PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Protein Sorting Signals”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8Linked to original sources
PubMed1994

Influence of amino acid substitutions in the nisin leader peptide on biosynthesis and secretion of nisin by Lactococcus lactis.

Structural genes for small lanthionine-containing antimicrobial peptides, known as lantibiotics, encode N-terminal leader sequences which are not present in the mature peptide, but are cleaved off at some stage in the maturation process. Leader sequences of the different lantibiotics share a number of identical amino acid residues, but they are clearly different from sec-dependent protein export signal sequences. We studied the role of the leader sequence of the lantibiotic nisin, which is produced and secreted by Lactococcus lactis, by creating site-directed mutations at various positions in the leader peptide sequence. Mutations at Arg-1 and Ala-4, but not at the conserved Pro-2, strongly affected the processing of the leader sequence and resulted in the extracellular accumulation of a biologically inactive precursor peptide. Amino acid analysis and 1H NMR studies indicated that the precursor peptide with an Ala-4-->Asp mutation contained a modified nisin structural part with the (mutated) unmodified leader sequence still attached to it. The Ala-4-->Asp precursor peptide could be activated in vitro by enzymatic cleavage with trypsin, liberating nisin. These results confirmed that cleavage of the leader peptide is the last step in nisin maturation and is necessary to generate a biologically active peptide. Several mutations, i.e. Pro-2-->Gly,Pro-2-->Val, Asp-7-->Ala,Lys-9-->Leu,Ser-10-->Ala/Ser-12-->Ala and Val-11-->Asp/Val-13-->Glu in the leader peptide did not have any detectable effect on nisin production and secretion, although some of them affected highly conserved residues. When mutations were created in the -18 to -15 region of the nisin leader peptide (i.e. Phe-18-->Leu,Leu-16-->Lys,Asp-15-->Ala), no secretion or intracellular accumulation could be detected of nisin or its precursors. This suggested that these conserved residues are involved in the maturation process and may interact with lantibiotic-specific modifying enzymes.

Amino Acid Sequence↗
PubMed1989

A membrane component of the endoplasmic reticulum that may be essential for protein translocation.

We have purified a glycosylated, membrane-spanning protein of relative molecular mass approximately 34,000 (Mr approximately 34 K) from canine microsomes that appears to be essential for protein translocation across the endoplasmic reticulum (ER) as shown by the inhibitory action of antibodies directed against it and of monovalent Fab-fragments produced from them. The ER membrane contains at least as many molecules of the 34 K membrane protein as bound ribosomes. The protein can be detected immunologically in tissues of various organisms, indicating an universal function.

Animals↗
PubMed1992

Replication control of plasmid R1: RepA synthesis is regulated by CopA RNA through inhibition of leader peptide translation.

The replication frequency of plasmid R1 is post-transcriptionally controlled by an antisense RNA, CopA, that binds to the leader region in the RepA mRNA, CopT, and ultimately inhibits the synthesis of the replication initiator protein RepA. We present results demonstrating that CopA controls RepA synthesis indirectly. A reading frame for a 24 amino acid leader peptide (Tap, translational activator peptide) is located in the region between the copA and repA genes. A translational fusion between the tap and lacZ genes was used to demonstrate that tap is translated and controlled by CopA. Stop codons (UAA, UAG and UGA) introduced at three different positions within the tap gene led to a severe decrease in repA expression. Specific suppression of the stop codons reversed the effect. This indicates that tap translation is required for RepA synthesis. Phylogenetic comparisons between IncFII-like plasmids, together with previous in vitro and in vivo results (Ohman and Wagner, 1989, 1991), suggest that a stable RNA stem-loop structure sequesters the repA ribosome binding site irrespective of CopA-CopT duplex formation. The results presented here show that ribosomes translating the tap reading frame have to terminate close to the start codon of repA to permit reinitiation (direct translational coupling), and that transient disruption of the inhibitory RNA stem-loop is insufficient for activation of repA translation. The possibility that direct translational coupling is required because of a suboptimal repA RBS cannot be excluded.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacterial Proteins↗
PubMed1995

High level expression of the IL-1 receptor related T1 receptor in insect cells.

Baculovirus-dependent expression of membrane-associated and secreted, heavily modified proteins in insect cells often results in low yields. To optimize expression of T1, a heavily glycosylated receptor related to Interleukin-1 receptor type I, deletion mutants comprising either the heavily glycosylated extracellular domain or the isolated transmembrane and cytoplasmic portions of the T1 receptor were expressed from recombinant baculoviruses. As shown here, the use of a Baculovirus-derived leader sequence (GP67) in combination with an insect cell line with increased secretory capacity resulted in yields of several mg per liter (10(9) cells) of culture of both purified secretory T1 glycoprotein and membrane-associated T1 receptor.

Amino Acid Sequence↗
PubMed1995

Model structure of the Omp alpha rod, a parallel four-stranded coiled coil from the hyperthermophilic eubacterium Thermotoga maritima.

