Precursor of egg white lysozyme. Amino acid sequence of an NH2-terminal extension

Isolation, characterization, kinetics, and enzymatic and nonenzymatic microbicidal activities of a novel c-type lysozyme from plasma of Schistocerca gregaria (Orthoptera: Acrididae)

A protein, designated as Sgl, showing a muramidase lytic activity to the cell wall of the Gram-positive bacterium Micrococcus lysodeikticus was isolated for the first time from plasma of Escherichia coli-immunized fifth instar Schistocerca gregaria. The isolated Sgl was detected as a single protein band, on both native- and SDS-PAGE, has a molecular weight of ∼15.7 kDa and an isoelectric point (pI) of ca 9.3 and its antiserum has specifically recognized its isolated form. Fifty-nine percentage of Sgl lytic activity was recovered in the isolated fractions and yielded ca 126-fold increase in specific activity than that of the crude. The partial N-terminal amino acid sequence of the Sgl has 55 and 40% maximum identity with Bombyx mori and Gallus gallus c-type lysozymes, respectively. The antibacterial activity against the Gram-positive and the Gram-negative bacteria were comparatively stronger than that of the hen egg white lysozyme (HEWL). The detected Sgl poration to the inner membrane that reach a maximum ability after 3 h was suggested to operate as a nonenzymatic mechanism for Gram-negative bacterial cell lysis, as tested in a permease-deficient E. coli, ML-35 strain. Sgl showed a maximal muramidase activity at pH 6.2, 30-50°C, and 0.05 M Ca(2+) or Mg(2+); and has a Km of 0.5 μg/ml and a Vmax of 0.518 with M. lysodeikticus as a substrate. The Sgl displayed a chitinase activity against chitin with a Km of 0.93 mg/ml and a Vmax of 1.63.

Encoding of human basic and glycosylated proline-rich proteins by the PRB gene complex and proteolytic processing of their precursor proteins

Proline-rich proteins (PRPs) constitute a family of about 20 members in human saliva that are encoded by six genes. Assignment of genomic DNA coding regions is complicated because of the occurrence of many alleles and the great similarity of amino acid sequences of PRPs. To overcome these problems, the nucleotide sequences of the genes encoding basic and glycosylated PRPs from one person were determined and then aligned with her previously determined protein sequences. This, together with additional protein data, has also resolved various discrepancies between corresponding protein and DNA sequences. For the first time in one person it is now possible to account for all the regions in the PRB genes encoding basic and glycosylated PRPs, and the primary structures of all secreted basic and glycosylated PRPs have been determined. Each gene encodes a precursor protein that subsequently undergoes proteolytic cleavage, thereby giving rise to the secreted proteins. The results have allowed identification of all the proteolytic cleavage sites in the precursor proteins, which all conform to a consensus cleavage site for furin. To evaluate if furin is responsible for the precursor protein cleavages, a recombinant precursor protein was synthesized by in vitro transcription translation of a PRB1 allele. The protein was shown to be correctly cleaved by furin, giving rise to the expected secreted proteins.

Synthesis of mammalian profilin in Escherichia coli and its characterization

Profilin is a G-actin binding protein that may have a role in controlling the ratio of G/F actin within the cell. To devise a way for obtaining large amounts of mammalian profilin in an active state, we transfected Escherichia coli with a plasmid containing a full-length rat spleen profilin cDNA adjacent to a promoter inducible by isopropyl thiogalactoside (IPTG). Upon induction, they synthesized a new protein of 15,000 MW constituting approximately 5% of the total cell protein. This protein bound to poly-L-proline Sepharose and could be eluted with 7 M urea, behavior similar to that exhibited by authentic profilin. The protein could be released from the bacteria in soluble form following sonication, and the profilin could then be purified to homogeneity following chromatography on Sephadex G-75 and DEAE A-50 Sephadex. The protein began with an unblocked Ala, indicating that the initiating formyl and methionine residues had been removed. The dissociation of the recombinant profilin from chicken skeletal muscle actin was characterized by a Kd of approximately 2 microM based on gel filtration analysis and actin polymerization assays. These results show that purified active mammalian profilin can be made conveniently in large quantities. This study also demonstrates the feasibility of using bacterially synthesized profilin in structure-function studies involving mutant profilins altered by site-directed mutagenesis.

