Mitogen-activated protein kinase(MAPK) cascades play pivotal roles in plant defense against phytopathogens downstream of immune receptor complexes. The amplitude and duration of MAPK activation must be strictly contro...Mitogen-activated protein kinase(MAPK) cascades play pivotal roles in plant defense against phytopathogens downstream of immune receptor complexes. The amplitude and duration of MAPK activation must be strictly controlled, but the underlying mechanism remains unclear. Here, we identified Arabidopsis CPL1(C-terminal domain phosphatase-like 1)as a negative regulator of microbe-associated molecular pattern(MAMP)-triggered immunity via a forward-genetic screen. Disruption of CPL1 significantly enhanced plant resistance to Pseudomonas pathogens induced by the bacterial peptide fg22. Furthermore, fg22-induced MPK3/MPK4/MPK6 phosphorylation was dramatically elevated in cpl1 mutants but severely impaired in CPL1 overexpression lines, suggesting that CPL1 might interfere with fg22-induced MAPK activation. Indeed, CPL1 directly interacted with MPK3 and MPK6, as well as the upstream MKK4 and MKK5. A firefy luciferase-based complementation assay indicated that the interaction between MKK4/MKK5 and MPK3/MPK6 was significantly reduced in the presence of CPL1. These results suggest that CPL1 plays a novel regulatory role in suppressing MAMP-induced MAPK cascade activation and MAMP-triggered immunity to bacterial pathogens.展开更多
Human maltase-glucoamylase(MGAM)hydrolyzes linear alpha-1,4-linked oligosaccharide substrates,playing a crucial role in the production of glucose in the human lumen and acting as an efficient drug target for type 2 di...Human maltase-glucoamylase(MGAM)hydrolyzes linear alpha-1,4-linked oligosaccharide substrates,playing a crucial role in the production of glucose in the human lumen and acting as an efficient drug target for type 2 diabetes and obesity.The amino-and carboxyl-terminal portions of MGAM(MGAM-N and MGAM-C)carry out the same catalytic reaction but have different substrate specificities.In this study,we report crystal structures of MGAM-C alone at a resolution of 3.1Å,and in complex with its inhibitor acarbose at a resolution of 2.9Å.Structural studies,combined with biochemical analysis,revealed that a segment of 21 amino acids in the active site of MGAM-C forms additional sugar subsites(+2 and+3 subsites),accounting for the preference for longer substrates of MAGM-C compared with that of MGAM-N.Moreover,we discovered that a single mutation of Trp1251 to tyrosine in MGAM-C imparts a novel catalytic ability to digest branched alpha-1,6-linked oligosaccharides.These results provide important information for understanding the substrate specificity of alphaglucosidases during the process of terminal starch digestion,and for designing more efficient drugs to control type 2 diabetes or obesity.展开更多
Plants possess both types of endosymbiotic organelles, chloroplasts and mitochondria. Transit peptides and presequences function as signal sequences for specific import into chloroplasts and mitochondria, respectively...Plants possess both types of endosymbiotic organelles, chloroplasts and mitochondria. Transit peptides and presequences function as signal sequences for specific import into chloroplasts and mitochondria, respectively. However, how these highly similar signal sequences confer the protein import specificity remains elusive. Here, we show that mitochondrial- or chloroplast-specific import involves two distinct steps, specificity determination and translocation across envelopes, which are mediated by the N-terminal regions and functionally interchangeable C-terminal regions, respectively, of transit peptides and presequences. A domain harboring multiple-arginine and hydrophobic sequence motifs in the N-terminal regions of presequences was identified as the mitochondrial specificity factor. The presence of this domain and the absence of arginine residues in the N-terminal regions of otherwise common targeting signals confers specificity of protein import into mitochondria and chloroplasts, respectively. AtToc159, a chloroplast import receptor, also contributes to determining chloroplast import specificity. We propose that common ancestral sequences were functionalized into mitochondrial- and chloroplast-specific signal sequences by the presence and absence, respectively, of multiple-arginine and hydrophobic sequence motifs in the N-terminal region.展开更多
