Any feedback?
Please rate this page
(literature.php)
(0/150)

BRENDA support

Literature summary extracted from

  • Moschou, P.N.; Bozhkov, P.V.
    Separases: biochemistry and function (2012), Physiol. Plant., 145, 67-76.
    View publication on PubMed

Protein Variants

EC Number Protein Variants Comment Organism
3.4.22.49 additional information generation of human cells with one hESP allele-encoding uncleavable protein and another allele harboring a single cleavage site, the cells grow slowly owing to cell cycle delay, in particular during G2/M transition, but not when it was expected, i.e. during anaphase Homo sapiens
3.4.22.49 additional information the loss-of-function of Esp1 activity in yeast cells could be complemented by the tobacco etch virus, TEV, protease, which is also able to cleave Scc1 thus promoting segregation of sister chromatids Saccharomyces cerevisiae

Inhibitors

EC Number Inhibitors Comment Organism Structure
3.4.22.49 additional information separase is kept inactive in human cells by Cdk(Cdc2)-dependent phosphorylation even when securin is degraded Homo sapiens
3.4.22.49 securin in addition to its inhibitory role, can act as a molecular chaperone of separase, essential for its proper folding Arabidopsis thaliana
3.4.22.49 securin in addition to its inhibitory role, can act as a molecular chaperone of separase, essential for its proper folding Caenorhabditis elegans
3.4.22.49 securin in addition to its inhibitory role, can act as a molecular chaperone of separase, essential for its proper folding Chlamydomonas reinhardtii
3.4.22.49 securin in addition to its inhibitory role, can act as a molecular chaperone of separase, essential for its proper folding Cryptosporidium muris
3.4.22.49 securin in addition to its inhibitory role, can act as a molecular chaperone of separase, essential for its proper folding Drosophila melanogaster
3.4.22.49 securin in addition to its inhibitory role, can act as a molecular chaperone of separase, essential for its proper folding. Securin is dispensable for the growth of normal human cells, in contrast to cancer cells, where depletion of PTTG1 leads to chromosome instability. The human separase-securin complex shows a whale-type distinct elongated pattern. In this complex, securin is thought to interact with the N-part of separase spanned by the ARM repeats. The N- to C-terminus intramolecular interaction in separase molecules is considered to be necessary for their catalytic activation, and this interaction is abolished by securin binding Homo sapiens
3.4.22.49 securin in addition to its inhibitory role, can act as a molecular chaperone of separase, essential for its proper folding Oryza sativa
3.4.22.49 securin in addition to its inhibitory role, can act as a molecular chaperone of separase, essential for its proper folding Ricinus communis
3.4.22.49 securin in addition to its inhibitory role, can act as a molecular chaperone of separase, essential for its proper folding. The first 156 amino acids of Esp1 seem imperative for the binding of securin Pds1, it interacts with other parts of Esp1 as well Saccharomyces cerevisiae
3.4.22.49 securin in addition to its inhibitory role, can act as a molecular chaperone of separase, essential for its proper folding. Interaction takes place between the N-terminus of separase and the C-terminus of securin Schizosaccharomyces pombe
3.4.22.49 securin in addition to its inhibitory role, can act as a molecular chaperone of separase, essential for its proper folding Sorghum bicolor
3.4.22.49 securin in addition to its inhibitory role, can act as a molecular chaperone of separase, essential for its proper folding Vitis vinifera

Localization

EC Number Localization Comment Organism GeneOntology No. Textmining
3.4.22.49 additional information budding yeast Esp1 is localized to the centrosomes and spindle before anaphase Saccharomyces cerevisiae
-
-
3.4.22.49 additional information human separase is associated with centrosomes but not with spindle before anaphase, featuring predominantly cytoplasmic localization in non-dividing cells Homo sapiens
-
-
3.4.22.49 additional information in fission yeast Cut1 features similar localization in the beginning of anaphase onset persisting on the spindle until mid-anaphase Schizosaccharomyces pombe
-
-

Metals/Ions

EC Number Metals/Ions Comment Organism Structure
3.4.22.49 Ca2+ the enzyme contains a Ca2+-binding EF-hand motif, which can possibly affect separase interaction with the spindle, similar to the budding yeast Esp1, or alternatively Ca2+ might be a critical component for (auto-)catalysis Arabidopsis thaliana