Characterization of ribosomal frameshifting in HIV-1 gag-pol expression

Based on precedents from other retroviruses, the precursor of the human immunodeficiency virus (HIV-1) reverse transcriptase is predicted to be a polyprotein with a relative molecular mass (Mr) of 160,000 (160K) encoded by both the viral pol gene and the upstream gag gene. These two genes lie in different translational reading frames, with the 3' end of gag overlapping the 5' end of pol by 205 or 241 nucleotides. Thus, production of the gag-pol fusion protein would require either messenger RNA processing or translational frameshifting. The latter mechanism has been shown in the synthesis of the gag-pol proteins of two other retroviruses, Rous sarcoma virus (RSV) and mouse mammary tumour virus (MMTV). Here we report that translation of HIV-1 RNA synthesized in vitro by SP6 RNA polymerase yields significant amounts of a gag-pol fusion protein, indicating that efficient ribosomal frameshifting also occurs within the HIV-1 gag-pol overlap region. Site-directed mutagenesis and amino-acid sequencing localized the site of frameshifting to a UUA leucine codon near the 5' end of the overlap.

Determinants for protein translocation across mammalian endoplasmic reticulum. Membrane insertion of truncated and full-length prelysozyme molecules

The translocation of fragments of prelysozyme lacking varying portions of the COOH terminus of the protein is studied in comparison to full-length prelysozyme using transcription-coupled capping of RNA and subsequent translation in a wheat germ cell-free system. The fragments are generated by restricting cloned lysozyme cDNA at selected sites. We found that fragments of 102 and 74 amino acid residues could still be translocated by mammalian endoplasmic reticulum. Addition of signal-recognition particles (SRP) to the cell-free system blocked the nascent chain synthesis. The SRP-depleted membrane by itself could neither process nor translocate the prepolypeptide chain. The presence of both components was essential for processing and translocation as well as the release of the nascent chain arrest induced by SRP. However, when the size of the fragment was limited to 51 amino acids, the SRP-induced arrest, the translocation and processing failed to take place. These results define minimum length and structural requirements for translocation of the nascent chain across mammalian endoplasmic reticulum.

Hb Doha or alpha 2 beta 2[X-N-Met-1(NA1)Val----Glu]; a new beta-chain abnormal hemoglobin observed in a Qatari female

Structural analysis of a fast-moving hemoglobin variant, present in three members of a Qatari family, identified a Val----Glu substitution at position 1 (NA1) of the beta-chain. The introduction of this glutamic acid residue prevents the removal of the initiator methionine, thus extending the N-terminus by one residue to Met-Glu-His-Leu-Thr-. The methionine residue is blocked by an as yet not completely identified molecule. The presence of the variant in a heterozygote does not have clinical consequences.

Expression of chicken egg white lysozyme by Saccharomyces cerevisiae

An efficient yeast promoter was isolated using a beta-galactosidase (beta Gal) promoter probe vector. This promoter was then used to express chicken egg white lysozyme in yeast using a complete intron-free lysozyme-coding sequence constructed by in vitro recombination between a cDNA clone lacking the 5' end and the corresponding 5' end from a nuclear DNA clone. The resulting lysozyme is efficiently exported into the growth medium suggesting that the chicken signal sequence is recognized by the yeast secretion process.

Interaction of synthetic signal sequence fragments with model membranes

Peptide fragments corresponding to the signal sequence of chicken lysozyme, labelled with the fluorescent 5-dimethylaminonaphthalene-1-sulfonyl (dansyl) group have been synthesized. The emission characteristics and fluorescence polarization of the dansyl group have been used to study the interaction of signal sequence fragments with liposomes. The peptide fragments bind to liposomes and are associated with the hydrophobic core of the bilayer.

Signal sequences distinguish class II histocompatibility antigen beta chains of different loci

The signal sequences of two HLA-DR beta chains and the DR alpha chain were determined. In addition, the major part of a DC beta-chain signal sequence was also elucidated. The data were obtained by combining amino acid sequence analyses of isolated alpha and beta chains with nucleotide sequencing of four cDNA clones. All signal sequences comprise 25 amino acids or more. The two HLA-DR beta-chain signal sequences are identical and exhibit only marginal homology to the DC beta-chain signal sequence. No homology is apparent between alpha- and beta-chain signal sequences. The differences in the signal sequences of the DR and DC beta chains suggest that these sequences may be used to assign beta chains to different loci of the human major histocompatibility complex.