Omp alpha is an outer-membrane protein that spans the periplasmic space of the hyperthermophilic eubacterium Thermotoga maritima. The molecule contains a globular head with an apparent diameter of 8 nm and a rod-shaped tail of 40 nm length. The sequence of the globular domain is homologous to a conserved region of cell wall-bound proteins and probably attaches Omp alpha to the peptidoglycan. The sequence of the rod domain resembles that of coiled coil proteins and ends in a transmembrane segment that anchors Omp alpha to the outer membrane. We have analysed Omp alpha by scanning transmission electron microscopy (STEM) and by statistical sequence analysis methods. The Omp alpha rod is a tetramer with an unusual periodicity of hydrophobic residues close to 3.6 that differs from the 3.5 periodicity of canonical coiled coils. This is due to periodic omissions of three residues in the heptad repeat pattern ("stutters") whose effect is to locally distort the packing of hydrophobic layers in the core of the coiled coil. Residues in position alpha are shifted to occupy a position halfway between positions alpha and d (x layers) and residues in positions d and e are shifted so that both participate in core packing interactions (da layers). Such distorted layers are frequently found in helical bundles and are characteristic of helices that do not undergo supercoiling. The only homo-oligomeric coiled coil of known structure which contains x and da layers is the three-stranded coiled coil of influenza haemagglutinin. Using geometric constraints derived from this structure, we have built a model for the Omp alpha rod in which the helices have a crossing angle of less than 15 degrees and maintain a residual degree of supercoiling with a pitch of approximately 40 nm. Our analysis of distorted layers in the hydrophobic core of coiled coils and helical bundles shows that stutters must not be viewed as discontinuities but rather as a departure from the canonical "knobs-into-holes" packing that allows helices to interact at a low angle without supercoiling. Although stutters have been considered to weaken helical interactions, their occurrence in a rigid, highly thermostable coiled coil indicates that this may not be generally true. Our analysis also indicates that skips and stutters are two different conventions for describing the same underlying structural feature.

Amino Acid Sequence↗
PubMed1991

Mitochondrial protein import.

A dynamic picture of the mitochondrial protein import pathway is emerging, with conformational alteration a critical feature both preceding and following membrane translocation. The mediators of these steps of conformational alteration, as well as steps of recognition, translocation, and proteolytic cleavage, appear to be proteins. Using powerful tools of genetics and biochemistry, in years to come it should be possible to determine the precise molecular function of these proteins in mediating these novel reactions.

Animals↗
PubMed1995

Characterization of the nuclear gene encoding mitochondrial aconitase in the marine red alga Gracilaria verrucosa.

We have cloned a nuclear gene from the marine red alga Gracilaria verrucosa that encodes the complete 779 amino-acid mitochondrial aconitase (m-ACN), the first characterized from a photosynthetic organism. The N-terminal 28 deduced amino acids are predicted to constitute the mitochondrial transit peptide, the first described from a red alga. Putative transcriptional cis-acting elements were identified in the upstream untranslated region. The G. verrucosa m-ACN gene (m-ACN) is present in a single copy and is located ca. 1.5 kb upstream from the single-copy polyubiquitin gene. The single spliceosomal intron is located near the 5' end of the region encoding the mature m-ACN in precisely the same location and phase as intron 2 in Caenorhabditis elegans m-ACN; sequences at its 3' and 5' splice junctions and at the predicted lariat branch point conform well to the eukaryote consensus sequences. Multiple protein-sequence alignment of m-ACN, bacterial aconitase (b-ACN) and iron-responsive element-binding protein (IRE-BP), and phylogenetic analyses, revealed that m-ACN does not share a recent common ancestry with either b-ACN or IRE-BP.

Aconitate Hydratase↗
PubMed1994

Interdomain linkage in the polymeric hemoglobin molecule of Artemia.

Artemia has evolved the longest known concatenation of hemoglobin domains, the alpha subunit containing nine domains and the beta subunit having a similar size. Translation of the cDNA sequence of the alpha subunit reveals eight regions of inter-domain polypeptide linking together the nine heme-binding domains, together with partially analogous sequences preceding the first domain and following the last. Analysis of the structural possibilities of the linker sequences suggests how the domains may be organized in the subunit. The interdomain linker sequences were 14%-64% identical (62%-91% similar by Dayhoff substitution matrix) and approximately 14 residues in length including a consensus -Val-Asp-Pro-Val-Thr-Gly-Leu-. The linker composition resembled that of the 11 amino acid pre-A leader sequence of Petromyzon marinus (lamprey) hemoglobin V, the structure of which is known. Prediction of structure from the Artemia linker sequences indicated a nonhelical, turn-associated linker which could be modeled to the Petromyzon leader. Measurements confirmed that such a structure could support the packing of nine Artemia domains into a polymeric subunit of annular shape, two of which subunits (which can be similar or dissimilar) comprise the physiological molecule.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1989

Export of proteins across membranes: the helix reversion hypothesis.

A model is presented which explains the biological role of the leader peptide in protein export. Along the lines of this model, the conformational changes of a protein with environment serves as a general mechanism for translocation. The leader peptide in the cytoplasm takes a hairpin like conformation which reverts to an extended helix upon integration into the membrane. The essential features of this model are in accord with recent results of protein export.