Natural Substrates/ Products (Substrates)

EC Number Natural Substrates Organism Comment (Nat. Sub.) Natural Products Comment (Nat. Pro.) Rev. Reac.
3.4.22.49 cohesin + H2O Drosophila melanogaster
-
 ?
-
 ?
3.4.22.49 cohesin + H2O Chlamydomonas reinhardtii
-
 ?
-
 ?
3.4.22.49 cohesin + H2O Homo sapiens
-
 ?
-
 ?
3.4.22.49 cohesin + H2O Saccharomyces cerevisiae
-
 ?
-
 ?
3.4.22.49 cohesin + H2O Schizosaccharomyces pombe
-
 ?
-
 ?
3.4.22.49 cohesin + H2O Caenorhabditis elegans
-
 ?
-
 ?
3.4.22.49 cohesin + H2O Ricinus communis
-
 ?
-
 ?
3.4.22.49 cohesin + H2O Sorghum bicolor
-
 ?
-
 ?
3.4.22.49 cohesin + H2O Oryza sativa
-
 ?
-
 ?
3.4.22.49 cohesin + H2O Vitis vinifera
-
 ?
-
 ?
3.4.22.49 cohesin + H2O Arabidopsis thaliana
-
 ?
-
 ?
3.4.22.49 cohesin + H2O Cryptosporidium muris
-
 ?
-
 ?
3.4.22.49 additional information Homo sapiens autocleavage of human separase is to be essential and results in conformational changes ?
-
 ?
3.4.22.49 Slk19 + H2O Saccharomyces cerevisiae a protein implicated in the mitotic exit via its role in the stabilization of spindle in budding yeast ?
-
 ?

Organism

EC Number Organism UniProt Comment Textmining
3.4.22.49 Arabidopsis thaliana Q5IBC5 ESP; gene AtESP
-
3.4.22.49 Caenorhabditis elegans
-
 gene Sep-1
-
3.4.22.49 Chlamydomonas reinhardtii
-
 gene ESP1
-
3.4.22.49 Cryptosporidium muris
-
 gene Separase
-
3.4.22.49 Drosophila melanogaster
-
 gene Sse/THR, Drosophila separase is encoded by two different genes: (1) Sse-encoding separase-like protein with protease domain and (2) THR (three rows) for the protein interacting with PIM (pimples), a securin homologue of Drosophila
-
3.4.22.49 Homo sapiens
-
 gene hESP
-
3.4.22.49 Oryza sativa
-
 gene Os02g0770700
-
3.4.22.49 Ricinus communis
-
 gene Separase
-
3.4.22.49 Saccharomyces cerevisiae
-
 gene ESP1
-
3.4.22.49 Schizosaccharomyces pombe
-
 gene Cut1
-
3.4.22.49 Sorghum bicolor
-
 gene XM_002454579
-
3.4.22.49 Vitis vinifera
-
 gene LOC100259948
-