基金supported by the National Natural Science Foundation of China (grant no. 31671991 to FC)。
文摘Mitogen-activated protein kinase(MAPK) cascades play pivotal roles in plant defense against phytopathogens downstream of immune receptor complexes. The amplitude and duration of MAPK activation must be strictly controlled, but the underlying mechanism remains unclear. Here, we identified Arabidopsis CPL1(C-terminal domain phosphatase-like 1)as a negative regulator of microbe-associated molecular pattern(MAMP)-triggered immunity via a forward-genetic screen. Disruption of CPL1 significantly enhanced plant resistance to Pseudomonas pathogens induced by the bacterial peptide fg22. Furthermore, fg22-induced MPK3/MPK4/MPK6 phosphorylation was dramatically elevated in cpl1 mutants but severely impaired in CPL1 overexpression lines, suggesting that CPL1 might interfere with fg22-induced MAPK activation. Indeed, CPL1 directly interacted with MPK3 and MPK6, as well as the upstream MKK4 and MKK5. A firefy luciferase-based complementation assay indicated that the interaction between MKK4/MKK5 and MPK3/MPK6 was significantly reduced in the presence of CPL1. These results suggest that CPL1 plays a novel regulatory role in suppressing MAMP-induced MAPK cascade activation and MAMP-triggered immunity to bacterial pathogens.
基金by the National Basic Research Program of China(973 Program)(Grant Nos.2007CB914301 and 2007CB 914803)the Natural Science Foundation of China(Grant Nos.30940015,30770428,21002052 and 31170684)the TBR Program(No.08QTPTJC 28200,08SYSYTC00200 and 10JCYB JC14300).
文摘Human maltase-glucoamylase(MGAM)hydrolyzes linear alpha-1,4-linked oligosaccharide substrates,playing a crucial role in the production of glucose in the human lumen and acting as an efficient drug target for type 2 diabetes and obesity.The amino-and carboxyl-terminal portions of MGAM(MGAM-N and MGAM-C)carry out the same catalytic reaction but have different substrate specificities.In this study,we report crystal structures of MGAM-C alone at a resolution of 3.1Å,and in complex with its inhibitor acarbose at a resolution of 2.9Å.Structural studies,combined with biochemical analysis,revealed that a segment of 21 amino acids in the active site of MGAM-C forms additional sugar subsites(+2 and+3 subsites),accounting for the preference for longer substrates of MAGM-C compared with that of MGAM-N.Moreover,we discovered that a single mutation of Trp1251 to tyrosine in MGAM-C imparts a novel catalytic ability to digest branched alpha-1,6-linked oligosaccharides.These results provide important information for understanding the substrate specificity of alphaglucosidases during the process of terminal starch digestion,and for designing more efficient drugs to control type 2 diabetes or obesity.
文摘Plants possess both types of endosymbiotic organelles, chloroplasts and mitochondria. Transit peptides and presequences function as signal sequences for specific import into chloroplasts and mitochondria, respectively. However, how these highly similar signal sequences confer the protein import specificity remains elusive. Here, we show that mitochondrial- or chloroplast-specific import involves two distinct steps, specificity determination and translocation across envelopes, which are mediated by the N-terminal regions and functionally interchangeable C-terminal regions, respectively, of transit peptides and presequences. A domain harboring multiple-arginine and hydrophobic sequence motifs in the N-terminal regions of presequences was identified as the mitochondrial specificity factor. The presence of this domain and the absence of arginine residues in the N-terminal regions of otherwise common targeting signals confers specificity of protein import into mitochondria and chloroplasts, respectively. AtToc159, a chloroplast import receptor, also contributes to determining chloroplast import specificity. We propose that common ancestral sequences were functionalized into mitochondrial- and chloroplast-specific signal sequences by the presence and absence, respectively, of multiple-arginine and hydrophobic sequence motifs in the N-terminal region.
