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Candidatus Liberibacter spp. are insect-vectored, fastidious, and vascular-limited phytopathogens. They are the presumptive causal agents of potato zebra chip, tomato vein clearing, and the devastating citrus greening disease worldwide. There is an urgent need to develop new strategies to control them. In this study, we characterized a dual-specificity serine/tyrosine phosphatase (STP) that is well conserved among thirty-three geographically diverse Candidatus Liberibacter spp. and strains that infect multiple Solanaceaea and citrus spp. The STP is expressed in infected plant tissues, localized at the plant cytosol and plasma membrane, and interferes with plant cell death responses. We employed an in silico target-based molecular modeling and ligand screen to identify two small molecules with high binding affinity to STP. Efficacy studies demonstrated that the two molecules can inhibit Candidatus Liberibacter spp. but not unrelated pathogens and confer plant disease tolerance. The inhibitors and strategies are promising means to control Candidatus Liberibacter spp.

Citrus greening, also known as Huanglongbing (HLB), is caused by the unculturable bacterium Candidatus Liberibacter spp. (e.g., CLas), and has caused a devastating decline in citrus production in many areas of the world. As of yet, there are no definitive treatments for controlling the disease. Antimicrobial peptides (AMPs) that have the potential to block secretion-dependent effector proteins at the outer-membrane domains were screened in silico. Predictions of drug-receptor interactions were built using multiple in silico techniques, including molecular docking analysis, molecular dynamics, molecular mechanics generalized Born surface area analysis, and principal component analysis. The efflux pump TolC of the Type 1 secretion system interacted with natural bacteriocin plantaricin JLA-9, blocking the β barrel. The trajectory-based principal component analysis revealed the possible binding mechanism of the peptides. Furthermore, in vitro assays using two closely related culturable surrogates of CLas (Liberibacter crescens and Rhizobium spp.) showed that Plantaricin JLA-9 and two other screened AMPs inhibited bacterial growth and caused mortality. The findings contribute to designing effective therapies to manage plant diseases associated with Candidatus Liberibacter spp.

Aims Huanglongbing (citrus greening) is a plant disease putatively caused by the unculturable Gram-negative bacterium Candidatus Liberibacter asiaticus (CLas), and it has caused severe damage to citrus plantations worldwide. There are no definitive treatments for this disease, and conventional disease control techniques have shown limited efficacy. This work presents an in silico evaluation of using specifically targeting anti-microbial peptides (STAMPs) consisting of a targeting segment and an antimicrobial segment to inhibit citrus greening by inhibiting the BamA protein of CLas, which is an outer membrane protein crucial for bacterial viability. Methods and results Initially, a set of peptides with a high affinity toward BamA protein were screened and evaluated via molecular docking and molecular dynamics simulations and were verified in vitro via bio-layer interferometry (BLI). In silico studies and BLI experiments indicated that two peptides, HASP2 and HASP3, showed stable binding to BamA. Protein structures for STAMPs were created by fusing known anti-microbial peptides (AMPs) with the selected short peptides. The binding of STAMPs to BamA was assessed using molecular docking and binding energy calculations. The attachment of high-affinity short peptides significantly reduced the free energy of binding for AMPs, suggesting that it would make it easier for the STAMPs to bind to BamA. Efficacy testing in vitro using a closely related CLas surrogate bacterium showed that STAMPs had greater inhibitory activity than AMP alone. Conclusions In silico and in vitro results indicate that the STAMPs can inhibit CLas surrogate Rhizobium grahamii more effectively compared to AMPs, suggesting that STAMPs can achieve better inhibition of CLas, potentially via enhancing the site specificity of AMPs. [ABSTRACT FROM AUTHOR]

A commonality between viruses and cancer is their ability to seize cellular machinery to rapidly proliferate while suppressing the host's innate immune response. Using probe molecules, specific sites within the virion protein 35 (VP35) of the Marburg virus that have a high affinity to dsRNA (also known as the interferon inhibitory domain, IID), RNA-dependent RNA polymerase (RdRp), and nucleoside triphosphates (NTPs) were identified in silico. Using the dsRNA-binding site as the target, three potential drug molecules FID, CBSMA, and DOCHE were screened. We discovered that FID has a unique ability to simultaneously bind to all the three key binding domains with high affinity - a property that none of the other screened drug-like candidates possessed. The ability of FID to bind onto multiple domains of VP35 is significant since this provides the potential to thwart a viral infection from several fronts simultaneously using a single drug to combat rapidly mutating viruses. [ABSTRACT FROM AUTHOR]

The rapid geographic expansion of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the infectious agent of Coronavirus Disease 2019 (COVID-19) pandemic, poses an immediate need for potent drugs. Enveloped viruses infect the host cell by cellular membrane fusion, a crucial mechanism required for virus replication. The SARS-CoV-2 spike glycoprotein, due to its primary interaction with the human angiotensin-converting enzyme 2 (ACE2) cell-surface receptor, is considered a potential target for drug development. In this study, around 5,800 molecules were virtually screened using molecular docking. Five molecules were selected for in vitro experiments from those that reported docking scores lower than -6 kcal/mol. Imatinib, a Bcr-Abl tyrosine kinase inhibitor, showed maximum antiviral activity in Vero cells. We further investigated the interaction of imatinib, a compound under clinical trials for the treatment of COVID-19, with SARS-CoV-2 RBD, using in silico methods. Molecular dynamics simulations verified that imatinib interacts with RBD residues that are critical for ACE2 binding. This study also provides significant molecular insights on potential repurposable small-molecule drugs and chemical scaffolds for the development of novel drugs targeting the SARS-CoV-2 spike RBD.Communicated by Ramaswamy H. Sarma.