Posttranslational Modification

EC Number Posttranslational Modification Comment Organism
3.4.22.49 additional information phosphorylation and potential autocleavage sites span the region of the last ARM repeats and the central unstructured region. Human separase has an N-terminal region spanned by 26 ARM repeats and separated from the two caspase-like domains, one of which is active, by the unstructured region Homo sapiens
3.4.22.49 phosphoprotein phosphorylation sites span the region of the last ARM repeats and the central unstructured region Homo sapiens
3.4.22.49 proteolytic modification during metaphase, separase is kept inactive through its binding to the chaperone securin. During anaphase, APCcdc20 cleaves securin releasing separase. Active separase cleaves itself, and the resulting N- and C-terminal fragments associate, mechanism of separase maturation during metaphase to anaphase transition Drosophila melanogaster
3.4.22.49 proteolytic modification during metaphase, separase is kept inactive through its binding to the chaperone securin. During anaphase, APCcdc20 cleaves securin releasing separase. Active separase cleaves itself, and the resulting N- and C-terminal fragments associate, mechanism of separase maturation during metaphase to anaphase transition Chlamydomonas reinhardtii
3.4.22.49 proteolytic modification during metaphase, separase is kept inactive through its binding to the chaperone securin. During anaphase, APCcdc20 cleaves securin releasing separase. Active separase cleaves itself, and the resulting N- and C-terminal fragments associate, mechanism of separase maturation during metaphase to anaphase transition Saccharomyces cerevisiae
3.4.22.49 proteolytic modification during metaphase, separase is kept inactive through its binding to the chaperone securin. During anaphase, APCcdc20 cleaves securin releasing separase. Active separase cleaves itself, and the resulting N- and C-terminal fragments associate, mechanism of separase maturation during metaphase to anaphase transition Schizosaccharomyces pombe
3.4.22.49 proteolytic modification during metaphase, separase is kept inactive through its binding to the chaperone securin. During anaphase, APCcdc20 cleaves securin releasing separase. Active separase cleaves itself, and the resulting N- and C-terminal fragments associate, mechanism of separase maturation during metaphase to anaphase transition Caenorhabditis elegans
3.4.22.49 proteolytic modification during metaphase, separase is kept inactive through its binding to the chaperone securin. During anaphase, APCcdc20 cleaves securin releasing separase. Active separase cleaves itself, and the resulting N- and C-terminal fragments associate, mechanism of separase maturation during metaphase to anaphase transition Ricinus communis
3.4.22.49 proteolytic modification during metaphase, separase is kept inactive through its binding to the chaperone securin. During anaphase, APCcdc20 cleaves securin releasing separase. Active separase cleaves itself, and the resulting N- and C-terminal fragments associate, mechanism of separase maturation during metaphase to anaphase transition Sorghum bicolor
3.4.22.49 proteolytic modification during metaphase, separase is kept inactive through its binding to the chaperone securin. During anaphase, APCcdc20 cleaves securin releasing separase. Active separase cleaves itself, and the resulting N- and C-terminal fragments associate, mechanism of separase maturation during metaphase to anaphase transition Oryza sativa
3.4.22.49 proteolytic modification during metaphase, separase is kept inactive through its binding to the chaperone securin. During anaphase, APCcdc20 cleaves securin releasing separase. Active separase cleaves itself, and the resulting N- and C-terminal fragments associate, mechanism of separase maturation during metaphase to anaphase transition Vitis vinifera
3.4.22.49 proteolytic modification during metaphase, separase is kept inactive through its binding to the chaperone securin. During anaphase, APCcdc20 cleaves securin releasing separase. Active separase cleaves itself, and the resulting N- and C-terminal fragments associate, mechanism of separase maturation during metaphase to anaphase transition Arabidopsis thaliana
3.4.22.49 proteolytic modification during metaphase, separase is kept inactive through its binding to the chaperone securin. During anaphase, APCcdc20 cleaves securin releasing separase. Active separase cleaves itself, and the resulting N- and C-terminal fragments associate, mechanism of separase maturation during metaphase to anaphase transition Cryptosporidium muris
3.4.22.49 proteolytic modification during metaphase, separase is kept inactive through its binding to the chaperone securin. During anaphase, APCcdc20 cleaves securin releasing separase. Active separase cleaves itself, and the resulting N- and C-terminal fragments associate, mechanism of separase maturation during metaphase to anaphase transition. Autocleavage of human separase is to be essential and results in conformational changes. The C-terminal fragment of human separase, which results from autocleavage, is more unstable than the N-terminal one. The C-terminal fragment, which possesses the catalytic domain of separase, is subjected to the N-end rule pathway of protein degradation. Consequently, catalytic activity of separase can persist only for a short period of time facilitating switch off of its proteolytic function upon entering anaphase Homo sapiens

Source Tissue

EC Number Source Tissue Comment Organism Textmining
3.4.22.49 additional information human separase is present in cells as a part of very large protein complex, which in addition to securin contains also Cdk and cyclin B1, both able to inhibit separase Homo sapiens
-

Substrates and Products (Substrate)

