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MalE is a maltose/maltodextrin‐binding protein (MBP) that plays a critical role in most bacterial maltose/maltodextrin‐transport systems. Previously reported wild‐type MBPs are monomers comprising an N‐terminal domain (NTD) and a C‐terminal domain (CTD), and maltose‐like molecules are recognized between the NTD and CTD and transported to the cell system. Because MBP does not undergo artificial dimerization, it is widely used as a tag for protein expression and purification. Here, the crystal structure of a domain‐swapped dimeric MalE from Salmonella enterica (named SeMalE) in complex with maltopentaose is reported for the first time, and its structure is distinct from typical monomeric MalE family members. In the domain‐swapped dimer, SeMalE comprises two subdomains: the NTD and CTD. The NTD and CTD of one molecule of SeMalE interact with the CTD and NTD of the partner molecule, respectively. The domain‐swapped dimeric conformation was stabilized by interactions between the NTDs, CTDs and linkers from two SeMalE molecules. Additionally, a maltopentaose molecule was found to be located at the interface between the NTD and CTD of different SeMalE molecules. These results provide new insights that will improve the understanding of maltodextrin‐binding MalE proteins. [ABSTRACT FROM AUTHOR]

The BioH carboxylesterase which is a typical α/β-hydrolase enzyme involved in biotin synthetic pathway in most bacteria. BioH acts as a gatekeeper and blocks the further elongation of its substrate. In the pathogen Klebsiella pneumoniae , BioH plays a critical role in the biosynthesis of biotin. To better understand the molecular function of BioH, we determined the crystal structure of BioH from K. pneumoniae at 2.26 Å resolution using X-ray crystallography. The structure of KpBioH consists of an α-β-α sandwich domain and a cap domain. B-factor analysis revealed that the α-β-α sandwich domain is a rigid structure, while the loops in the cap domain shows the structural flexibility. The active site of KpBioH contains the catalytic triad (Ser82-Asp207-His235) on the interface of the α-β-α sandwich domain, which is surrounded by the cap domain. Size exclusion chromatography shows that KpBioH prefers the monomeric state in solution, whereas two-fold symmetric dimeric formation of KpBioH was observed in the asymmetric unit, the conserved Cys31-based disulfide bonds can maintain the irreversible dimeric formation of KpBioH. Our study provides important structural insight for understanding the molecular mechanisms of KpBioH and its homologous proteins. • Crystal structure of K. pneumoniae BioH consists of an α-β-αsandwish domain and acapsubdomain. • The active site of KpBioH contains the catalytic triad (Ser82-Asp207-His235). • The Arg138, Arg142, Arg155, and Arg159 of KpBioH may play an important role in the binding of the substrates like ACP. • The Cys31-based disulfide bonds can maintain the irreversible dimeric formation of KpBioH. [ABSTRACT FROM AUTHOR]

The ZnuABC ATP-binding cassette transporter found in gram-negative bacteria has been implicated in ensuring adequate zinc import into Zn(II)-poor environments. ZinT is an essential component of ZnuABC and contributes to metal transport by transferring metals to ZnuA, which delivers them to ZnuB in periplasmic zinc recruitment. Although several structures of E. coli ZinT have been reported, its zinc-binding sites and oligomeric state have not been clearly identified. Here, we report the crystal structure of E. coli ZinT at 1.76 Å resolution. This structure contains one zinc ion in its calycin-like domain, and this ion is coordinated by three highly conserved histidine residues (His167, His176 and His178). Moreover, three oxygen atoms (O 1 , O 6 and O 7 ) from the citrate molecule interact with zinc, giving the zinc ion stable octahedral coordination. Our EcZinT structure shows the fewest zinc ions bound of all reported EcZinT structures. Crystallographic packing and size exclusion chromatography suggest that EcZinT prefers to form monomers in solution. Our results provide insights into the molecular function of ZinT. [ABSTRACT FROM AUTHOR]

