Molecular cloning of human chondromodulin-I, a cartilage-derived growth modulating factor, and its expression in Chinese hamster ovary cells.

Bovine chondromodulin-I (ChM-I) purified from fetal cartilage stimulated the matrix synthesis of chondrocytes, and inhibited the growth of vascular endothelial cells in vitro. The human counterpart of this bovine growth regulating factor has not been identified. We report here the cloning of human ChM-I precursor cDNA and its functional expression in Chinese hamster ovary (CHO) cells. We first identified a genomic DNA fragment which encoded the N-terminus of the ChM-I precursor, and then isolated human ChM-I cDNA from chondrosarcoma tissue by PCR. The deduced amino acid sequence revealed that mature human ChM-I consists of 120 amino acids. In total, 16 amino acid residues were substituted in the human sequence, compared to the bovine counterpart. Almost of all the substitutions were found in the N-terminal hydrophilic domain. In the C-terminal hydrophobic domain (from Phe42 to Val120), the amino acid sequence was identical except for Tyr90, indicating a functional significance of the domain. Northern blotting and in situ hybridization indicated a specific expression of ChM-I mRNA in cartilage. We also successfully determined the cartilage-specific localization of ChM-I protein, using a specific antibody against recombinant human ChM-I. Multiple transfection of the precursor cDNA into CHO cells enabled us to isolate the mature form of human ChM-I from the culture supernatant. Purified recombinant human ChM-I stimulated proteoglycan synthesis in cultured chondrocytes. In contrast, it inhibited the tube morphogenesis of cultured vascular endothelial cells in vitro and angiogenesis in chick chorioallantoic membrane in vivo.     

Chondromodulin-I and tenomodulin: a new class of tissue-specific angiogenesis inhibitors found in hypovascular connective tissues

In tissues and/or organs of mesenchymal origin, the vasculature is usually well developed. However, there are certain hypovascular tissues that exhibit powerful anti-angiogenic resistance, implying the presence of tissue-type specific inhibitors of angiogenesis. Hyaline cartilage is one example, and several anti-angiogenic factors have been purified from cartilage. We previously identified chondromodulin-I (ChM-I) as a tissue-specific inhibitor of angiogenesis in fetal bovine cartilage. ChM-I is specifically expressed in the avascular regions of the growth-plate and cartilaginous bone rudiments in embryos. Recently, we cloned a novel type II transmembrane protein, tenomodulin (TeM), having a domain homologous to ChM-I at its C-terminus. TeM turned out to be expressed specifically in other hypovascular structures in the mesenchyme, such as the epimysium, tendon, and ligaments. In this overview, we discuss the structural characteristics of this class of anti-angiogenic molecules and their pathophysiological role in the control of vascularity.     

Cloning of a Drosophila cDNA encoding a polypeptide similar to the human insulin receptor precursor

A Drosophila cDNA clone was obtained using the human insulin receptor cDNA sequence as a probe. The 3586 bp nucleotide sequence predicted a single polypeptide of 1095 amino acid residues which showed considerable homology (35.2%) with the human insulin receptor precursor. Although the cDNA was incomplete at its 5'-terminal region, it encodes a transmembrane glycoprotein as a single precursor of a two subunit molecule having a structural architecture similar to that of the human insulin receptor precursor. The presumptive beta subunit carries a well conserved Tyr kinase domain which showed 63.5% homology with that of human insulin receptor; however the protein of the alpha subunit is only weakly conserved (25%).     

cDNA sequence and deduced amino acid sequence of the precursor of the 37-kDa inner envelope membrane polypeptide from spinach chloroplasts. Its transit peptide contains an amphiphilic alpha-helix as the only detectable structural element

We present the nucleotide sequence and the deduced amino acid sequence of a cDNA clone that encodes the entire precursor of the 37-kDa inner envelope membrane protein from spinach chloroplasts. The precursor protein consists of 344 amino acids (Mr 38,976). In vitro processing followed by radiosequence analysis of the in vitro transcribed and translated precursor protein revealed that its transit peptide consists of only 21 amino acid residues. The transit peptide has the potential to form an amphiphilic alpha-helix with a strong hydrophobic moment. It is speculated that this structural element represents an ancestral envelope-targeting domain. The in vitro synthesized precursor protein is directed to the chloroplasts and it is inserted into the envelope membrane in an ATP-dependent manner. The mature protein (323 amino acid residues, Mr 36,830) has a moderate hydrophobicity and contains only one membrane-spanning segment which is located at the C-terminus and possibly anchors the protein within the envelope membrane.     

