AB_(5)-type toxins are a group of secreted protein toxins that are central virulence factors for bacterial pathogens such as Shigella dysenteriae,Vibrio cholerae,Bordetella pertussis,and certain lineages of pathogenic...AB_(5)-type toxins are a group of secreted protein toxins that are central virulence factors for bacterial pathogens such as Shigella dysenteriae,Vibrio cholerae,Bordetella pertussis,and certain lineages of pathogenic Escherichia coli and Salmonella enterica.AB_(5) toxins are composed of an active(A)subunit that manipulates host cell biology in complex with a pentameric binding/delivery(B)subunit that mediates the toxin’s entry into host cells and its subsequent intracellular trafficking.Broadly speaking,all known AB_(5)-type toxins adopt similar structural architectures and employ similar mechanisms of binding,entering and trafficking within host cells.Despite this,there is a remarkable amount of diversity amongst AB_(5)-type toxins;this includes different toxin families with unrelated activities,as well as variation within families that can have profound functional consequences.In this review,we discuss the diversity that exists amongst characterized AB_(5)-type toxins,with an emphasis on the genetic and functional variability within AB_(5) toxin families,how this may have evolved,and its impact on human disease.展开更多
To understand the thermal evolution of lacustrine sedimentary n-alkane hydrogen isotopic composition(δD),especially bacterially derived n-alkanes,anhydrous thermal simulation experiments were performed with sediments...To understand the thermal evolution of lacustrine sedimentary n-alkane hydrogen isotopic composition(δD),especially bacterially derived n-alkanes,anhydrous thermal simulation experiments were performed with sediments from Lake Gahai(Gannan,China).We analyzed the original and pyrolysis-generated n-alkanes and theirδD values.The results showed that thermal maturity and n-alkane origins significantly affected the distribution of pyrolysis-generated n-alkanes.In immature to post-mature sediments,the bacterial-derived medium-chain n-alkanes generally had depletedδD values.The maximum difference in averageδD values between the bacterial-and herbaceous plant-derived medium-chain n-alkanes was 32‰,and the maximum difference in δD values among individual n-alkanes was 59‰.We found that the averageδD value of pyrolysis-generated n-alkanes from different latitude was significantly different in immature to highly mature sediments,but similar in post-mature ssediments.The hydrogen isotopes of sedimentary n-alkanes can be used as indicators for paleoclimate/paleo-environment conditions only when sediments are immature to highly mature.During thermal evolution,the δD value of generated individual n-alkanes and the averageδD value increased with thermal maturity,indicating that hydrogen isotopes of sedimentary n-alkanes can be used as an index of organic matter maturity.We established mathematical models of average δD values of generated n-alkanes from immature to post-mature sediments using n C_(21)^(-)/nC_(21)^(+)and average chain lengths.These results improve our understanding of the distribution andδD value of sedimentary n-alkanes derived from herbaceous plants in mid-latitude plateau cold regions.展开更多
DNA mismatch repair guards the integrity of the genome of almost all organisms by correcting DNA biosynthetic errors and by ensuring the fidelity of homologous genetic recombination. MutL is one of the important prote...DNA mismatch repair guards the integrity of the genome of almost all organisms by correcting DNA biosynthetic errors and by ensuring the fidelity of homologous genetic recombination. MutL is one of the important proteins involved in mismatch repair system. It has been suggested to function as a master coordinator or molecular matchmaker because it interacts physically with MutS, the endonuclease MutH, and DNA helicase UvrD. It also binds to DNA and has an ATPase activity. MutL defective bacteria strains have elevated mutation rates and it has been reported recently that MutL defect may have an important impact on bacterial evolution.展开更多
基金supported by a start-up grant provided by the Uni-versity of Alberta Faculty of Science(to C.C.F.)a Natural Sciences and Engineering Research Council of Canada(NSERC)Discovery Grant(Grant number:RGPIN-2020-03964 to C.C.F.).
文摘AB_(5)-type toxins are a group of secreted protein toxins that are central virulence factors for bacterial pathogens such as Shigella dysenteriae,Vibrio cholerae,Bordetella pertussis,and certain lineages of pathogenic Escherichia coli and Salmonella enterica.AB_(5) toxins are composed of an active(A)subunit that manipulates host cell biology in complex with a pentameric binding/delivery(B)subunit that mediates the toxin’s entry into host cells and its subsequent intracellular trafficking.Broadly speaking,all known AB_(5)-type toxins adopt similar structural architectures and employ similar mechanisms of binding,entering and trafficking within host cells.Despite this,there is a remarkable amount of diversity amongst AB_(5)-type toxins;this includes different toxin families with unrelated activities,as well as variation within families that can have profound functional consequences.In this review,we discuss the diversity that exists amongst characterized AB_(5)-type toxins,with an emphasis on the genetic and functional variability within AB_(5) toxin families,how this may have evolved,and its impact on human disease.
基金supported by the National Natural Science Foundation of China(Grant Nos.41772108 and 41972110)。
文摘To understand the thermal evolution of lacustrine sedimentary n-alkane hydrogen isotopic composition(δD),especially bacterially derived n-alkanes,anhydrous thermal simulation experiments were performed with sediments from Lake Gahai(Gannan,China).We analyzed the original and pyrolysis-generated n-alkanes and theirδD values.The results showed that thermal maturity and n-alkane origins significantly affected the distribution of pyrolysis-generated n-alkanes.In immature to post-mature sediments,the bacterial-derived medium-chain n-alkanes generally had depletedδD values.The maximum difference in averageδD values between the bacterial-and herbaceous plant-derived medium-chain n-alkanes was 32‰,and the maximum difference in δD values among individual n-alkanes was 59‰.We found that the averageδD value of pyrolysis-generated n-alkanes from different latitude was significantly different in immature to highly mature sediments,but similar in post-mature ssediments.The hydrogen isotopes of sedimentary n-alkanes can be used as indicators for paleoclimate/paleo-environment conditions only when sediments are immature to highly mature.During thermal evolution,the δD value of generated individual n-alkanes and the averageδD value increased with thermal maturity,indicating that hydrogen isotopes of sedimentary n-alkanes can be used as an index of organic matter maturity.We established mathematical models of average δD values of generated n-alkanes from immature to post-mature sediments using n C_(21)^(-)/nC_(21)^(+)and average chain lengths.These results improve our understanding of the distribution andδD value of sedimentary n-alkanes derived from herbaceous plants in mid-latitude plateau cold regions.
文摘DNA mismatch repair guards the integrity of the genome of almost all organisms by correcting DNA biosynthetic errors and by ensuring the fidelity of homologous genetic recombination. MutL is one of the important proteins involved in mismatch repair system. It has been suggested to function as a master coordinator or molecular matchmaker because it interacts physically with MutS, the endonuclease MutH, and DNA helicase UvrD. It also binds to DNA and has an ATPase activity. MutL defective bacteria strains have elevated mutation rates and it has been reported recently that MutL defect may have an important impact on bacterial evolution.