Signal sequences, secondary modification and the turnover of miscompartmentalized secretory proteins in Xenopus oocytes

The cytoplasm of the Xenopus oocyte can be altered by the microinjection of proteins and the regulatory responses to such perturbations can then be studied. We have investigated proteolytic systems within the oocyte which may be involved in the maintenance of the integrity of the different subcellular compartments. Thus primary translation products, made in the wheat germ system under the direction of frog liver, chicken oviduct, rat liver rapidly sedimenting endoplasmic reticulum, rat seminal vesicle, guinea pig mammary gland or honey been venom gland RNA, were injected into oocytes. Their stability in the frog cell cytosol was in general low compared to that of their processed counterparts. The latter were usually obtained by collecting the heterologous proteins exported by RNA-injected oocytes. Electrophoretic analysis of oocytes injected with particular primary and processed polypeptides permitted measurement of the stabilities of proteins differing only by the presence or absence of a detachable signal sequence, or by the presence of a specific secondary modification. The effect of the latter on protein stability appears slight. However, the presence of a detachable signal sequence destabilizes those miscompartmentalized secretory proteins which are otherwise stable. Indeed all other results are consistent with this concept for they show that primary translation products are in general much less and are never more stable than their processed counterparts. Thus we provide evidence that errors of compartmentation can be corrected in living cells and that this process is often facilitated by the properties conferred on a protein by a detachable signal sequence.

Synthesis and secretion of ovalbumin by mouse-growing oocytes following microinjection of chick ovalbumin mRNA

Mouse-growing oocytes were injected with chick ovalbumin mRNA. The oocytes were cultured for 18 h in the presence of [3H]leucine and the labeled ovalbumin was measured by immunoprecipitation. Two types of ovalbumin were precipitated by antibody to ovalbumin; one co-migrated with authentic, glycosylated ovalbumin in an 18% polyacrylamide gel and was estimated to be 45 000 D, whereas the other migrated faster with an apparent MW of 41 500 D. Both types of ovalbumin were also detected in the culture medium. This study demonstrates that mouse-growing oocytes can translate exogenous mRNA coding for a secreted protein and secrete two forms of the product.

Translation of the mRNAs coding for the major hemolymph proteins of Ceratitis capitata in cell-free system: comparison of the translatable mRNA levels to the respective biosynthetic levels of the proteins in the fat body during development

Four major hemolymph polypeptides (ceratitins) with molecular weights between 8.1 X 10(4) and 8.7 X 10(4) daltons have been identified in the fat body of late Ceratitis capitata larvae. Total fat body RNA from late larvae was translated in reticulocyte lysate, and the predominant in vitro translation products were shown to be the ceratitin precursors. The biosynthesis of these proteins during postembryonic development was studied in both tissue culture and cell-free system. Comparison of the biosynthetic patterns obtained in the two systems suggests a linear relationship between messenger concentration and protein synthesis. Three of these polypeptides show a coordinate pattern of synthesis and are immunologically related. After pupation, all four ceratitins are reabsorbed by the fat body where they accumulate.

Metabolic energy and cytoskeletal requirements for synthesis and secretion by acini from rat mammary gland-I. Ultrastructural and biochemical aspects of synthesis and release of milk proteins

1. Incubation of acini (alveoli) from lactating rat mammary gland with metabolic and cytoskeletal inhibitors produced a variety of effects on cell function. Cell viability was maintained during incubation as determined by the measurement of lactate dehydrogenase (LDH) activity in media and by light and electron microscopic examination. Caseins and whey proteins were found to be secreted by acini. 2. Addition of iodoacetate, 2,4-dinitrophenol, cyanide, cycloheximide, vinblastine or cytochalasin B inhibited both synthesis and secretion of milk proteins. Colchicine had no effect on synthesis but specifically inhibited protein secretion. Characteristic ultrastructural changes were produced by each inhibitor. 3. Uptake of 2-amino-isobutyric acid was reduced after incubation with all inhibitors except iodoacetate and dinitrophenol. Uridine incorporation was inhibited by colchicine, vinblastine, cytochalasin B and, at high concentrations, 2,4-dinitrophenol; cyanide and cycloheximide stimulated uridine incorporation. 4. Based on these results, milk protein secretion appeared to depend on continued protein synthesis and both processes were energy coupled. Microtubules and microfilaments also appeared to be involved in milk protein secretion.

Amino-terminal sequence of chicken preproalbumin

Poly(A)-containing RNA was isolated from chicken liver and translated in a reticulocyte lysate protein-synthesizing system in the presence of radiolabeled amino acids. Chicken albumin was isolated from the translation products by immunoprecipitation and subjected to automated Edman radiosequencing. Comparison with the sequence of proalbumin showed that the translocation product (preproalbumin) contains an NH2-terminal extension of 18 amino acid residues. The NH2-terminal sequence of chicken preproalbumin was as follows: Met-18-Lys-Asn-Val-15-Thr-Leu-Ile-Ser-Phe-10-Ile-Phe-Leu-Phe-Ser-5-Ser-Ala-Thr- Ser-1-Arg1, where Arg1 represents the NH2-terminal residue of proalbumin. This NH2-terminal extension is very rich in hydrophobic amino acid residues and is similar to the signal sequences found in other secreted proteins. The signal sequence of chicken preproalbumin shows considerable homology with the signal sequences of rat and bovine preproalbumins, but little homology with the signal sequences of other chicken preproteins.

