Bone morphogenetic proteins (BMPs), a subset of the transforming growth factor (TGF)- superfamily, regulate a diverse array of cellular functions during development and in the adult. BMP-9 (also known as growth and differentiation factor (GDF)-2) potently induces osteogenesis and chondrogenesis, has been implicated in the differentiation of cholinergic neurons, and may help regulate glucose metabolism. We have determined the structure of BMP-9 to 2.3 Å and examined the differences between our model and existing crystal structures of other BMPs, both in isolation and in complex with their receptors. TGF- ligands are translated as precursors, with pro-regions that generally dissociate after cleavage from the ligand, but in some cases (including GDF-8 and TGF-1, -2, and -3), the pro-region remains associated after secretion from the cell and inhibits binding of the ligand to its receptor. Although the proregion of BMP-9 remains tightly associated after secretion, we find, in several cell-based assays, that the activities of BMP-9 and BMP-9⅐pro-region complex were equivalent. Activin receptor-like kinase 1 (ALK-1), an orphan receptor in the TGF- family, was also identified as a potential receptor for BMP-9 based on surface plasmon resonance studies (BIAcore) and the ability of soluble ALK-1 to block the activity of BMP-9⅐pro-region complex in cell-based assays.Transforming growth factor  (TGF-) 1 signaling controls a wide variety of processes over the lifetime of an organism. A subset of this large and well conserved family is the group of bone morphogenetic proteins (BMPs) and growth and differentiation factors (GDFs), which regulate a diverse array of cellular functions, including differentiation, proliferation, organogenesis, axon guidance, apoptosis, and the establishment of left-right asymmetry (1-3). BMPs and GDFs are highly conserved throughout the animal kingdom, with examples ranging from Drosophila to humans. They have frequently been implicated in the treatment of bone disorders and injury, in accordance with their robust ability to generate de novo bone formation.All TGF- ligands are translated as precursor proteins, consisting of an amino-terminal pro-region and a carboxyl-terminal ligand. This precursor forms a disulfide-linked homodimer in the cytoplasm, and the pro-region is then cleaved from the ligand. In most cases, the pro-region disassociates, and the mature ligand is secreted from the cell, but the pro-regions of GDF-8 (also known as myostatin) and TGF-1, -2, and -3 remain noncovalently associated with the ligand after secretion and inhibit binding of their ligands to their respective receptors (4 -6). Transgenic mice overexpressing the pro-region of GDF-8 show dramatic increases in muscle mass, further indicating that the pro-region functionally inhibits GDF-8 (7). The proregion of BMP-9 also remains tightly associated after secretion from the cell.BMP signaling is induced when a dimeric ligand binds to the extracellular domains of two type I and two type II receptors (8). This assembl...
High throughput cDNA sequencing has led to the identification of interferon-, a novel subclass of type I interferon that displays ϳ30% homology to other family members. Interferon-consists of 207 amino acids, including a 27-amino acid signal peptide and a series of cysteines conserved in type I interferons. The gene encoding interferon-is located on the short arm of chromosome 9 adjacent to the type I interferon gene cluster and is selectively expressed in epidermal keratinocytes. Expression of interferon-is significantly enhanced in keratinocytes upon viral infection, upon exposure to double-stranded RNA, or upon treatment with either interferon-␥ or interferon-. Administration of interferon-recombinant protein imparts cellular protection against viral infection in a species-specific manner. Interferon-activates the interferon-stimulated response element signaling pathway and a panel of genes similar to those regulated by other type I interferons including anti-viral mediators and transcriptional regulators. An antibody that neutralizes the type I interferon receptor completely blocks interferon-signaling, demonstrating that interferon-utilizes the same receptor as other type I interferons. Interferon-therefore defines a novel subclass of type I interferon that is expressed in keratinocytes and expands the repertoire of known proteins mediating host defense. Interferons (IFNs)1 are a family of functionally related cytokines that confer a range of cellular responses including antiviral, antiproliferative, antitumor, and immunomodulatory activities (1, 2). They are classified as type I or type II according to their structural and functional properties. Although the sole member of the type II family is IFN-␥, there are multiple members of the type I interferon class, which is divided into the IFN-␣, IFN-, and IFN-subclasses (1, 2). In humans, excluding psuedogenes, there are 13 non-allelic IFN-␣ genes, a single  gene, and a single gene. Members of the IFN-␣ family display greater than 80% identity to each other, IFN-displays ϳ60% identity to IFN-␣, and IFN- is ϳ40% identical to the other family members. The evolutionary conservation of the type I IFN genes is reflected in their common intron-less structure and their co-localization to the short arm of chromosome 9, which suggest that type I IFNs arose by gene duplication (3). The subtypes were initially categorized further by their cell of origin. IFN-␣ and IFN-genes were thought to be produced predominantly by leukocytes and IFN- by fibroblasts. However, upon appropriate induction, most human cell types can generate type I IFNs (2). Exposure to a variety of agents triggers the rapid and transient production of type I IFNs, with viruses being the most efficient natural inducers (4, 5). Certain bacteria can also induce expression, as can double-stranded RNA (dsRNA) and endotoxin. In contrast, trophoblast IFNs or IFN-, which are found only in ruminant ungulate species, are not induced by viral challenge (6). These genes are expressed by the embryonic trophoecto...
CC chemokine ligand 14, CCL14, is a human CC chemokine that is of recent interest because of its natural ability, upon proteolytic processing of the first eight NH2-terminal residues, to bind to and signal through the human immunodeficiency virus type-1 (HIV-1) co-receptor, CC chemokine receptor 5 (CCR5). We report X-ray crystallographic structures of both full-length CCL14 and signaling-active, truncated CCL14 [9-74] determined at 2.23 and 1.8 A, respectively. Although CCL14 and CCL14 [9-74] differ in their ability to bind CCR5 for biological signaling, we find that the NH2-terminal eight amino acids (residues 1 through 8) are completely disordered in CCL14 and both show the identical mode of the dimeric assembly characteristic of the CC type chemokine structures. However, analytical ultracentrifugation studies reveal that the CCL14 is stable as a dimer at a concentration as low as 100 nM, whereas CCL14 [9-74] is fully monomeric at the same concentration. By the same method, the equilibrium between monomers of CCL14 [9-74] and higher order oligomers is estimated to be of EC1,4 = 4.98 microM for monomer-tetramer conversion. The relative instability of CCL14 [9-74] oligomers as compared to CCL14 is also reflected in the Kd's that are estimated by the surface plasmon resonance method to be approximately 9.84 and 667 nM for CCL14 and CCL14 [9-74], respectively. This approximately 60-fold difference in stability at a physiologically relevant concentration can potentially account for their different signaling ability. Functional data from the activity assays by intracellular calcium flux and inhibition of CCR5-mediated HIV-1 entry show that only CCL14 [9-74] is fully active at these near-physiological concentrations where CCL14 [9-74] is monomeric and CCL14 is dimeric. These results together suggest that the ability of CCL14 [9-74] to monomerize can play a role for cellular activation.
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