Amino Acids↗
PubMed1992

The early and late processing of lysosomal enzymes: proteolysis and compartmentation.

Lysosomal enzymes are subjected to a number of modifications including carbohydrate restructuring and proteolytic maturation. Some of these reactions support lysosomal targeting, others are necessary for activation or keeping the enzyme inactive before being segregated, while still others may be adventitious. The non-segregated fraction of the enzyme is secreted and can be isolated from the medium. It is considered that the secreted lysosomal enzymes fulfill certain physiological and pathophysiological roles. By comparing the secreted and the intracellular enzymes it is possible to distinguish between the reactions that occur before and after the segregation. In this review the reactions that may influence the segregation are referred to as the early processing and those characteristic for the enzymes isolated from lysosomal compartments as the late processing. The early processing is characterized mainly by modifications of carbohydrate side chains. In the late processing, proteolytic fragmentation represents the most conspicuous changes. The review focuses on the compartmentation of the reactions and the proteolytic fragmentation of lysosomal enzyme precursors. While a plethora of proteolytic reactions are involved, our knowledge of the proteinases responsible for the particular maturation reactions remains very limited. The review points also to work with cells from patients affected with lysosomal storage disorders, which contributed to our understanding of the lysosomal apparatus.

Animals↗
PubMed1989

Predict7, a program for protein structure prediction.

We describe a program for protein sequence analysis which runs in IBM PC computers. Protein sequences are loaded from files in Mount-Conrad and Lipman-Pearson format. Seven features are analyzed: hydrophilicity, hydropathy, surface probability, side chain flexibility, antigenicity, secondary structure and N-glycosylation sites. Numeric results can be shown, printed or stored in files exportable to other programs. Graphics of up to four predictions can be displayed on the screen, printed out or plotted, with several definable options. This program has been designed to be fast, user-friendly and to be shared with the scientific community.

Algorithms↗
PubMed1991

Isolation and expression of a full-length cDNA encoding the human GM2 activator protein.

We report the construction of a cDNA clone encoding a functional GM2-activator protein. The sequence of the complete 5' end of the coding region was determined by direct nucleotide sequencing of a fragment generated by multiple RACE PCR procedures from Hela cell cDNA. Specific oligonucleotides were synthesized from these data which allowed us to produce a PCR fragment that contained the complete coding sequence of the protein. This was then cloned into a mammalian expression vector. The ability of purified hexosaminidase A (beta-N-acetylhexosaminidase, EC 3.2.1.52) to hydrolyse labeled GM2 ganglioside was enhanced 10-fold more by the addition in the assay mix of lysate from transfected COS-1 cells than by the addition of identical amounts of lysate from mock transfected cells. Direct sequencing of PCR fragments from two sources also identified three polymorphisms.

Amino Acid Sequence↗
PubMed1988

The 'molten globule' state is involved in the translocation of proteins across membranes?

Strong evidence exists that the translocation of proteins across a variety of membranes involves a non-native or denatured conformational states. On the other hand a compact state having secondary but not rigid tertiary structure and called the 'molten globule' state has been identified as being stable under mild denaturing conditions. A similar state has been shown to accumulate on the folding pathway of globular proteins. These states are compact though sufficiently expanded to include water, and they are internally mobile. It is proposed that these molten globule states may be suitable candidates for protein translocation across biological membranes.

Biological Transport↗
PubMed1994

The 'Hinge' protein of cytochrome c reductase from potato lacks the acidic domain and has no cleavable presequence.

The 'Hinge' protein of cytochrome c reductase from fungi and mammals is thought to support electron transport from cytochrome c1 to cytochrome c and was reported to be one of the most acidic proteins known. Isolation and analysis of cDNA clones of the first 'Hinge' protein from a plant source reveals that it has a surplus of basic residues in potato. While the overall identity between the deduced amino acid sequence of the potato 'Hinge' protein and the proteins from yeast and bovine is in the range of 40%, the characteristic acidic domain is lacking. Therefore the numerous theories on the function of the mitochondrial 'Hinge' protein seem not to apply for the protein from potato. Also the atypical acidic presequence of the 'Hinge' protein from fungi and mammals is absent as revealed by N-terminal sequencing of the isolated potato 'Hinge' protein. Functional implications of these results for the 'Hinge' proteins from other organisms are discussed.

Amino Acid Sequence↗
PubMed1995

Cardiolipin modulates the secondary structure of the presequence peptide of cytochrome oxidase subunit IV: a 2D 1H-NMR study.

The secondary structure of the presequence of cytochrome oxidase subunit IV (p25) was studied by circular dichroism and 2D nuclear magnetic resonance in micelles of dodecylphosphocholine (DPC) and mixed micelles of DPC and mitochondrial cardiolipin (CL). In both systems, alpha-helix formation was observed. The alpha-helix stretches from the N- to the C-terminus with a break at the proline residue at position 13. Upon introduction of CL in the DPC micellar system, an increased stability of the helix was observed around proline13 and in the C-terminal half. This observation, together with reported results on specific interactions between CL and p25, led to the proposal of a two-state equilibrium of the alpha-helical conformation of p25, modulated by CL.

Amino Acid Sequence↗