ABSTRACTcDNAs for glutathione-independent prostaglandin D synthase were isolated from cDNA libraries of human brain. The longest cDNA insert was 837 base pairs long and contained a coding region of 570 base pairs corresponding to 190 amino acid residues with a calculated Mr of 21,016. Between two cDNA inserts isolated from the two different libraries, nucleotide substitutions were observed at 16 positions, including conservative amino acid substitutions at 2 positions and nonconservative substitutions at 5 positions, indicating genetic heterogeneity of this enzyme in humans. The computer-assisted homology search revealed that the enzyme is a member of the lipocalin superfamily, comprising secretory hydrophobic molecule transporters, showing the greatest homology (28.8-29.4% identity; 51.3-53.1% similarity) to a1-microglobulin among the members of this superfamily. In a phylogenetic tree of the superfamily, this enzyme, a,-microglobulin, and the y chain of the complement component C8 form a cluster separate from the other 14 members. The two distinctive characteristics of glutathione-independent prostaglandin D synthase, as compared to the other members ofthis superfamily, are its enzymatic properties and its association with membranes that were probably acquired after evolutionary divergence of the two lipocalins. Based on the observed sequence homology, the tertiary structure of the enzyme was deduced to consist of an eight-stranded anti-parallel ,B-barrel forming a hydrophobic pocket. Furthermore, the Cys-65 residue in the pocket, which is conserved only in the human and rat enzymes but not in other lipocalins, was considered to be a putative active site of the enzyme.Prostaglandin (PG) D2 is a major PG in rat brain and shows several central actions in vivo such as sleep induction, regulation of body temperature, anticonvulsion, suppression of luteinizing hormone release, nociception, and modulation of odor responses. In vitro it also regulates the growth and differentiation of rat glioma C6BU-1 cells and induces Ca2+ influx and cGMP formation in mouse neuroblastoma-rat glioma hybrid NG108-15 cells (for reviews, see refs. 1 and 2). In brief, PGD2 functions as a neuromodulator and/or trophic factor in the central nervous system. Glutathione (GSH)-independent PGD synthase [prostaglandin-H2 D-isomerase; (5Z,13E)-(15S)-9a,11a-epidioxy-15-hydroxyprosta-5,13-dienoate D-isomerase, EC 5.3.99.2] catalyzes the conversion of PGH2 to PGD2 in the presence of various sulfhydryl compounds (3). This enzyme is responsible for biosynthesis of PGD2 in the brain, while several other enzymes, such as GSH-requiring PGD synthase and GSH S-transferase, also catalyze the reaction to produce PGD2 and are present in various other rat tissues (4). The enzyme is localized in the central nervous system (4) and associated tissues, such as the retina (5) and cochlea (6). Furthermore, postnatal changes in the cellular localization of this enzyme have been observed in the brain (7) and cochlea (6). For example, the enzyme is distributed in m...

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Of the molecular species of proteins associated with the nucleoids of Escherichia coli cells, those with relatively high affinity to bind to DNA were isolated and characterized. Seven classes of nucleoid proteins with molecular weights of 9,000, 17,000 (two molecular species), 22,000, 24,000, 27,000 and 28,000 were isolated at more than 90% purity or were partially purified. On the basis of its amino acid composition and other chemical properties, the 9,000 dalton protein was identified as HLP II (or HU protein or BH2) (Pettijohn 1982; Rouvière-Yaniv and Gros 1975; Varshavsky et al. 1978). The 17 K protein consisted of two molecular species and one of these, 17 K (a) protein, seemed to be identical with HLPI (or protein 1 or BH1) reported previously (Pettijohn 1982; Varshavsky et al. 1977; Varshavsky et al. 1978). The 26 K protein was identical to the 22 K protein (Kishi et al. 1982). The 27 K protein showed immunological cross-reactivity with the antibody for histone H2A and was thus identified as the H protein reported previously (Hübscher et al. 1980). Two basic proteins, 9 K and 17 K(a), showed relatively high binding affinities to DNA, while the 28 K protein showed moderate binding affinity. The biological significance of these nucleoid proteins, which constitute a family of proteins participating in formation of the nucleoid structure, is discussed.

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