EC Number Substrates Comment Substrates Organism Products Comment (Products) Rev. Reac.
3.4.22.49 cohesin + H2O
-
 Drosophila melanogaster ?
-
 ?
3.4.22.49 cohesin + H2O
-
 Chlamydomonas reinhardtii ?
-
 ?
3.4.22.49 cohesin + H2O
-
 Homo sapiens ?
-
 ?
3.4.22.49 cohesin + H2O
-
 Saccharomyces cerevisiae ?
-
 ?
3.4.22.49 cohesin + H2O
-
 Schizosaccharomyces pombe ?
-
 ?
3.4.22.49 cohesin + H2O
-
 Caenorhabditis elegans ?
-
 ?
3.4.22.49 cohesin + H2O
-
 Ricinus communis ?
-
 ?
3.4.22.49 cohesin + H2O
-
 Sorghum bicolor ?
-
 ?
3.4.22.49 cohesin + H2O
-
 Oryza sativa ?
-
 ?
3.4.22.49 cohesin + H2O
-
 Vitis vinifera ?
-
 ?
3.4.22.49 cohesin + H2O
-
 Arabidopsis thaliana ?
-
 ?
3.4.22.49 cohesin + H2O
-
 Cryptosporidium muris ?
-
 ?
3.4.22.49 additional information autocleavage of human separase is to be essential and results in conformational changes Homo sapiens ?
-
 ?
3.4.22.49 Slk19 + H2O a protein implicated in the mitotic exit via its role in the stabilization of spindle in budding yeast Saccharomyces cerevisiae ?
-
 ?

Subunits

EC Number Subunits Comment Organism
3.4.22.49 More the human separase is composed of three domains: the tail, the trunk, and the head, structure modeling. The first two domains are spanned by Armadillo, ARM, repeats, which are composed of multiple 42 amino acid repeats and are present in the proteomes of all eukaryotic organisms. The ARM repeat domain is highly conserved right-handed super helix of ?-helices, which serves as molecular scaffold for protein-protein interactions. Phosphorylation and potential autocleavage sites span the region of the last ARM repeats and the central unstructured region. Human separase has an N-terminal region spanned by 26 ARM repeats and separated from the Homo sapiens

