Effects of Combinatorial Expression of selA, selB and selC Genes on the Efficiency of Selenocysteine Incorporation in Escherichia coli

In Escherichia coil four gene products（selA, selB, selC and selD） and a selenocysteine（Sec） insertion sequence（SECIS） are required for the correct translation of UGA codons encoding Sec. Previous studies have shown that the stoichiometry of selenoproteine mRNA and elongation factor SelB affect the efficiency of Sec incorporation. Herein lies a detailed analysis of the effects of co-expressing selA, selB and selC genes under inducible promoters on the incorporation efficiency of Sec. Over-expression of either selA or selB reduced the efficiency of Sec incorporation by 61.1% or 11.6%, respectively, compared to the over-expression of the reporter vector alone did. Concomitant over-expression ofselC with selA or selB completely reversed the reduce of the efficiency of Sec but still reduced the efficiency of the incorporation relative to that observed for expression of selC alone. Over-expression of selC gene alone under L-arabinose induction reduced the efficiency of the incorporation relative to that observed for co-expressing selC with selA and selB under the control of its endogenous promoter in the absence of L-arabinose. Co-expression of selA, selB and selC with selA or selB under the control of inducible promoters increased the effi- ciency of Sec incorporation by 69.7%. Moreover, inducing selenoprotein-related gene expression during the late exponential phase increased the efficiency of Sec incorporation by a factor of 5.4 relative to that observed for the reporter vector alone. These results suggest that the co-expression of selA, selB and selC in Escherichia coli under the control of inducible promoters is a viable and promising strategy for increasing the yields of selenoproteins.

Animal secretory endolysosome channel discovery

Secretory pore-forming proteins(PFPs) have been identified in organisms from all kingdoms of life. Our studies with the toad species Bombina maxima found an interaction network among aerolysin family PFPs(af-PFPs) and trefoil factors(TFFs). As a toad af-PFP, Bm ALP1 can be reversibly regulated between active and inactive forms, with its paralog Bm ALP3 acting as a negative regulator. Bm ALP1 interacts with Bm TFF3 to form a cellular active complex called βγ-CAT. This PFP complex is characterized by acting on endocytic pathways and forming pores on endolysosomes, including stimulating cell macropinocytosis. In addition, cell exocytosis can be induced and/or modulated in the presence of βγ-CAT. Depending on cell contexts and surroundings, these effects can facilitate the toad in material uptake and vesicular transport, while maintaining mucosal barrier function as well as immune defense. Based on experimental evidence,we hereby propose a secretory endolysosome channel(SELC) pathway conducted by a secreted PFP in cell endocytic and exocytic systems, with βγ-CAT being the first example of a SELC protein. With essential roles in cell interactions and environmental adaptations, the proposed SELC protein pathway should be conserved in other living organisms.

氧化剂和香烟对血清抗弹性蛋白酶能力影响的体外观察

实验研究表明,氧化剂氯胺T、过氧化氢可抑制人血清抗弹性酶的能力。新鲜烟液可抑制人、犬、兔血清对弹性酶的抑制能力,人血清对烟液的敏感性大于犬和免。从而提示,吸烟是肺气肿的病因之一。