Hepcidin is a tightly folded 25-residue peptide hormone containing four disulfide bonds, which has been shown to act as the principal regulator of iron homeostasis in vertebrates. We used multiple techniques to demonstrate a disulfide bonding pattern for hepcidin different from that previously published. . NMR studies reveal a new model for hepcidin that, at ambient temperatures, interconverts between two different conformations, which could be individually resolved by temperature variation. Using these methods, the solution structure of hepcidin was determined at 325 and 253 K in supercooled water. X-ray analysis of a co-crystal with Fab appeared to stabilize a hepcidin conformation similar to the high temperature NMR structure.

The novel transmembrane aspartic protease BACE (for Beta-site APP Cleaving Enzyme) is the ␤-secretase that cleaves amyloid precursor protein to initiate ␤-amyloid formation. As such, BACE is a prime therapeutic target for the treatment of Alzheimer's disease. BACE, like other aspartic proteases, has a propeptide domain that is removed to form the mature enzyme. BACE propeptide cleavage occurs at the sequence RLPR2E, a potential furin recognition motif. Here, we explore the role of furin in BACE propeptide domain processing. BACE propeptide cleavage in cells does not appear to be autocatalytic, since an inactive D93A mutant of BACE is still cleaved appropriately. BACE and furin co-localize within the Golgi apparatus, and propeptide cleavage is inhibited by brefeldin A and monensin, drugs that disrupt trafficking through the Golgi. Treatment of cells with the calcium ionophore A23187, leading to inhibition of calcium-dependent proteases including furin, or transfection with the ␣ 1 -antitrypsin variant ␣ 1 -PDX, a potent furin inhibitor, dramatically reduces cleavage of the BACE propeptide. Moreover, the BACE propeptide is not processed in the furin-deficient LoVo cell line; however, processing is restored upon furin transfection. Finally, in vitro digestion of recombinant soluble BACE with recombinant furin results in complete cleavage only at the established E46 site. Taken together, our results strongly suggest that furin, or a furin-like proprotein convertase, is responsible for cleaving the BACE propeptide domain to form the mature enzyme.At the histopathological level, AD 1 is characterized by neurofibrillary tangles and amyloid plaques throughout the parenchyma of the brain, as well as amyloid deposits in the cerebral vasculature (reviewed in Ref.

P450c17 is the single enzyme mediating both 17a-hydroxylase (steroid 17ai-monooxygenase, EC 1.14.99.9) and 17,20 lyase activities in the synthesis of steroid hormones. It has been suggested that different P450c17 isozymes mediate these activities in the adrenal gland and testis. We sequenced 423 of the 509 amino acids (83%) of the porcine adrenal enzyme; based on this partial sequence, a 128-fold degenerate 17-mer was synthesized and used to screen a porcine adrenal cDNA library. This yielded a 380-base cloned cDNA, which in turn was used to isolate several human adrenal cDNAs. The longest of these, Xhacl7-2, is 1754 base pairs long and includes the full-length coding region, the complete 3'-untranslated region, and 41 bases of the 5'-untranslated region. This cDNA encodes a protein of 508 amino acids having a predicted molecular weight of 57,379.82. High-stringency screening of a human testicular cDNA library yielded a partial clone containing 1303 identical bases. RNA gel blots and nuclease S1-protection experiments confirm that the adrenal and testicular P450c17 mRNAs are indistinguishable. These data indicate that the testis possesses a P450c17 identical to that in the adrenal. The human amino acid sequence is 66.7% homologous to the corresponding regions of the porcine sequence, and the human cDNA and amino acid sequences are 80.1 and 70.3% homologous, respectively, to bovine adrenal P450c17 cDNA. Both comparisons indicate that a central region comprising amino acid residues 160-268 is hypervariable among these species of P450c17. Comparison of the amino acid sequence of P450c17 with two other human steroidogenic cytochromes P450 show much greater homology with P450c21 (28.9%), another microsomal enzyme, than with P450scc (12.3%), a mitochondrial enzyme.Steroid 17a-hydroxylase (steroid 17a-monooxygenase, EC 1.14.99.9) converts pregnenolone to 17-hydroxypregnenolone and converts progesterone to 17-hydroxyprogesterone. These 17-hydroxylated steroids may then be converted by 17,20-lyase to dehydroepiandrosterone and androstenedione, respectively. These latter two steroids are precursors of testosterone and estrogen synthesis while 17-hydroxyprogesterone is a key precursor of cortisol synthesis. Although steroid 17a-hydroxylase and 17,20 lyase activities can be readily distinguished by examination of circulating venous steroidal products (1, 2), studies in both the guinea pig (3) and pig (4) show that both activities reside in a single protein, P450c17. Thus, the P450c17 enzyme is a key branch point in human steroid hormone synthesis, as 17a-hydroxylase activity distinguishes between synthesis of mineralocorticoids (aldosterone) and glucocorticoids (cortisol) and as 17,20 lyase activity distinguishes between synthesis of glucocorticoids and sex steroids. P450c17 is encoded by a gene or genes now termed P45OXVII (5). P450c17 mRNA accumulation is regulated hormonally (6, 7) and developmentally (8). Like P450c21 (steroid 21-hydroxylase), P450c17 is bound to the endoplasmic reticulum and accepts electrons f...

