Manipulation and expression of the maize zein storage proteins in Escherichia coli

Clustering and cross-linking of the wheat storage protein α-gliadin: A combined experimental and theoretical approach

Our aim was to understand mechanisms for clustering and cross-linking of gliadins, a wheat seed storage protein type, monomeric in native state, but incorporated in network while processed. The mechanisms were studied utilizing spectroscopy and high-performance liquid chromatography on a gliadin-rich fraction, in vitro produced α-gliadins, and synthetic gliadin peptides, and by coarse-grained modelling, Monte Carlo simulations and prediction algorithms. In solution, gliadins with α-helix structures (dip at 205 nm in CD) were primarily present as monomeric molecules and clusters of gliadins (peaks at 650- and 700-s on SE-HPLC). At drying, large polymers (R_g 90.3 nm by DLS) were formed and β-sheets increased (14% by FTIR). Trained algorithms predicted aggregation areas at amino acids 115-140, 150-179, and 250-268, and induction of liquid-liquid phase separation at P- and Poly-Q-sequences (Score = 1). Simulations showed that gliadins formed polymers by tail-to-tail or a hydrophobic core (Kratky plots and R_ee = 35 and 60 for C- and N-terminal). Thus, the N-terminal formed clusters while the C-terminal formed aggregates by disulphide and lanthionine bonds, with favoured hydrophobic clustering of similar/exact peptide sections (synthetic peptide mixtures on SE-HPLC). Mechanisms of clustering and cross-linking of the gliadins presented here, contribute ability to tailor processing results, using these proteins.

RNA interference-mediated change in protein body morphology and seed opacity through loss of different zein proteins

Opaque or nonvitreous phenotypes relate to the seed architecture of maize (Zea mays) and are linked to loci that control the accumulation and proper deposition of storage proteins, called zeins, into specialized organelles in the endosperm, called protein bodies. However, in the absence of null mutants of each type of zein (i.e. alpha, beta, gamma, and delta), the molecular contribution of these proteins to seed architecture remains unclear. Here, a double null mutant for the delta-zeins, the 22-kD alpha-zein, the beta-zein, and the gamma-zein RNA interference (RNAi; designated as z1CRNAi, betaRNAi, and gammaRNAi, respectively) and their combinations have been examined. While the delta-zein double null mutant had negligible effects on protein body formation, the betaRNAi and gammaRNAi alone only cause slight changes. Substantial loss of the 22-kD alpha-zeins by z1CRNAi resulted in protein body budding structures, indicating that a sufficient amount of the 22-kD zeins is necessary for maintenance of a normal protein body shape. Among different mutant combinations, only the combined betaRNAi and gammaRNAi resulted in drastic morphological changes, while other combinations did not. Overexpression of alpha-kafirins, the homologues of the maize 22-kD alpha-zeins in sorghum (Sorghum bicolor), in the beta/gammaRNAi mutant failed to offset the morphological alterations, indicating that beta- and gamma-zeins have redundant and unique functions in the stabilization of protein bodies. Indeed, opacity of the beta/gammaRNAi mutant was caused by incomplete embedding of the starch granules rather than by reducing the vitreous zone.

Allelic variation and differential expression of methionine-rich delta-zeins in maize inbred lines B73 and W23a1

The sulfur-amino-acid-rich delta-zeins of maize ( Zea mays L.) are represented by 18-kDa and 10-kDa proteins. We have cloned a novel 11-kDa methionine-rich delta-zein from developing endosperm of the inbred line W23a1. The nucleotide sequence of this new delta-zein is identical to the published 10-kDa delta-zein, except for an insertion of 18 nucleotides between +316 and +333 bp from the translation start site. Antibodies raised against the recombinant 18-kDa delta-zein recognized both the 18-kDa and 10-kDa delta-zein from total seed protein extracts of different maize inbred lines. Western blot analysis revealed differences in the levels of the delta-zeins in different inbred lines and some of the inbred lines lacked either the 10-kDa or the 18-kDa delta-zeins. Northern blot analysis revealed temporal differences in the RNA transcript levels of the 11-kDa and 18-kDa delta-zeins between B73 and W23a1. Such differences were not evident on Western blot analysis where similar protein accumulation profiles were seen for both lines. Immunostaining of paraffin sections of developing maize endosperm with the 18-kDa delta-zein antibodies revealed specific labeling of protein bodies found in the first few starchy layers from the aleurone layer. Electron-microscopic observation of thin-sections of B73 and W23a1 endosperm cells confirmed the presence of recently discovered novel, vacuole-like structures in these inbred lines. Immunogold labeling studies revealed that the delta-zeins were localized in the endoplasmic-reticulum-derived protein bodies and showed no preferential gold particle labeling over either the light or electron-dense material found in these protein bodies.

