Upon irradiation with elevated light intensities, the ice plant (Mesembryanthemum crystallinum) accumulates a complex pattern of methylated and glycosylated flavonol conjugates in the upper epidermal layer. Identification of a flavonol methylating activity, partial purification of the enzyme, and sequencing of the corresponding peptide fragments revealed a novel S-adenosyl-L-methionine-dependent O-methyltransferase that was specific for flavonoids and caffeoyl-CoA. Cloning and functional expression of the corresponding cDNA verified that the new methyltransferase is a multifunctional 26.6-kDa Mg 2؉ -dependent enzyme, which shows a significant sequence similarity to the cluster of caffeoyl coenzyme A-methylating enzymes. Functional analysis of highly homologous members from chickweed (Stellaria longipes), Arabidopsis thaliana, and tobacco (Nicotiana tabacum) demonstrated that the enzymes from the ice plant, chickweed, and A. thaliana possess a broader substrate specificity toward o-hydroquinone-like structures than previously anticipated for Mg 2؉ -dependent O-methyltransferases, and are distinctly different from the tobacco enzyme. Besides caffeoyl-CoA and flavonols, a high specificity was also observed for caffeoylglucose, a compound never before reported to be methylated by any plant O-methyltransferase. Based on phylogenetic analysis of the amino acid sequence and differences in acceptor specificities among both animal and plant Omethyltransferases, we propose that the enzymes from the Centrospermae, along with the predicted gene product from A. thaliana, form a novel subclass within the caffeoyl coenzyme A-dependent O-methyltransferases, with potential divergent functions not restricted to lignin monomer biosynthesis.Methylation by S-adenosyl-L-methionine (AdoMet) 1 dependent O-methyltransferases (OMTs) (EC 2.1.1) is a common modification in natural product biosynthesis. Site-specific O-methylation modulates the physiological properties of such compounds and reduces the chemical reactivity of phenolic hydroxyl groups (1). In plants, O-methylation is also required for monolignol biosynthesis and accounts for the structural differences and properties of lignin, which next to cellulose is the most prominent polymer on earth (2).Plant OMTs can be categorized into two major classes (3). Class I includes a group of low molecular weight (23,000 to 27,000) and Mg 2ϩ -dependent OMTs, whereas class II consists of higher molecular weight OMTs of about 38,000 to 43,000 that do not require Mg 2ϩ for catalytic activity. Prominent class II members include caffeic acid, flavonoid, coumarin, and alkaloid OMTs (4 -6). Within the class I OMTs, a group of small caffeoyl coenzyme A OMTs (CCoAOMTs) have been suggested to be key enzymes in the biosynthesis of monolignols, the precursors of gymnosperm and angiosperm lignins (7,8). In angiosperms, this task may also be performed by class II OMTs that are specific for caffeic acid, caffeyl aldehyde, or caffeyl alcohol (COMT) (9 -11). This apparent redundancy results in a cell-and tis...

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Obesity is a major public health concern, and complementary research strategies have been directed toward the identification of the underlying causative gene mutations that affect the normal pathways and networks that regulate energy balance. Here, we describe an autosomal-recessive morbid-obesity syndrome and identify the disease-causing gene defect. The average body mass index of affected family members was 48.7 (range = 36.7-61.0), and all had features of the metabolic syndrome. Homozygosity mapping localized the disease locus to a region in 3q29; we designated this region the morbid obesity 1 (MO1) locus. Sequence analysis identified a homozygous nonsense mutation in CEP19, the gene encoding the ciliary protein CEP19, in all affected family members. CEP19 is highly conserved in vertebrates and invertebrates, is expressed in multiple tissues, and localizes to the centrosome and primary cilia. Homozygous Cep19-knockout mice were morbidly obese, hyperphagic, glucose intolerant, and insulin resistant. Thus, loss of the ciliary protein CEP19 in humans and mice causes morbid obesity and defines a target for investigating the molecular pathogenesis of this disease and potential treatments for obesity and malnutrition.