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The cerebral deposition of amyloid ␤-peptide is an early and critical feature of Alzheimer's disease. Amyloid ␤-peptide is released from the amyloid precursor protein by the sequential action of two proteases, ␤-secretase and ␥-secretase, and these proteases are prime targets for therapeutic intervention. We have recently cloned a novel aspartic protease, BACE, with all the known properties of ␤-secretase. Here we demonstrate that BACE is an N-glycosylated integral membrane protein that undergoes constitutive N-terminal processing in the Golgi apparatus. We have used a se- , and Cys 330 -Cys 380 ). Despite the conservation of the active site residues and the 30 -37% amino acid homology with known aspartic proteases, the disulfide motif is fundamentally different from that of other aspartic proteases. This difference may affect the substrate specificity of the enzyme. Taken together, both the presence of a transmembrane domain and the unusual disulfide bond structure lead us to conclude that BACE is an atypical pepsin family member.The hallmarks of Alzheimer's disease (AD) 1 pathology are brain plaques and vascular deposits (1) consisting of the 4-kDa amyloid ␤-peptide (A␤) (2). Overproduction of the 42-amino acid form of A␤, A␤42, has been suggested to be the cause of all known cases of familial early onset AD (3), and it is assumed that A␤42 deposition plays an early and critical role in sporadic AD as well. Therefore, A␤ metabolism has attracted considerable interest. In 1987 it was shown (4) that formation of A␤ requires proteolytic cleavage of a large type I transmembrane protein, the ␤-amyloid precursor protein (APP), which is constitutively expressed in most cell types. Over the next decade the proteolytic processing of APP has been studied in great detail in a variety of systems by many groups. Taken together, these studies have shown that A␤ is generated at a low rate by most cells analyzed and that two different proteolytic activities are required for A␤ generation. First, ␤-secretase cleaves APP to generate the N terminus of A␤, and second, ␥-secretase cleaves the C terminus, leading to the release of A␤ (for review see Ref. 5). Studies with intact cells expressing APP and the endogenous secretases have led to conclusions about the properties of the ␤-and ␥-secretases, e.g. their tissue distribution, subcellular localization, substrate requirements (see e.g. Ref. 6) etc., but until recently the identity of both ␤-and ␥-secretase was unknown. This changed when we very recently identified the novel transmembrane aspartic protease BACE as the major ␤-secretase (7). Three subsequently published independent studies (8 -10) have confirmed this conclusion. Here we characterize the BACE protein. We show that BACE is an Nglycosylated integral membrane protein that undergoes constitutive N-terminal processing in the Golgi apparatus. We determine the processing and N-glycosylation sites and the disulfide bonds. Our results demonstrate that BACE is an unusual member of the pepsin family. EXPERIMENTAL PROCEDURESMat...

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The agouti-related protein gene (Agrp) plays an important role in body weight regulation. The mature human protein is a single polypeptide chain of 112 amino acid residues, consisting of an N-terminal acidic region and a unique C-terminal cysteine-rich domain. The disulfide structure of recombinant human AGRP was determined by chemical methods using partial reduction with tris(2-carboxyethyl)phosphine under acidic conditions, followed by direct alkylation with N-ethylmaleimide or fluorescein-5-maleimide. Partial reduction and alkylation provided several forms of AGRP that were modified in a stepwise fashion. The resulting proteins were characterized by peptide mapping, sequence analysis, and mass spectrometry, showing that AGRP contained a highly reducible disulfide bond, C85-C109, followed by less reactive ones, C90-C97, C74-C88, C67-C82, and C81-C99, respectively. The chemically defined disulfide connectivity of the recombinant human AGRP was homologous to that of omega-agatoxin IVB except for an additional disulfide bond, C85-C109.

Through the use of monospecific antibodies directed against hepatic cytochrome P-450j, an enzyme induced in rats treated with ethanol or isoniazid, we have purified from human liver the related cytochrome P-450 termed HLj. HLj resembles rat P-450j and P-450 LM3a, the homologous cytochrome in rabbit liver, in its NH2-terminal amino acid sequence, in being in highest concentration in liver microsome samples prepared from two patients intoxicated by ethanol and one patient given isoniazid, and in catalyzing the metabolic activation of the procarcinogen N-nitrosodimethylamine. Furthermore, each of nine human liver RNA samples contained a species of mRNA hybridizable to a cloned HLj cDNA. We conclude that HLj is related by structure, function, and some regulatory characteristics to rat P-450j and rabbit P-450 LM3a, cytochromes critical for metabolism of several clinically relevant cytotoxic and carcinogenic agents.