The threat of a pandemic outbreak of influenza virus A H5N1 has become a major concern worldwide. The nucleoprotein (NP) of the virus binds the RNA genome and acts as a key adaptor between the virus and the host cell. It, therefore, plays an important structural and functional role and represents an attractive drug target. Here, we report the 3.3‐Å crystal structure of H5N1 NP, which is composed of a head domain, a body domain, and a tail loop. Our structure resolves the important linker segments (residues 397–401, 429–437) that connect the tail loop with the remainder of the molecule and a flexible, basic loop (residues 73–91) located in an arginine‐rich groove surrounding Arg150. Using surface plasmon resonance, we found the basic loop and arginine‐rich groove, but mostly a protruding element containing Arg174 and Arg175, to be important in RNA binding by NP. We also used our crystal structure to build a ring‐shaped assembly of nine NP subunits to model the miniribonucleo‐protein particle previously visualized by electron microscopy. Our study of H5N1 NP provides insight into the oligomerization interface and the RNA‐binding groove, which are attractive drug targets, and it identifies the epitopes that might be used for universal vaccine development.—Ng, A. K.‐L., Zhang, H., Tan, K., Li, Z., Liu, J.‐h., Chan, P. K.‐S., Li, S.‐M., Chan, W.‐Y., Au, S. W.‐N., Joachimiak, A., Walz, T., Wang, J.‐H., Shaw, P.‐C. Structure of the influenza virus A H5N1 nucleoprotein: implications for RNA binding, oligomerization, and vaccine design. FASEB J. 22, 3638–3647 (2008)

Drug-resistant superbugs pose a huge threat to human health. Infections by Enterobacteriaceae producing metallo-β-lactamases (MBLs), e.g., New Delhi metallo-β-lactamase 1 (NDM-1) are very difficult to treat. Development of effective MBL inhibitors to revive the efficacy of existing antibiotics is highly desirable. However, such inhibitors are not clinically available till now. Here we show that an anti-Helicobacter pyloridrug, colloidal bismuth subcitrate (CBS), and related Bi(III) compounds irreversibly inhibit different types of MBLs via the mechanism, with one Bi(III) displacing two Zn(II) ions as revealed by X-ray crystallography, leading to the release of Zn(II) cofactors. CBS restores meropenem (MER) efficacy against MBL-positive bacteria in vitro, and in mice infection model, importantly, also slows down the development of higher-level resistance in NDM-1-positive bacteria. This study demonstrates a high potential of Bi(III) compounds as the first broad-spectrum B1 MBL inhibitors to treat MBL-positive bacterial infection in conjunction with existing carbapenems.

Human serum transferrin (hTF) binds Fe(III) tightly but reversibly, and delivers it to cells via a receptor-mediated endocytosis process. The metal-binding and release result in significant conformational changes of the protein. Here, we report the crystal structures of diferric-hTF (Fe_NFe_C-hTF) and bismuth-bound hTF (Bi_NFe_C-hTF) at 2.8 and 2.4 Å resolutions respectively. Notably, the N-lobes of both structures exhibit unique “partially-opened” conformations between those of the apo-hTF and holo-hTF. Fe(III) and Bi(III) in the N-lobe coordinate to, besides anions, only two (Tyr95 and Tyr188) and one (Tyr188) tyrosine residues, respectively, in contrast to four residues in the holo-hTF. The C-lobe of both structures are fully closed with iron coordinating to four residues and a carbonate. The structures of hTF observed here represent key conformers captured in the dynamic nature of the transferrin family proteins and provide a structural basis for understanding the mechanism of metal uptake and release in transferrin families.

Sirtuins are pivotal regulators in various cellular processes, including transcription, DNA repair, genome stability, and energy metabolism. Their functions have been generally attributed to NAD-dependent deacetylase activity. However, human SIRT5 (sirtuin 5), which has been reported to exhibit little deacetylase activity, was recently identified as an NAD-dependent demalonylase and desuccinylase. Biochemical studies suggested that the mechanism of SIRT5-catalyzed demalonylation and desuccinylation is similar to that of deacetylation catalyzed by other sirtuins. Previously, we solved the crystal structure of a SIRT5-succinyl-lysine peptide-NAD complex. Here, we present two more structures: a binary complex of SIRT5 with an H3K9 succinyl peptide and a binary complex of SIRT5 with a bicyclic intermediate obtained by incubating SIRT5-H3K9 thiosuccinyl peptide co-crystals with NAD. To our knowledge, this represents the first bicyclic intermediate for a sirtuin-catalyzed deacylation reaction that has been captured in a crystal structure, thus providing unique insights into the reaction mechanism. The structural information should benefit the design of specific inhibitors for SIRT5 and help in exploring the therapeutic potential of targeting sirtuins for treating human diseases.

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.