It has been suggested that a reduced pKa in the first cysteine (Cys32 in human thioredoxin) of the active-site sequence is important for modulation of the redox potential in thioredoxin. A hydrogen bond between the sulfhydryls of Cys32 and Cys35 may reduce the pKa of Cys32 and this pKa depression probably results in increased nucleophilicity of the Cys32 thiolate group. This nucleophilicity, in tum, is thought to be necessary for the role of thioredoxin in disulfide-bond reduction. The physiological role, if any, of thioredoxin dimer formation remains unknown. It is possible that dimerization may provide a mechanism for regulation of the protein, or a means of sensing oxidative stress.

N-glycosylation is critical to the function of monoclonal antibodies (mAbs) and distinguishes various systems used for their production. We expressed human mAbs in the small aquatic plant Lemna minor, which offers several advantages for manufacturing therapeutic proteins free of zoonotic pathogens. Glycosylation of a mAb against human CD30 was optimized by co-expressing the heavy and light chains of the mAb with an RNA interference construct targeting expression of the endogenous alpha-1,3-fucosyltransferase and beta-1,2-xylosyltransferase genes. The resultant mAbs contained a single major N-glycan species without detectable plant-specific N-glycans and had better antibody-dependent cell-mediated cytotoxicity and effector cell receptor binding activities than mAbs expressed in cultured Chinese hamster ovary (CHO) cells.

E. coli thioredoxin reductase has been cloned and sequenced [21,22] and its biochemical and physical properties extensively studied [23,24]. Eukaryotic thioredoxin reductases have so far been only cloned from Penicillium chrysogenum [25], Saccharomyces cerevisiae [26], and Arabidopsis thaliana [27] and they show 44-50% sequence identity to the bacterial enzyme. We now report the cloning and sequencing of a putative thioredoxin reductase from human placenta.

In a study of juvenile hormone-regulated gene expression, we isolated an anonymous cDNA representing a message that was strongly suppressed by juvenile hormone in the fat body of the cockroach Blaberus discoidais. (= conalbumin). These are generally at low levels in circulation but are prominent in secreted fluids such as milk, tears, and egg white, where by avid binding of free iron they act as bacteriostats. Finally, membrane-anchored melanotransferrin (antigen p97), though found at trace amounts in several tissues, is dramatically overexpressed in melanomas, where it may support rapid cellular proliferation.Complete sequences for several vertebrate transferrins are known (4-12). They share >35% amino acid positional identity with one another. Within each transferrin there is significant sequence identity between the N-and C-terminal halves, a feature suggestive of an ancestral intragenic duplication that has been confirmed by structural gene analysis (13). In harmony with their internal homology and bilobed tertiary structure, all of the vertebrate transferrins appropriately analyzed (with exception of melanotransferrin; ref. 14) have the capacity to bind two ferric ions per protein molecule. Crystallographic studies (15, 16) suggest that the two cleft lobes of the transferrins have identical sets of residues that serve as ligands to iron. Positions ofcysteine residues (34 average per polypeptide) are highly conserved.Although iron transport in vertebrates has been investigated intensively over recent decades, the subject has received little attention in studies of invertebrate animals. Circulating iron-binding proteins have been described from a tunicate (17), a crab (18), and a spider (19), but to date the only invertebrate transferrin that has been characterized and reported as a primary structure is from the sphinx moth, Manduca sexta (20,21). The insect glycoprotein (77 kDa, a molecular mass consistent with the transferrin superfamily) has significant (25-30%) global sequence identity with the vertebrate transferrins, with most notable similarity around the N-terminal iron-binding sites and in the positioning of cysteine residues. Its CD spectrum is highly reminiscent of human transferrin. M. sexta transferrin circulates and donates iron (20), indicating a primary role in iron transport. These features suggest that, despite having the capacity to bind only one ferric ion instead of two (reflected by absence of a complete iron-binding motif in the C-terminal half), the moth transferrin is evolutionarily related and functionally similar to the transferrins of vertebrates. The fat body (the main source of hemolymph proteins in insects) is a site of transferrin synthesis in M. sexta. This paper represents a dovetail of our interests in iron metabolism and hormonal control of gene expression in insects. It originated with isolation of an anonymous cDNA to a cockroach (Blaberus discoidalis) fat body mRNA that was, in the adult female, markedly suppressed by the sesquiterpenoid juvenile hormone (H),...

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