The newly identified mobile colistin resistant gene (mcr-1) rapidly spread among different bacterial strains and confers colistin resistance to its host, which has become a global concern. Based on sequence alignment, MCR-1 should be a phosphoethanolamine transferase, members of the YhjW/YjdB/YijP superfamily and catalyze the addition of phosphoethanolamine to lipid A, which needs to be validated experimentally. Here we report the first high-resolution crystal structure of the C-terminal catalytic domain of MCR-1 (MCR-1C) in its native state. The active pocket of native MCR-1C depicts unphosphorylated nucleophilic residue Thr285 in coordination with two Zinc ions and water molecules. A flexible adjacent active site loop (aa: Lys348-365) pose an open conformation compared to its structural homologues, suggesting of an open substrate entry channel. Taken together, this structure sets ground for further study of substrate binding and MCR-1 catalytic mechanism in development of potential therapeutic agents.

β-Lactam antibiotics are the mainstay for the treatment of bacterial infections. However, elevated resistance to these antibiotics mediated by metallo-β-lactamases (MBLs) has become a global concern.

Bacteria offer resistance to a broad range of antibiotics by activating their export channels of ATP-binding cassette transporters. These transporters perform a central role in vital processes of self-immunity, antibiotic transport and resistance. The majority of ATP-binding cassette transporters are capable of detecting the presence of antibiotics in an external vicinity and are tightly regulated by two-component systems. The presence of an extracellular loop and an adjacent location of both the transporter and two-component system offers serious assistance to induce a quick and specific response against antibiotics. Both systems have demonstrated their ability of sensing such agents, however, the exact mechanism is not yet fully established. This review highlighted the three key functions of antibiotic resistance, transport and self-immunity of ATP-binding cassette transporters and an adjacent two-component regulatory system.

Two-component systems (TCSs) are key elements in bacterial signal transduction in response to environmental stresses. TCSs generally consist of sensor histidine kinases (SKs) and their cognate response regulators (RRs). Many SKs exhibit autokinase, phosphoryltransferase and phosphatase activities, which regulate RR activity through a phosphorylation and dephosphorylation cycle. However, how SKs perform different enzymatic activities is poorly understood. Here, several crystal structures of the minimal catalytic region of WalK, an essential SK fromLactobacillus plantarumthat shares 60% sequence identity with its homologue VicK fromStreptococcus mutans, are presented. WalK adopts an asymmetrical closed structure in the presence of ATP or ADP, in which one of the CA domains is positioned close to the DHp domain, thus leading both the β- and γ-phosphates of ATP/ADP to form hydrogen bonds to the ∊- but not the δ-nitrogen of the phosphorylatable histidine in the DHp domain. In addition, the DHp domain in the ATP/ADP-bound state has a 25.7° asymmetrical helical bending coordinated with the repositioning of the CA domain; these processes are mutually exclusive and alternate in response to helicity changes that are possibly regulated by upstream signals. In the absence of ATP or ADP, however, WalK adopts a completely symmetric open structure with its DHp domain centred between two outward-reaching CA domains. In summary, these structures of WalK reveal the intrinsic dynamic properties of an SK structure as a molecular basis for multifunctionality.

Although androgen in gender disparity of COVID-19 has been implied, no direct link has been provided. Here, we applied AlphaFold multimer, bioinformatics of network pharmacology analysis, and singe cells sequencing database reanalysis to highlight specificity of Androgen receptor (AR) against Spike receptor binding protein (RBD) of SARS-CoV-2. Our data suggest that the LXXL motifs in Spike RBD are essential for AR binding. RBD LXXA mutation complex with the AR depicting slightly reduced binding energy, as LXXLL motif usually mediates nuclear receptor binding to coregulators. Moreover, AR preferred to bind a LYRL motif in specificity and interaction interface showed a lower binding ability in Omicron than in other variants (alpha, beta, gamma and delta). Importantly, RBD LYRL motif is a conserved antigenic epitope (9 residues) for T-cell response. Network analysis of AR related genes against COVID-19 database found T-cell signaling regulation, and CD8+ T cell spatial location in AR+ single cells, which is consistent with the AR binding motif LYRL in epitope function. We provided the potent mechanisms of AR binding to RBD through LYRL linking to immune response and vaccination shift. AR could be an anti-infective therapy target for anti-Omicron new lineages.