Pyridoxal 5′-phosphate (PLP) is the active form of vitamin B6, but it is highly reactive and poisonous in its free form. YggS is a PLP-binding protein found in bacteria and humans that mediates PLP homeostasis by delivering PLP to target enzymes or by performing a protective function. Several biochemical and structural studies of YggS have been reported, but the mechanism by which YggS recognizes PLP has not been fully elucidated. Here, we report a functional and structural analysis of YggS from Fusobacterium nucleatum (FnYggS). The PLP molecule could bind to native FnYggS, but no PLP binding was observed for selenomethionine (SeMet)-derivatized FnYggS. The crystal structure of FnYggS showed a type III TIM barrel fold, exhibiting structural homology with several other PLP-dependent enzymes. Although FnYggS exhibited low (<35%) amino acid sequence similarity with previously studied YggS proteins, its overall structure and PLP-binding site were highly conserved. In the PLP-binding site of FnYggS, the sulfate ion was coordinated by the conserved residues Ser201, Gly218, and Thr219, which were positioned to provide the binding moiety for the phosphate group of PLP. The mutagenesis study showed that the conserved Ser201 residue in FnYggS was the key residue for PLP binding. These results will expand the knowledge of the molecular properties and function of the YggS family. [ABSTRACT FROM AUTHOR]

Siderophores acquire iron from hosts under iron-limiting conditions and play an essential role in the survival of microorganisms. Siderophore-interacting proteins (SIPs) from microbes release iron from the siderophore complex by reducing ferric iron to ferrous iron, but the molecular mechanism of iron reduction remains unclear. To better understand the molecular mechanism of SIPs, we herein report the crystal structure of Aeromonas hydrophila SIP (AhSIP) in complex with flavin adenine dinucleotide (FAD) as a cofactor. AhSIP consists of an N-terminal FAD binding domain and a C-terminal NADH binding domain, which are connected by a linker region. AhSIP showed unique structural differences in the orientation of the cofactor binding lobes when compared with SIP homologs. This study identified a cluster of three basic residues (Lys48, His259 and Arg262) in AhSIP distributed around a potential substrate binding pocket. In addition, AhSIP, containing the NADH binding motif E(L)VL-X 3 -GE, belongs to the group I subfamily. Our results show the diverse cofactor and substrate binding sites of the SIP family. • Crystal structure determination of the Siderophore-interacting protein SIP-FAD complex from A. hydrophila. • AhSIP consist of N-terminal FAD binding domain and C-terminal NADH binding domain. • The potential substrate binding pocket of AhSIP and putative NADH binding sites are proposed. [ABSTRACT FROM AUTHOR]

Abstract The nicotinamidase/pyrazinamidase PncA is a member of a large family of hydrolase enzymes that catalyze the deamination of nicotinamide to nicotinic acid. PncA also functions as a pyrazinamidase in a wide variety of eubacteria and is an essential coenzyme in many cellular redox reactions in living systems. We report the crystal structure of substrate-free PncA from Bacillus subtilis (BsPncA) at 2.0 Å resolution to improve our understanding of the PncA family. The structure of BsPncA consists of an α/β domain and a subdomain. The subdomain of BsPncA has a different conformation than that of PncA enzymes from other organisms. The B-factor analysis revealed a rigid structure of the α/β domain, while the subdomain is highly flexible. Both dimers and tetramers were observed in BsPncA protein crystals, but only dimers were observed in solution. Our results provide useful information that will further enhance our understanding of the molecular functions of PncA family members. Highlights • Crystal structure of B. Subtilis PncA consists of an α/β domain and a subdomain. • The metal-binding site of BsPncA is located at the bottom of a large cavity between the core and the subdomain. • Zinc ion is pentahedrally coordinated within several highly conserved amino acid residues and one water molecule. • Both dimers and tetramers were observed in BsPncA protein crystals, but only dimers were observed in solution. [ABSTRACT FROM AUTHOR]

