Crystal structure of an aromatic ring opening dioxygenase LigAB, a protocatechuate 4,5-dioxygenase, under aerobic conditions

AbstractBackground: Sphingomonas paucimobilis SYK-6 utilizes an extradiol-type catecholic dioxygenase, the LigAB enzyme (a protocatechuate 4,5-dioxygenase), to oxidize protocatechuate (or 3,4-dihydroxybenzoic acid, PCA). The enzyme belongs to the family of class III extradiol-type catecholic dioxygenases catalyzing the ring-opening reaction of protocatechuate and related compounds. The primary structure of LigAB suggests that the enzyme has no evolutionary relationship with the family of class II extradiol-type catecholic dioxygenases. Both the class II and class III enzymes utilize a non-heme ferrous center for adding dioxygen to the substrate. By elucidating the structure of LigAB, we aimed to provide a structural basis for discussing the function of class III enzymes.Results: The crystal structure of substrate-free LigAB was solved at 2.2 Å resolution. The molecule is an α2β2 tetramer. The active site contains a non-heme iron coordinated by His12, His61, Glu242, and a water molecule located in a deep cleft of the β subunit, which is covered by the α subunit. Because of the apparent oxidation of the Fe ion into the nonphysiological Fe(III) state, we could also solve the structure of LigAB complexed with a substrate, PCA. The iron coordination sphere in this complex is a distorted tetragonal bipyramid with one ligand missing, which is presumed to be the O2-binding site.Conclusions: The structure of LigAB is completely different from those of the class II extradiol-type dioxygenases exemplified by the BphC enzyme, a 2,3-dihydroxybiphenyl 1,2-dioxygenase from a Pseudomonas species. Thus, as already implicated by the primary structures, no evolutionary relationship exists between the class II and III enzymes. However, the two classes of enzymes share many geometrical characteristics with respect to the nature of the iron coordination sphere and the position of a putative catalytic base, strongly suggesting a common catalytic mechanism

Clinical Evaluation of Topical Lotion Containing 2-Aza-8-Oxohypoxanthine on Skin Barrier Function against Water Loss

A clinical study was conducted to evaluate the efficacy of 2-aza-8-oxohypoxanthine (AOH) on human skin in a double-blind, placebo-controlled, and split-face comparative trial. To this end, a topical lotion containing 0.1% of AOH and its placebo formulation were applied in 20 Japanese subjects (age: 41–58 years, average: 48.4 ± 4.7 years) to their faces daily for eight weeks. The moisture content in the stratum corneum and the trans-epidermal water loss (TEWL) were measured at the beginning of the study and after eight weeks. The results obtained upon comparing the data of the two measuring points showed that the 0.1% AOH lotion caused a statistically significant larger decrease in TEWL after eight weeks. Moreover, the 0.1% AOH lotion produced a larger increase in the moisture content in the stratum corneum after eight weeks, although there was no statistical difference between the two formulations. These results clearly indicate that AOH is effective as a cosmetic agent with a skin barrier function against water loss

The Potential of 2-aza-8-Oxohypoxanthine as a Cosmetic Ingredient

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