Association of the transmembrane TGF-alpha precursor with a protein kinase complex

A variety of growth factors including transforming growth factor-alpha (TGF-alpha) are synthesized as transmembrane precursors. The short cytoplasmic domain of the transmembrane TGF-alpha precursor lacks any apparent motif associated with signal transduction. However, the sequence conservation of this cytoplasmic domain and its abundance of cysteine residues, reminiscent of the cytoplasmic domains of CD4 and CD8, suggest a biological function. In this study, we showed that transmembrane TGF-alpha was rapidly internalized after interaction with a specific antibody and that this internalization was greatly decreased when the COOH-terminal 31 amino acids were removed. Chemical cross- linking experiments revealed two associated proteins of 86 and 106 kD which coimmunoprecipitated with the TGF-alpha precursor. The association of p86 was dependent on the presence of the COOH-terminal cytoplasmic 31 amino acids of the TGF-alpha precursor, whereas p106 still remained associated when this segment was deleted. In addition, p106 was tyrosine-phosphorylated and exposed on the cell surface. The protein complex associated with transmembrane TGF-alpha displayed kinase activities towards tyrosine, serine, and threonine residues. These activities were not associated with transmembrane TGF-alpha when the COOH-terminal segment was truncated. The association of a protein kinase complex with transmembrane TGF-alpha may provide the basic elements for a "reverse" mode of signaling through the cytoplasmic domain of this growth factor, which may lead to two-directional communication during ligand-receptor interaction.     

Mutations in the membrane-spanning domain of the human immunodeficiency virus envelope glycoprotein that affect fusion activity.

A chimeric protein consisting of the human immunodeficiency virus type 1 (HIV-1) envelope protein (Env) ectodomain joined to the transmembrane and cytoplasmic-tail domains of vesicular stomatitis virus G protein lost the ability to fuse CD4+ HeLa cells yet was transported to the cell surface and cleaved normally. These results suggested some critical role of the HIV gp41 transmembrane or cytoplasmic domain in fusion. Subsequent mutagenic analysis of the HIV-1 Env transmembrane domain revealed that the sequence of amino acid residues from positions 696 to 707 of the transmembrane domain was important for fusion function but was not required for anchoring of the Env protein in the lipid bilayer or for transport to the cell surface. Further analysis indicated that the basic residues at positions 696 and 707 were critical for membrane fusion activity, as was the spacing between these residues. These results demonstrate that in addition to providing an anchoring function, the specific amino acid sequence in the transmembrane domain plays a crucial role in the membrane fusion process.     

Molecular cloning and sequence analysis of human genomic DNA encoding a novel membrane protein which exhibits a slowly activating potassium channel activity

The amino acid sequence for a novel human membrane protein that induces selective potassium permeation by membrane depolarization was deduced by molecular cloning and sequence analysis of its genomic DNA. This protein consists of 129 amino acid residues and shares several structural characteristics with the rat counterpart. These include a single putative transmembrane domain surrounded by many charged amino acid residues, two potential N-glycosylation sites at the amino-terminal portion and a single cysteine residue at the carboxyl-terminal portion. The transmembrane domain and its flanking carboxyl-terminal sequence are highly conserved between the human and rat sequences. Because the slowly activating potassium current elicited by the human protein on its expression in Xenopus oocytes is indistinguishable from that induced by the rat protein, the sequence conserved at the transmembrane domain and its following sequence should play an essential role in the induction of selective K+ permeation.     

The molecular organization of the lysostaphin gene and its sequences repeated in tandem

Summary The gene encoding lysostaphin of Staphylococcus staphylolyticus was cloned in Escherichia coli and its DNA sequence was determined. The complete coding region comprises 1440 base pairs corresponding to a precursor of 480 amino acids (molecular weight 51669). It was shown by NH₂-terminal amino acid sequence analysis of the purified extracellular lysostaphin from S. staphylolyticus that the mature lysostaphin consists of 246 amino acid residues (molecular weight 26926). Polyacrylamide gel electrophoresis revealed a similar molecular weight for the most active form. By computer analysis the secondary protein structure was predicted. It revealed three distinct regions in the precursor protein: a typical signal peptide (ca. 38 aa), a hydrophilic and highly ordered protein domain with 14 repetitive sequences (296 aa) and the hydrophobic mature lysostaphin. The lysostaphin precursor protein appears to be organized as a preprolysostaphin.Abbreviations aa amino acid(s)     

Primary structure and expression of a 24-kD vacuolar protein (VP24) precursor in anthocyanin-producing cells of sweet potato in suspension culture