Bacillus possesses the peptide toxin porulation-elaying rotein (SDP), which can kill cells within a biofilm to support continued growth, thereby delaying the onset of biofilm sporulation. The four-component transporter YknWXYZ acts as a major SDP efflux pump to protect cells against the endogenous SDP toxin, for which YknYZ is a non-canonical ATP-binding cassette (ABC)-type transporter. YknYZ consists of the following two components: (1) an individual protein (YknY) and (2) a respective permease (YknZ). To date, the crystal structure, molecular function, and mechanism of action of the integral membrane protein YknZ remain to be elucidated. In this study, to characterize the structural and biochemical roles of YknZ in the functional assembly of YknWXYZ, we predicted and overexpressed the YknZ extracellular domain. We determined the crystal structure of B. amyloliquefaciens YknZ at a resolution of 2.0 Å. The structure revealed that the YknZ extracellular region exhibits significant structural similarity with the MacB periplasmic domain, which is a non-canonical ABC-type transporter in the tripartite macrolide-specific efflux pump in Gram-negative bacteria. We also found that the YknZ extracellular domain can directly bind to an extracellular component of YknX. This structural and biochemical study provides insights into the assembly of YknWXYZ, which may be relevant to understanding cannibalistic peptide toxin resistance in Bacillus and controlling bacterial growth. [ABSTRACT FROM AUTHOR]

Two novel Co (II) MOFs based on 5-(4-(imidazolyl-1-yl)phenyl) isophthalic acid (H 2 L), namely [Co(L)(tib)(H 2 O) 2 ] n (CP 1) and [Co(L)(bip) 0.5 ] n (CP 2) (tib ​= ​1,3,5-tirs (1-imidazolyl) benzene, bip ​= ​3,5-bis(1-imidazolyl) pyridine ether) have been synthesized under solvothermal conditions and characterized by powder X-ray diffraction, single crystal X-ray diffraction. The photodegradation studies demonstrate that CPs 1 – 2 show high-efficiency degradation of MV (Methyl violet), and the mechanism studies demonstrate that the main active species are ⋅OH radicals. Meanwhile, electrochemistry studies demonstrate that CPs 1 – 2 can catalyze water oxidation under alkaline conditions, and CPs 1 – 2 only need the overpotential of 348 ​mV–760 mV to deliver the current density of 1 ​mA ​cm−2. Two novel Co (II) MOFs (CP 1 and CP 2) have been synthesized by H 2 L, tib, and bip. The photodegradation studies demonstrate that CPs 1-2 show high-efficiency degradation of MV. Simultaneously, electrochemistry studies show that CPs 1-2 could catalyze water oxidation with relatively low overpotential. [Display omitted] • Two novel Co-based MOFs were synthesized by solvothermal method. • Exhibit efficient photocatalytic degradation abilities towards MV/MB in aqueous solution. • Only need the overpotential of 348 ​mV–760 mV to deliver the current density of 1 ​mA ​cm−2. [ABSTRACT FROM AUTHOR]

In this work, five novel Cd/Zn-based MOFs with different topological framework, namely {[Cd(bimb)(Hbipa)]·H 2 O} n (1), {[Cd 3 (dimb) 3 (bipa) 2 (H 2 O) 2 ·2H 2 O} n (2) , [Cd(bimd)(Hbipa)(H 2 O)] n (3) , {[Zn(bipd)(Hbipa)]·H 2 O} n (4) and [Zn(bimb)(Hbipa)] n (5) had been synthesized and characterized. Worth noting, Complex 1 and 2 had effective separation behaviors towards MO and MBE dyes respectively, which could reach the adsorption equilibrium within a quite short time even if there existed another kind of dye in the system. Meanwhile, Complex 3 – 5 showed great performance in CR adsorption. Additionally, Complex 3 – 5 also showed excellent photocatalytic degradation capabilities toward MB and MV dyes under UV irradiation. According to the study, these five metal-organic frameworks can be used as a kind of functional materials in the adsorption and photocatalytic degradation of organic dyes in wastewater. [Display omitted] • Produce novel Cd/Zn -based MOFs that possess novel 3D structure. • Selectively absorb specific aromatic dyes in a mixed aqueous system. • Exhibit efficient photocatalytic degradation abilities towards MB/MV in aqueous solution. [ABSTRACT FROM AUTHOR]