Synonyms

EC Number Synonyms Comment Organism
3.4.22.49 Esp1
-
 Saccharomyces cerevisiae

General Information

EC Number General Information Comment Organism
3.4.22.49 evolution separases belong to CD clan of cysteine proteases. Unlike other members of this clan, separases are large multidomain proteins with more than 1000 amino acid residues. Mode of action in vivo and mechanistic differences in mitosis between organisms, overview Drosophila melanogaster
3.4.22.49 evolution separases belong to CD clan of cysteine proteases. Unlike other members of this clan, separases are large multidomain proteins with more than 1000 amino acid residues. Mode of action in vivo and mechanistic differences in mitosis between organisms, overview Chlamydomonas reinhardtii
3.4.22.49 evolution separases belong to CD clan of cysteine proteases. Unlike other members of this clan, separases are large multidomain proteins with more than 1000 amino acid residues. Mode of action in vivo and mechanistic differences in mitosis between organisms, overview Schizosaccharomyces pombe
3.4.22.49 evolution separases belong to CD clan of cysteine proteases. Unlike other members of this clan, separases are large multidomain proteins with more than 1000 amino acid residues. Mode of action in vivo and mechanistic differences in mitosis between organisms, overview Caenorhabditis elegans
3.4.22.49 evolution separases belong to CD clan of cysteine proteases. Unlike other members of this clan, separases are large multidomain proteins with more than 1000 amino acid residues. Mode of action in vivo and mechanistic differences in mitosis between organisms, overview Ricinus communis
3.4.22.49 evolution separases belong to CD clan of cysteine proteases. Unlike other members of this clan, separases are large multidomain proteins with more than 1000 amino acid residues. Mode of action in vivo and mechanistic differences in mitosis between organisms, overview Sorghum bicolor
3.4.22.49 evolution separases belong to CD clan of cysteine proteases. Unlike other members of this clan, separases are large multidomain proteins with more than 1000 amino acid residues. Mode of action in vivo and mechanistic differences in mitosis between organisms, overview Cryptosporidium muris
3.4.22.49 evolution separases belong to CD clan of cysteine proteases. Unlike other members of this clan, separases are large multidomain proteins with more than 1000 amino acid residues. The catalytic domain of Arabidopsis separase exhibits 31 and 32% identity to the corresponding domains of human and budding yeast homologues, respectively, while the identity exceeds 50% within plant kingdom showing that the proteolytic domain of separases is the most conserved one. The sequence identity drops dramatically for the N-termini of separases. For example, the identity of the first 600 amino acid residues between Arabidopsis and Vitis vinifera separases does not exceed 39%, and it is only 30% between Arabidopsis and rice. Mode of action in vivo and mechanistic differences in mitosis between organisms, overview Arabidopsis thaliana
3.4.22.49 evolution separases belong to CD clan of cysteine proteases. Unlike other members of this clan, separases are large multidomain proteins with more than 1000 amino acid residues. The catalytic domain of Arabidopsis thaliana separase exhibits 31 and 32% identity to the corresponding domains of human and budding yeast homologues, respectively. The sequence identity drops dramatically for the N-termini of separases. Mode of action in vivo and mechanistic differences in mitosis between organisms, overview Homo sapiens
3.4.22.49 evolution separases belong to CD clan of cysteine proteases. Unlike other members of this clan, separases are large multidomain proteins with more than 1000 amino acid residues. The catalytic domain of Arabidopsis thaliana separase exhibits 31 and 32% identity to the corresponding domains of human and budding yeast homologues, respectively. The sequence identity drops dramatically for the N-termini of separases. Mode of action in vivo and mechanistic differences in mitosis between organisms, overview Saccharomyces cerevisiae
3.4.22.49 evolution separases belong to CD clan of cysteine proteases. Unlike other members of this clan, separases are large multidomain proteins with more than 1000 amino acid residues. The sequence identity exceeds 50% within plant kingdom showing that the proteolytic domain of separases is the most conserved one. The sequence identity drops dramatically for the N-termini of separases. For example, the identity of the first 600 amino acid residues between Arabidopsis thaliana and Oryza sativa is only 30%. Mode of action in vivo and mechanistic differences in mitosis between organisms, overview Oryza sativa
3.4.22.49 evolution separases belong to CD clan of cysteine proteases. Unlike other members of this clan, separases are large multidomain proteins with more than 1000 amino acid residues. The sequence identity exceeds 50% within plant kingdom showing that the proteolytic domain of separases is the most conserved one. The sequence identity drops dramatically for the N-termini of separases. For example, the identity of the first 600 amino acid residues between Arabidopsis thaliana and Vitis vinifera separases does not exceed 39%. Mode of action in vivo and mechanistic differences in mitosis between organisms, overview Vitis vinifera
3.4.22.49 malfunction human cells with one hESP allele-encoding uncleavable protein and another allele harboring a single cleavage site grow slowly owing to cell cycle delay, in particular during G2/M transition, but not when it was expected, i.e. during anaphase Homo sapiens
3.4.22.49 malfunction in the cells lacking securin Pds1, Esp1 distribution is largely restricted to the cytoplasm Saccharomyces cerevisiae
3.4.22.49 malfunction knocking down AtESP in meiocytes using RNAi unexpectedly converts the symmetric radial microtubule systems that form after telophase II into asymmetric structures partially resembling phragmoplasts Arabidopsis thaliana
3.4.22.49 malfunction loss of either APC or separase results in a failure of the transduction of the presumed polarity signal from the centrosome cortex Drosophila melanogaster
