Catechol oxidases are ubiquitous plant enzymes containing a dinuclear copper center. In the wound-response mechanism of the plant they catalyze the oxidation of a broad range of ortho-diphenols to the corresponding o-quinones coupled with the reduction of oxygen to water. The crystal structures of the enzyme from sweet potato in the resting dicupric Cu(II)-Cu(II) state, the reduced dicuprous Cu(I)-Cu(I) form, and in complex with the inhibitor phenylthiourea were analyzed. The catalytic copper center is accommodated in a central four-helix-bundle located in a hydrophobic pocket close to the surface. Both metal binding sites are composed of three histidine ligands. His 109, ligated to the CuA site, is covalently linked to Cys 92 by an unusual thioether bond. Based on biochemical, spectroscopic and the presented structural data, a catalytical mechanism is proposed in which one of the oxygen atoms of the diphenolic substrate binds to CuB of the oxygenated enzyme.

The expression of microRNA in nonalcoholic steatohepatitis (NASH) and their role in the genesis of NASH are not known. The aims of this study were to: (1) identify differentially expressed microRNAs in human NASH, (2) tabulate their potential targets, and (3) define the effect of a specific differentially expressed microRNA, miR-122, on its targets and compare these effects with the pattern of expression of these targets in human NASH. The expression of 474 human microRNAs was compared in subjects with the metabolic syndrome and NASH versus controls with normal liver histology. Differentially expressed microRNAs were identified by the Paraflo microRNA microarray assay and validated using quantitative real-time polymerase chain reaction (PCR). The effects of a specific differentially expressed miRNA (miR-122) on its predicted targets were assessed by silencing and overexpressing miR-122 in vitro. A total of 23 microRNAs were underexpressed or overexpressed. The predicted targets of these microRNAs are known to affect cell proliferation, protein translation, apoptosis, inflammation, oxidative stress, and metabolism. The miR-122 level was significantly decreased in subjects with NASH (63% by real-time PCR, P < 0.00001). Silencing miR-122 led to an initial increase in mRNA levels of these targets (P < 0.05 for all) followed by a decrease by 48 hours. This was accompanied by an increase in protein levels of these targets (P < 0.05 for all). Overexpression of miR-122 led to a significant decrease in protein levels of these targets. Conclusions: NASH is associated with altered hepatic microRNA expression. Underexpression of miR-122 potentially contributes to altered lipid metabolism implicated in the pathogenesis of NASH. (HEPATOLOGY 2008;48: 1810-1820.)

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The crystal structure of catechol oxidase reveals new insight into the functional properties of the type-3 copper proteins. This class of proteins includes the closely related and better-known tyrosinase as well as hemocyanin, an oxygen transport protein. All these proteins have a dinuclear copper center, have similar spectroscopic behaviors, and show close evolutionary and functional relationships. Comparison between the 3D structures of catechol oxidase and hemocyanins reveals the structural reasons for the divergence in function.

VlsE is an outer surface lipoprotein of Borrelia burgdorferi that undergoes antigenic variation through an elaborate gene conversion mechanism and is thought to play a major role in the immune response to the Lyme disease borellia. The crystal structure of recombinant variant protein VlsE1 at 2.3-Å resolution reveals that the six variable regions form loop structures that constitute most of the membrane distal surface of VlsE, covering the predominantly ␣-helical, invariant regions of the protein. The surface localization of the variable amino acid segments appears to protect the conserved regions from interaction with antibodies and hence may contribute to immune evasion.Lyme disease is a multistage, tick-borne infection that is endemic to regions of the United States, Europe, and Asia (1). The causative bacteria are a family of closely related spirochetes, including Borrelia burgdorferi, Borrelia garinii, and Borrelia afzelii, and are transmitted from one mammal to another by Ixodes ticks. Lyme disease borrelia cause persistent infections and chronic neurologic, cardiovascular, and arthralgic manifestations that can last for months to years in humans and other mammals if not treated successfully, indicating that the spirochetes can effectively evade the host's immune defenses.The mechanisms of immune evasion are not well understood at this time but are thought to include at least one form of antigenic variation. The variable major protein (VMP)-like sequence (vls) 1 locus of B. burgdorferi (2) is a complex antigenic variation system that in many ways resembles the more thoroughly characterized variable major protein system of relapsing fever borrelia (3). The vls locus of B. burgdorferi B31 consists of the expression site vlsE and a contiguous set of 15 vls silent cassettes. The exact function of the 35-kDa surfaceexposed lipoprotein VlsE is unknown; however, it is thought that the vls system may play an important role in mammalian infection because loss of the encoding linear plasmid lp28-1 results in reduced infectivity (4, 5).