Seven different, but highly conserved 14-3-3 proteins are involved in diverse signaling pathways in human cells. It isunclear how the 14-3-3σ isoform, a transcriptional target of p53, exerts its inhibitory effect on ...Seven different, but highly conserved 14-3-3 proteins are involved in diverse signaling pathways in human cells. It isunclear how the 14-3-3σ isoform, a transcriptional target of p53, exerts its inhibitory effect on the cell cycle in thepresence of other 14-3-3 isoforms, which are constitutively expressed at high levels. In order to identify structuraldifferences between the 14-3-3 isoforms, we solved the crystal structure of the human 14-3-3σ protein at a resolutionof 2.8 ? and compared it to the known structures of 14-3-3ζ and 14-3-3τ. The global architecture of the 14-3-3σ foldis similar to the previously determined structures of 14-3-3ζ and 14-3-3τ: two 14-3-3σ molecules form a cup-shapeddimer. Significant differences between these 14-3-3 isoforms were detected adjacent to the amphipathic groove, whichmediates the binding to phosphorylated consensus motifs in 14-3-3-ligands. Another specificity determining region islocalized between amino-acids 203 to 215. These differences presumably select for the interaction with specific ligands,which may explain the different biological functions of the respective 14-3-3 isoforms. Furthermore, the two 14-3-3σmolecules forming a dimer differ by the spatial position of the ninth helix, which is shifted to the inside of the ligandinteraction surface, thus indicating adaptability of this part of the molecule. In addition, 5 non-conserved residues arelocated at the interface between two 14-3-3σ proteins forming a dimer and represent candidate determinants of homo-and hetero-dimerization specificity. The structural differences among the 14-3-3 isoforms described here presumablycontribute to isoform-specific interactions and functions.展开更多
Different from canonical ubiquitin-like proteins, Hub1 does not form covalent conjugates with substrates but binds proteins noncovalently. In Socchoromyces cerevisioe, Hub1 associates with spUceosomes and mediates alt...Different from canonical ubiquitin-like proteins, Hub1 does not form covalent conjugates with substrates but binds proteins noncovalently. In Socchoromyces cerevisioe, Hub1 associates with spUceosomes and mediates alternative splicing of SRCI, without affecting pre-mRNA splicing generaity. Human Hub1 is highty similar to its yeast homotog, but its cellular function remains largely unexplored. Here, we show that human Hub1 binds to the spliceosomal protein Snu66 as in yeast; however, unlike its 5. cerevisioe homolos, human Hub1 is essential for viability. Prolonged in vivo depletion of human Hub1 leads to various cellular defects, including splicing speckle abnormalities, partial nuclear retention of mRNAs, mitotic catastrophe, and consequently cell death by apoptosis. Early consequences of Hub1 depletion are severe splicing defects, however, only for specific splice sites leading to exon skipping and intron retention. Thus, the ubiquitin-iike protein Hub1 is not a canonlcal spliceosomal factor needed generally for splicing, but rather a modulator of spliceosome performance and facilitator of alternative splicing.展开更多
文摘Seven different, but highly conserved 14-3-3 proteins are involved in diverse signaling pathways in human cells. It isunclear how the 14-3-3σ isoform, a transcriptional target of p53, exerts its inhibitory effect on the cell cycle in thepresence of other 14-3-3 isoforms, which are constitutively expressed at high levels. In order to identify structuraldifferences between the 14-3-3 isoforms, we solved the crystal structure of the human 14-3-3σ protein at a resolutionof 2.8 ? and compared it to the known structures of 14-3-3ζ and 14-3-3τ. The global architecture of the 14-3-3σ foldis similar to the previously determined structures of 14-3-3ζ and 14-3-3τ: two 14-3-3σ molecules form a cup-shapeddimer. Significant differences between these 14-3-3 isoforms were detected adjacent to the amphipathic groove, whichmediates the binding to phosphorylated consensus motifs in 14-3-3-ligands. Another specificity determining region islocalized between amino-acids 203 to 215. These differences presumably select for the interaction with specific ligands,which may explain the different biological functions of the respective 14-3-3 isoforms. Furthermore, the two 14-3-3σmolecules forming a dimer differ by the spatial position of the ninth helix, which is shifted to the inside of the ligandinteraction surface, thus indicating adaptability of this part of the molecule. In addition, 5 non-conserved residues arelocated at the interface between two 14-3-3σ proteins forming a dimer and represent candidate determinants of homo-and hetero-dimerization specificity. The structural differences among the 14-3-3 isoforms described here presumablycontribute to isoform-specific interactions and functions.
文摘Different from canonical ubiquitin-like proteins, Hub1 does not form covalent conjugates with substrates but binds proteins noncovalently. In Socchoromyces cerevisioe, Hub1 associates with spUceosomes and mediates alternative splicing of SRCI, without affecting pre-mRNA splicing generaity. Human Hub1 is highty similar to its yeast homotog, but its cellular function remains largely unexplored. Here, we show that human Hub1 binds to the spliceosomal protein Snu66 as in yeast; however, unlike its 5. cerevisioe homolos, human Hub1 is essential for viability. Prolonged in vivo depletion of human Hub1 leads to various cellular defects, including splicing speckle abnormalities, partial nuclear retention of mRNAs, mitotic catastrophe, and consequently cell death by apoptosis. Early consequences of Hub1 depletion are severe splicing defects, however, only for specific splice sites leading to exon skipping and intron retention. Thus, the ubiquitin-iike protein Hub1 is not a canonlcal spliceosomal factor needed generally for splicing, but rather a modulator of spliceosome performance and facilitator of alternative splicing.