A 24-kD vacuolar protein (VP24) accumulates abundantly in intravacuolar pigmented globules in anthocyanin-containing sweet potato (Ipomoea batatas) cells in suspension culture. A cDNA clone encoding VP24 was isolated from a cDNA library constructed from light-irradiated suspension-cultured cells. Sequence analysis revealed that a 2.9-kbp VP24 cDNA encodes a protein of 893 amino acid residues with a molecular mass of 96.3 kD. According to the deduced amino acid sequence of VP24 cDNA, VP24 is probably synthesized as a large precursor protein with an N-terminal extension composed of a signal peptide and a propeptide, plus the polypeptide of the mature VP24 and its C-terminal propeptide, which contains the multiple transmembrane domains. A search in the ProDom database revealed the mature VP24 domain belongs to the zinc metalloprotease family. Northern analysis revealed that the single 2.9-kb VP24 mRNA increases rapidly after light irradiation, whereas VP24 mRNA was undetectable in the dark-cultured cells or in the presence of a high concentration of 2,4-dichlorophenoxyacetic acid. Light-induced VP24 gene expression closely correlated with the accumulation of anthocyanin in the vacuoles. These results suggested that proteins derived from the VP24 precursor protein may be involved in vacuolar transport and/or accumulation of anthocyanin synthesized in the cytosol.     

Mitochondrial protein import: recognition of internal import signals of BCS1 by the TOM complex

BCS1, a component of the inner membrane of mitochondria, belongs to the group of proteins with internal, noncleavable import signals. Import and intramitochondrial sorting of BCS1 are encoded in the N-terminal 126 amino acid residues. Three sequence elements were identified in this region, namely, the transmembrane domain (amino acid residues 51 to 68), a presequence type helix (residues 69 to 83), and an import auxiliary region (residues 84 to 126). The transmembrane domain is not required for stable binding to the TOM complex. The Tom receptors (Tom70, Tom22 and Tom20), as determined by peptide scan analysis, interact with the presequence-like helix, yet the highest binding was to the third sequence element. We propose that the initial recognition of BCS1 precursor at the surface of the organelle mainly depends on the auxiliary region and does not require the transmembrane domain. This essential region represents a novel type of signal with targeting and sorting functions. It is recognized by all three known mitochondrial import receptors, demonstrating their capacity to decode various targeting signals. We suggest that the BCS1 precursor crosses the TOM complex as a loop structure and that once the precursor emerges from the TOM complex, all three structural elements are essential for the intramitochondrial sorting to the inner membrane.     

A novel trypsin-like serine protease (hepsin) with a putative transmembrane domain expressed by human liver and hepatoma cells

Recombinant clones with cDNA inserts coding for a new serine protease (hepsin) have been isolated from cDNA libraries prepared from human liver and hepatoma cell line mRNA. The total length of the cDNA is approximately 1.8 kilobases and includes a 5' untranslated region, 1251 nucleotides coding for a protein of 417 amino acids, a 3' untranslated region, and a poly(A) tail. The amino acid sequence coded by the cDNA for hepsin shows a high degree of identity to pancreatic trypsin and other serine proteases present in plasma. It also exhibits features characteristic of zymogens to serine proteases in that it contains a cleavage site for protease activation and the highly conserved regions surrounding the His, Asp, and Ser residues that participate in enzyme catalysis. In addition, hepsin lacks a typical amino-terminal signal peptide. Hydropathy analysis of the protein sequence, however, revealed a very hydrophobic region of 27 amino acids starting 18 residues downstream from the apparent initiator Met. This region may serve as an internal signal sequence and a transmembrane domain. This putative transmembrane domain could be involved in anchoring hepsin to the cell membrane and orienting it in such a manner that its carboxyl terminus, containing the catalytic domain, is extracellular.     

Amino acid sequence analysis of barley stripe mosaic viral proteins: tentative identification of viral serine proteases

Analysis of amino acid sequences of barley stripe mosaic virus (BSMV) proteins revealed the pentapeptide GDSGG, the sequence unique for catalytic centers of serine chymotrypsin-like proteases, in protein p14 encoded by open reading frame 4 of RNA beta. Computer-assisted comparisons revealed a statistically significant similarity between amino acid sequences of p14 and chymotrypsin-like proteases. The catalytic His and Asp residues tentatively identified in p14 together with the Ser residue of the GDSGG sequence, presumably, constitute the "catalytic triad" characteristic of chymotrypsin-like proteases. Based on these observations and on the presence of a potential N-proximal transmembrane domain in p14, this protein may be suggested to be a serine protease involved in processing of the replicase precursor within a membrane-bound replication complex of BSMV.     