[Display omitted] • Produce two novel Zn-based MOFs under solvothermal conditions. • Both of Zn-based MOFs possess analogous layered stacked structure. • Selectively absorb specific aromatic dyes in a mixed aqueous system. • Exhibit efficient photocatalytic degradation abilities towards MB/MV in aqueous solution. Two novel Zn-MOFs constructed from 5-hydroxy-2-nitroisophthalic acid (H 2 DIPA) and 5-(4-carboxy-2-nitrophenoxy)-2-nitroisophthalic acid (H 3 BPPA), namely: {[Zn 2 (DIPA) 2 (bimp) 5 ]·DMF·2H 2 O} n (Zn-MOF 1), {[Zn 2 (HBPPA) 2 (bibp) 2 ]·2H 2 O} n (Zn-MOF 2) (bimp = 1,4-di(1H-imidazol-1-yl)butane, bibp = 4,4′-bis(imidazolyl) biphenyl), have been synthesized under solvothermal conditions and characterized by single crystal X-ray diffraction, elemental analysis, IR spectra, powder X-ray diffraction (PXRD) and thermogravimetric analysis (TG). The single-crystal X-ray diffraction analysis indicates that Zn-MOF 1 exhibits an uncommon 3-nodal framework with a (4·6·8)(4·63·82)(66) topology, whereas Zn-MOF 1 exhibits an uninodal 4-connected framework with a (44·62) topology. Moreover, both of the two Zn-MOFs exhibit exceptional dye adsorption capacities towards the organic dyes with high adsorption rates and excellent adsorption amounts. Particularly, Zn-MOF 1 can selectively adsorb the cationic dye malachite green (MG) whereas Zn-MOF 2 adsorb the anionic dye methyl orange (MO) when there exists another kind of dye in the system. The adsorption process can be illustrated by pseudo-second order kinetic and Langmuir isotherm, and the feasible adsorption mechanism could be the electrostatical interactions, hydrogen bonding between the MOFs and the dyes. Meanwhile, the two Zn-MOFs also show good photocatalytic degradation capabilities toward MB/MV dyes under UV irradiation, and the mechanism studies demonstrate that the main active species are ·OH radicals. Therefore, this functional MOF materials can be treated as a convenient and cost-efficient solution for the sewage handling and environmental protection. [ABSTRACT FROM AUTHOR]

[Display omitted] • Produce novel Co-based MOFs that possess analogous layered stacked structure. • Require only 1.2 V@2.93 mA cm−2 and 1.5 V@2.78 mA cm−2 for full water splitting. • Exhibit efficient photocatalytic degradation abilities towards MB/MV in aqueous solution. Two novel Co-MOFs constructed from aromatic polycarboxylic acid named {[Co(tib) 2 (bimb) 2 ]·4H 2 O} n (tib = 3-((4-(1H-1,2,4-triazol-1-yl)benzyl)oxy)benzoic acid, bimb = 1,4-bis(imidazole-1-ylmethy) benzene) and {[Co 2 (bipa) 4 (bibp) 6 ]} n (bipa = 2-(4-carboxy-2-nitrophenoxy)-6-nitroterephthalic acid, bibp = 4,4′-bis(imidazolyl) biphenyl), have been synthesized under solvothermal conditions and characterized by single-crystal X-ray diffraction, elemental analysis, IR spectra, powder X-ray diffraction (PXRD), thermogravimetric analysis (TG) as well as electrochemistry. The single-crystal X-ray diffraction analysis indicates that Co-MOF 1 exhibits an uninodal net with a (65·8) topology, whereas Co-MOF 2 exhibits an uninodal 4-connected framework with a (44·62) topology. The electrochemistry studies demonstrate that both of the two Co-MOFs can behave as the efficient electrocatalysts for water oxidation in a mild neutral system at the potential around 1.20 V vs. NHE with comparatively low overpotential (η) for Co-MOF 1 and 2 of 337–541 mV vs. NHE. Moreover, the two Co-MOFs also show good photocatalytic degradation capabilities toward MB/MV dyes under UV irradiation, and the mechanism studies demonstrate that the main active species are · OH radicals. Therefore, these bi-functional Co-MOFs materials can be treated as convenient and efficient catalysts for the oxygen evolution reaction and aromatic dyes degradation. [ABSTRACT FROM AUTHOR]