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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]

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]

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]