Molecular cloning and characterization of CHM1L, a novel membrane molecule similar to chondromodulin-I

Chondromodulin-I (ChM-I) is a cartilage-specific glycoprotein that stimulates the growth of chondrocytes and inhibits the tube formation of endothelial cells. In the present study, we identified a novel ChM-I like molecule, designated ChM1L. Cloning of full length cDNAs of human, mouse, and rat ChM1L revealed that ChM1L encodes 317 amino acids novel type II transmembrane protein. ChM1L protein was expressed on the cell surface as N-glycosylated and non-N-glycosylated protein with molecular mass of 45 and 40 kDa, respectively. In adult mouse tissues, ChM1L mRNA was highly expressed in eye, skeletal muscle, and whole rib. The temporal pattern of ChM1L mRNA was examined using whole embryo at day 10 to 19 of gestation. After day 11, ChM1L mRNA was detected and its level was progressively elevated in association with development of mouse embryo. These data suggest that ChM1L is a novel membrane molecule which is similar to ChM-I that plays a regulatory role in eye, skeletal muscle, and development of embryo.     

Topogenic analysis of the human immunodeficiency virus type 1 envelope glycoprotein, gp160, in microsomal membranes

The orientation in cellular membranes of the 856 amino acid envelope glycoprotein precursor, gp160, of human immunodeficiency virus type 1 was investigated in vitro. Variants of the env gene were transcribed using the bacteriophage SP6 promoter, translated using a rabbit reticulocyte lysate, and translocated into canine pancreatic microsomal membranes. Immunoprecipitation studies of gp160 variants using antibodies specific for various gp160-derived polypeptides provided evidence that the external (cell surface) domain of gp160 begins at the mature amino terminus of the protein and continues through amino acid 665. A stop-transfer sequence (transmembrane domain) was identified in a hydrophobic region COOH-terminal to amino acid 665 and NH2-terminal to amino acid 732. Protease protection experiments demonstrated that gp160 possesses a single cytoplasmic domain COOH-terminal to residue 707. Membrane extraction studies using carbonate buffer provided evidence that the 29 amino acid hydrophobic domain (residues 512-541) of gp160 was unable to serve as a stop-transfer sequence. Finally, we propose that the cytoplasmic tail of gp160 forms a secondary association with the microsomal membranes.     

An ABC transporter homologous to TAP proteins.

Polymerase chain reaction amplification of cDNA from rat intestine revealed the expression of a novel ABC transporter, TAPL (TAP-like). Subsequently, the protein sequence was deduced from the nucleotide sequence of cDNA carrying the entire coding region. TAPL is transcribed ubiquitously in various rat tissues. The protein, with 762 amino acid residues, has potential transmembrane domains, and an ATP-binding domain in its amino and carboxyl terminal regions, respectively, and is highly homologous to TAP1 and TAP2 (transporters associated with antigen presentation/processing): pairwise comparisons with TAPL demonstrated 39 and 41% of the residues are identical, respectively. These numerical values are essentially the same as that for TAP1 and TAP2 (39%), and the hydropathy profiles of TAPL, TAP1 and TAP2 are quite similar. The similarity among these three proteins suggests that they could be derived from a common ancestral gene. Furthermore, we found that there is a potential splicing isoform, sharing the amino terminal 720 amino acid residues of TAPL.     

Molecular cloning and characterization of a putative protein kinase gene from the thermophilic fungus Thermomyces lanuginosus.

Based on the conserved amino acid sequence (DLKPEN) of serine-threonine protein kinase from several fungi, a degenerate primer was designed and synthesized. Total RNA was isolated from the thermophilic fungus Thermomyces lanuginosus. Using RACE-PCR, full-length cDNA of a putative serine-threonine protein kinase gene was cloned from T. lanuginosus. The full-length cDNA of T. lanuginosus protein kinase was 2551 bp and contained an 1806 bp open reading frame encoding a putative protein kinase precursor of 601 amino acid residues. Sequencing analysis showed that the cloned cDNA of T. lanuginosus had consensus protein kinase sequences. Conservative amino acid subdomains which most serine-threonine kinases contain can be found in the deduced amino acid sequence of T. lanuginosus putative protein kinase. Comparison results showed that the deduced amino acid sequence of T. lanuginosus putative protein kinase was highly homologous to that of Neurospora crassa dis1-suppressing protein kinase Dsk1. The putative protein kinase contained three arginine/serine-rich (SR) regions and two transmembrane domains. These showed that it might be a novel putative serine-threonine protein kinase.