine candidates of Plasmodium falciparum were identified and screened using standard bioinformatics tools. The vaccine candidates contained antigenic and immunogenic epitopes which could be considered for novel and effective vaccine targets. However, we strongly recommend in vivo and in vitro experiments to validate their immunogenicity and protective efficacy to completely decipher the vaccine targets against malaria.

中文翻译：

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使用反向疫苗学筛选和表征恶性疟原虫的假设蛋白作为抗击疟疾的新型候选疫苗


恶性疟原虫是非洲发病率和死亡率最致命的主要原因。当今世界约 90% 的疟疾死亡发生在撒哈拉以南非洲地区，尤其是 5 岁以下的儿童。据报道，2018年，91个国家发生了2.28亿例疟疾病例，导致405,000人死亡。目前，完全有效且持久的预防性疟疾疫苗仍然难以实现，因此需要付出更多努力来确定更有效的候选疫苗。本研究的目的是通过反向疫苗学鉴定和表征作为源自恶性疟原虫 3D7 基因组的候选疫苗的假设蛋白质。在 23 个选定的假设蛋白中，有 5 个是由 WoLFPSORTv.2.0 程序预测的细胞外定位，并且所有 5 个蛋白的跨膜区域均少于 2 个，这是由 TMHMMv2.0 和 HMMTOP 程序在默认设置下预测的。正如 SignalP 程序预测的那样，五种蛋白质中有两种缺乏分泌信号肽。在 5 种胞外蛋白中，VaxiJen 预测 3 种具有抗原性（分数 ≥ 0.5），并且 GRAVY 值范围为 − 1.156 至 − 0.440 为负值。 ABCpred 和 BCpred 程序的 B 细胞表位预测总共揭示了 15 个抗原表位。使用 CTLPred 在线服务器从 3 种蛋白质中预测出总共 13 种细胞毒性 T 细胞。分别按 VaxiJen、IEDB、AllergenFp 和 Toxinpred 服务器的顺序，13 个 CTL 中只有 2 个具有抗原性、免疫原性、非过敏性和无毒性。 XP_001351030.1 蛋白中的 5 个 HTL 肽被预测为所有三种细胞因子的诱导物。 HP 的 STRING 蛋白-蛋白网络分析显示 XP_001350955.1 与核苷二磷酸激酶 (PF13-0349) 密切相互作用，相互作用比例为 0.704，XP_001351030。XP_001351047.1 与雄性发育蛋白 1 (Mdv-1) 在 0.645 处相互作用，XP_001351047.1 在 0.400 处与未表征的蛋白 (MAL8P1.53) 相互作用。反向疫苗学是一种有前途的筛选和鉴定抗原的策略，其具有引发针对恶性疟原虫感染的细胞和体液免疫反应的潜在能力。在这项研究中，使用标准生物信息学工具鉴定和筛选了恶性疟原虫的潜在候选疫苗。候选疫苗含有抗原性和免疫原性表位，可考虑作为新型有效的疫苗靶点。然而，我们强烈建议进行体内和体外实验来验证其免疫原性和保护功效，以彻底破译针对疟疾的疫苗靶点。