3.4.22.49 additional information human separase is present in cells as a part of very large protein complex, which in addition to securin contains also Cdk and cyclin B1, both able to inhibit separase. Securin, in addition to its inhibitory role, can act as a molecular chaperone of separase, essential for its proper folding. The human separase-securin complex shows a whale-type distinct elongated pattern. In this complex, securin is thought to interact with the N-part of separase spanned by the ARM repeats. The N- to C-terminus intramolecular interaction in separase molecules is considered to be necessary for their catalytic activation, and this interaction is abolished by securin binding Homo sapiens
3.4.22.49 additional information securin, in addition to its inhibitory role, can act as a molecular chaperone of separase, essential for its proper folding Drosophila melanogaster
3.4.22.49 additional information securin, in addition to its inhibitory role, can act as a molecular chaperone of separase, essential for its proper folding Chlamydomonas reinhardtii
3.4.22.49 additional information securin, in addition to its inhibitory role, can act as a molecular chaperone of separase, essential for its proper folding Caenorhabditis elegans
3.4.22.49 additional information securin, in addition to its inhibitory role, can act as a molecular chaperone of separase, essential for its proper folding Ricinus communis
3.4.22.49 additional information securin, in addition to its inhibitory role, can act as a molecular chaperone of separase, essential for its proper folding Sorghum bicolor
3.4.22.49 additional information securin, in addition to its inhibitory role, can act as a molecular chaperone of separase, essential for its proper folding Oryza sativa
3.4.22.49 additional information securin, in addition to its inhibitory role, can act as a molecular chaperone of separase, essential for its proper folding Vitis vinifera
3.4.22.49 additional information securin, in addition to its inhibitory role, can act as a molecular chaperone of separase, essential for its proper folding Arabidopsis thaliana
3.4.22.49 additional information securin, in addition to its inhibitory role, can act as a molecular chaperone of separase, essential for its proper folding Cryptosporidium muris
3.4.22.49 additional information securin, in addition to its inhibitory role, can act as a molecular chaperone of separase, essential for its proper folding. Interaction takes place between the N-terminus of separase and the C-terminus of securin Schizosaccharomyces pombe
3.4.22.49 additional information securin, in addition to its inhibitory role, can act as a molecular chaperone of separase, essential for its proper folding. Securin is dispensable for the growth of normal human cells. The first 156 amino acids of Esp1 seem imperative for the binding of securin Pds1, it interacts with other parts of Esp1 as well. Securin is not only a guardian of separase, but is also responsible for its translocation to the nucleus in the budding yeast Saccharomyces cerevisiae
3.4.22.49 physiological function function of separases in metaphase to anaphase transition, overview Chlamydomonas reinhardtii
3.4.22.49 physiological function function of separases in metaphase to anaphase transition, overview Caenorhabditis elegans
3.4.22.49 physiological function function of separases in metaphase to anaphase transition, overview Cryptosporidium muris
3.4.22.49 physiological function function of separases in metaphase to anaphase transition, overview. Human separase is a potential oncogene and hESP transcripts are accumulated in a large number of tumors Homo sapiens
3.4.22.49 physiological function function of separases in metaphase to anaphase transition, overview. Separase cleaves and removes the remaining centromeric cohesin. In plants, the molecular mechanisms regulating sister chromatid separation remain largely elusive Ricinus communis
3.4.22.49 physiological function function of separases in metaphase to anaphase transition, overview. Separase cleaves and removes the remaining centromeric cohesin. In plants, the molecular mechanisms regulating sister chromatid separation remain largely elusive Sorghum bicolor
3.4.22.49 physiological function function of separases in metaphase to anaphase transition, overview. Separase cleaves and removes the remaining centromeric cohesin. In plants, the molecular mechanisms regulating sister chromatid separation remain largely elusive Oryza sativa
3.4.22.49 physiological function function of separases in metaphase to anaphase transition, overview. Separase cleaves and removes the remaining centromeric cohesin. In plants, the molecular mechanisms regulating sister chromatid separation remain largely elusive Vitis vinifera
3.4.22.49 physiological function function of separases in metaphase to anaphase transition, overview. Separase cleaves and removes the remaining centromeric cohesin. In plants, the molecular mechanisms regulating sister chromatid separation remain largely elusive. AtESP plays a role in microtubule organization or cell polarity, and an additional role for AtESP beyond cohesin cleavage Arabidopsis thaliana
3.4.22.49 physiological function function of separases in metaphase to anaphase transition, overview. Separase cleaves and removes the remaining centromeric cohesin. In yeasts, separase is responsible for the removal of both arm and centromeric cohesin after its phosphorylation by Cdc5 or other Plks. Esp1 action is not limited to this stage. When securin is depleted in yeast cells, the proteolytic activity of Esp1 is no longer cell cycle regulated, while Scc1 is cleaved on schedule suggesting the existence of additional regulatory elements Saccharomyces cerevisiae
3.4.22.49 physiological function function of separases in metaphase to anaphase transition, overview. Separase cleaves and removes the remaining centromeric cohesin. In yeasts, separase is responsible for the removal of both arm and centromeric cohesin after its phosphorylation by Cdc5 or other Plks. Separase can target both centromeric cohesin and cohesin of chromosomal arms. Cohesin is implicated in transcriptional regulation in Schizosaccharomyces pombe. When securin is depleted in yeast cells, the proteolytic activity of Esp1 is no longer cell cycle regulated, while Scc1 is cleaved on schedule suggesting the existence of additional regulatory elements Schizosaccharomyces pombe
3.4.22.49 physiological function function of separases in metaphase to anaphase transition, overview. The activated APCCdc20/separase pathway plays a fundamental role in the establishment of the anterior-posterior axis Drosophila melanogaster