Secretion of a bacterial cellulase by yeast

The secretion and post translational modification of interferons from Saccharomyces cerevisiae

Studies with three interferon molecules, IFN-alpha 2, IFN-beta 1, and a "hybrid" interferon, IFNX-430 are described which illustrate that both the expression and secretion characteristics of heterologous proteins in yeast cells reflect properties of the proteins themselves. Recombinant DNA techniques have also been used to demonstrate that the efficient processing of mature heterologous proteins from the yeast alpha factor secretion leader can be affected by sequences on the carboxyl side of the initial cleavage site. Secretion studies with heterologous proteins in S. cerevisiae are aimed at maximising yield, the percentage of extracellular product and correct amino terminus sequence. The results presented here show that all three factors are susceptible to currently unpredictable properties of the foreign sequence. This situation, in turn, means that heterologous proteins can be used as tools in the biochemical dissection of the yeast secretion process.

Expression of two Trichoderma reesei endoglucanases in the yeast Saccharomyces cerevisiae

The cDNA copies of the two endo-beta-1,4-glucanase genes, egl1 and egl3, from the filamentous fungus Trichoderma reesei were expressed in yeast Saccharomyces cerevisiae under the control of the yeast phosphoglycerate kinase gene promoter. Active EGI and EGIII enzyme was produced and secreted by yeast into the growth medium. The recombinant EGI enzyme was larger and more heterogeneous in size than the native enzyme secreted by Trichoderma, due to differences in the extent of N-glycosylation between these two organisms. The morphology of the yeast cells producing EGI or EGIII was clearly different from control strain.

In vivo evidence for posttranslational translocation and signal cleavage of the killer preprotoxin of Saccharomyces cerevisiae

A full-length cDNA of the M1 double-stranded RNA killer preprotoxin coding region successfully directed the synthesis of secreted K1 toxin when expressed in Saccharomyces cerevisiae from a plasmid vector. Three protein species immunoreactive with antitoxin antiserum were detected intracellularly in transformants harboring this killer cDNA plasmid. These toxin precursor species were characterized by using secretory-defective hosts, by comparative electrophoretic mobilities, and by tunicamycin susceptibility. Such studies indicate that these three protein species represent intermediates generated by signal cleavage of the preprotoxin and its subsequent glycosylation and provide evidence that these events occur posttranslationally.

In vivo evidence for posttranslational translocation and signal cleavage of the killer preprotoxin of Saccharomyces cerevisiae

A full-length cDNA of the M1 double-stranded RNA killer preprotoxin coding region successfully directed the synthesis of secreted K1 toxin when expressed in Saccharomyces cerevisiae from a plasmid vector. Three protein species immunoreactive with antitoxin antiserum were detected intracellularly in transformants harboring this killer cDNA plasmid. These toxin precursor species were characterized by using secretory-defective hosts, by comparative electrophoretic mobilities, and by tunicamycin susceptibility. Such studies indicate that these three protein species represent intermediates generated by signal cleavage of the preprotoxin and its subsequent glycosylation and provide evidence that these events occur posttranslationally.

Expression of cellulase genes in Rhodobacter capsulatus by use of plasmid expression vectors

Broad-host-range plasmid vectors were constructed for expression of heterologous genes in the photosynthetic bacterium Rhodobacter capsulatus. These plasmids utilize an RK2-derived replicon for maintenance and conjugative transfer and the R. capsulatus rxcA promoter to obtain transcription of genes within appropriately positioned DNA fragments. The expression vectors were used to obtain synthesis of endoglucanase and exoglucanase in R. capsulatus from cellulase genes present on exogenously derived DNA fragments. The cellulase genes were expressed either by use of their native translation initiation signals or by in-frame fusion with the rxcA B870 beta gene translation initiation signals to form a hybrid protein. The level of cellulase gene expression was found to be modulated in response to the extent of aeration of plasmid host cultures.

Analysis and utilization of the preprotoxin gene encoded in the M1 double-stranded RNA of yeast

The yeast type 1 toxin is a secreted protein which, along with immunity to the toxin, is encoded by an encapsidated double-stranded RNA (dsRNA) as a precursor protein, the preprotoxin. This chapter reviews recent work that has led to sequencing of complementary DNA (cDNA) copies of the preprotoxin gene, expression of toxin and toxin-immunity from cDNA, and use of the cDNA to effect secretion from yeast of a bacterial cellulase.

Characterization and structure of an endoglucanase gene cenA of Cellulomonas fimi

Two BamHI fragments (0.8 and 5.2 kb) of Cellulomonas fimi containing an endoglucanase (Eng) gene (cenA) were individually cloned into the BamHI site of pBR322; they expressed carboxymethylcellulase activity in Escherichia coli. The nucleotide (nt) sequence of the cenA gene was determined by sequencing overlapping deletions. The cenA gene is 1350 bp long encoding a polypeptide of 449 amino acids (aa) and stop codon. The 0.8-kb BamHI component encodes the first 76 aa, whereas the 5.2-kb BamHI component encodes the rest of the Eng. The Eng lacking the N-terminal 76 aa retains its activity and antigenicity, and it forms an active fusion protein with the N-terminal portion of the TcR determinant. The C-terminal region of the Eng is crucial for activity and a deletion of as little as 12 aa from that end results in the loss of all Eng activity. The N-terminal 31 aa of the Eng constitute a leader peptide which appears to be functional in exporting the enzyme to the periplasm in E. coli.