Isolation and characterization of alpha-amylase messenger RNA from bank vole parotid glands. Evidence for two separate messenger RNAs coding for amylase and an amylase-related protein

Bank vole saliva contains two glycogen-precipitable proteins, both of which show affinity for the alpha-amylase inhibitor cycloheptaamylose. One of these proteins, amylase, has a molecular weight of 55,000, judged from dodecylsulphate/acrylamide gel electrophoresis. The other has an apparent molecular weight of 59,000 and has no amylase activity. We report here that tryptic peptide maps as well as amino-acid composition analyses indicate extensive homology between the two proteins. We have also isolated total poly(A)-containing mRNA from amylase-rich bank vole parotid glands. These mRNAs were translated in the presence of [35S]methionine in an mRNA-dependent cell-free translation system from rabbit reticulocyte lysate. The radioactive translation products were examined by dodecylsulphate/polyacrylamide gel electrophoresis. Two major translation products with apparent molecular weights of approximately 56,500 and 60,500, respectively, were further characterized by tryptic peptide analyses. Our data indicate that the 56,500-Mr product is the biosynthetic precursor of amylase, whereas the 60,500-Mr translation product is a precursor of the 59,000-Mr amylase-like protein. Both precursors appear to contain extra peptide material, presumably as amino-terminal 'pre' or 'signal' peptides, in analogy with that found for other precursors of secretory proteins. Thus, amylase and the 59,000-Mr protein, although very similar, are translated from two separate mRNAs. These two messengers sediment in a sucrose gradient at about 17-S, corresponding to lengths of about 1,800 nucleotides.

Polysome-dependent in vitro translation system capable of peptide chain reinitiation

A sensitive in vitro translation system has been developed which makes use of cellular polysomes as the source of mRNA and ribosomes. The soluble factors are derived from the preincubated S-30 fraction by centrifugation through a discontinuous sucrose gradient. Of the four fractions tested, fraction 1 (topmost fraction in the gradient) and fraction 2 (fraction sedimenting in 0.5 M sucrose) were stimulatory. These two fractions together yield the highest activity, corresponding to about 125 times the background incorporation. The polysome-directed system exhibits optimal activity in the range 1.8-2 mM Mg2+ and 125-175 mM KCl. The polysome-directed in vitro products exhibit a complexity comparable to the in vivo products resolved on the two-dimensional polyacrylamide gels of O'Farrell [O'Farrell, P. (1975) J. Biol. Chem. 250, 4007-4021]. The system is capable of active chain reinitiation as indicated by partial inhibition by 7-methylguanosine 5'-monophosphate and pactomycin and N-terminal end analysis of in vitro products. This system can also translate polysomes from diverse tissues such as mouse liver, rat liver, and rat brain. The levels and also the authenticity of translation of rat liver albumin and mouse liver carbamoyl phosphate synthetase I were tested by immunoprecipitation with monospecific antibodies. The results show that the major as well as the minor translation products are synthesized in this system at levels comparable to the physiological levels.

Analysis of Semliki-Forest-virus structural proteins to illustrate polyprotein processing of alpha viruses

The four structural proteins of Semliki Forest virus were purified in an amount of 30-50 nmol by preparative sodium dodecylsulfate/polyacrylamide gel electrophoresis. Each protein was subjected to N-terminal structural analysis by degradation in a liquid-phase sequencer. About 20 residues were determined for each of the two membrane glycoproteins E1 and E2. The amino acid sequence of E1 but not that of E2 showed extensive homology to the corresponding proteins of the closely related Sindbis virus. Both E1 and E2 seem to lack a signal sequence at the N terminus, since the proportion of polar amino acids in this region deviates from the proportion in the known hydrophobic signal sequences. The envelope glycoprotein E3 and the capsid protein did not yield any significant result on Edman degradation, suggesting that they have blocked N-terminal amino groups.

Isolation of Trypanosoma brucei variant specific antigen mRNA by immunoprecipitation of polysomes

The mRNA encoding the variant specific antigen of Trypanosoma brucei has been prepared by immunoprecipitation of polysomes. Polysomes carrying the variant specific antigen account for approx. 3% of the total polysomes. The mRNA thus produced is active in the mRNA dependent rabbit reticulocyte lysate in vitro protein synthesis system and directs the synthesis of a polypeptide of 60 000 daltons which co-migrates both with 125I-labelled purified variant specific antigen and with antigen immunoprecipitated from reticulocyte lysate charged with total polyadenylated mRNA from the same clone. The mRNA is being used both to prepare cDNA clones and to prepare high specific radioactivity cDNA to be used to screen a gene bank for clones containing variant specific antigen coding sequences.