Extended nucleocapsid protein is cleaved from the Gag-Pol precursor of human immunodeficiency virus type 1

Human immunodeficiency virus type 1 Gag and Gag-Pol precursors are translated from an mRNA which is indistinguishable from the full-length genomic RNA. The ratio of Gag to Gag-Pol polyproteins is approximately 20:1 and is controlled by a frameshift of the reading frame, which takes place downstream of the p7 nucleocapsid (NC) in the N terminus of the p1 peptide. The viral precursors Gag and Gag-Pol are cleaved by the virus-encoded protease (PR) into the structural proteins, and into p6(Pol), PR, reverse transcriptase and integrase. Due to the frameshift event, the cleavage site at the C terminus of NC coded in the Gag frame (ERQAN-FLGKI) changes either to ERQANFLRED or ERQANFFRED. The results presented in this report demonstrate that the NC released from the Gag-Pol precursor is 8 amino acid residues longer than the NC cleaved from the Gag polyprotein. Our results also show that truncated Gag-Pol precursors bearing cleavage site mutation at the NC/p6(Pol), and/or p6(Pol)/PR junctions, undergo autoprocessing in bacterial and eukaryotic cells, indicating that PR is active when part of the precursor.

Human immunodeficiency virus type 1 gag-protease fusion proteins are enzymatically active

We have introduced mutations into the region of the genome of human immunodeficiency virus type 1 (HIV-1) that encodes the cleavage sites between the viral protease (PR) and the adjacent upstream region of the polyprotein precursor. Segments containing these mutations were introduced into plasmids, and the retroviral proteins were expressed in Escherichia coli. The mutations prevented cleavage between the PR and the adjacent polypeptide; however, other PR cleavage sites in the polyprotein were cleaved normally, showing that the release of free PR is not a prerequisite for the appropriate processing of HIV-1 precursors.

Mutational analysis of the DNA polymerase and ribonuclease H activities of human immunodeficiency virus type 2 reverse transcriptase expressed in Escherichia coli

We have constructed a plasmid that, when introduced into Escherichia coli, induces the synthesis of large quantities of a polypeptide with an apparent molecular weight of 68 kDa. The HIV-2 reverse transcriptase (RT) made in E. coli is soluble in bacterial extracts and possesses both RNA-dependent DNA polymerase and ribonuclease H (RNase H) activities typical of retroviral RTs. The HIV-2 RT expression clone was used to generate mutations in HIV-2 RT. There is a strong correlation between the effects of individual mutations on the DNA polymerase and RNase H activities. Mutations that profoundly affect the two catalytic functions are not clustered in any particular region of the polypeptide. Those few mutations that selectively affect either the RNase H or the DNA polymerase suggest that, like other retroviral RTs, the DNA polymerase is associated with the amino-terminal portion of HIV-2 RT and the RNase H with the carboxy-terminal portion. Genetically, the HIV-2 RT resembles the HIV-1 RT more closely than it resembles Moloney murine leukemia virus RT. The two catalytic functions of Moloney murine leukemia virus RT can be separately expressed in active form by molecular cloning; those of HIV-1 and HIV-2 RT cannot.

Superpolylinkers in cloning and expression vectors

Versatile DNA polylinkers of more than 300 bp were constructed. They contain the recognition sequences of all restriction enzymes--whether known or still to be discovered--that recognize palindromic hexamers. In addition to these 64 uninterrupted hexameric recognition sites, a number of sites containing interrupted palindromes and nonpalindromic sequences and two recognition sequences with 8 bp are present. Polylinkers (in several variants) were inserted into frequently utilized Escherichia coli cloning vectors such as pBluescript (yielding pSLJ10, pSL250, pSL260, pSL270, and pSL300), pUC18/pUC19 (yielding pSL180 and pSL190, respectively), or pUC118/pUC119 (yielding pSL1180 and pSL1190, respectively). A subtle color discrimination between presence and absence of insert in pSL300 (mid-blue to light-blue or white) was seen in a number of test ligations. The mid-blue color that is generated by pSL300 is presumably due to translational restarts. A different intergenic region for translational restarts was used in plasmids pSL251, pSL261, pSL271, and pSL301. The polylinker was also inserted into expression vector pUC120, yielding pSE1200, and into expression vector pKK233-2, yielding pSE220 and a shortened version thereof, pSE280. Finally, the polylinker was inserted into pTrc99A, resulting in pSE380, which carries a lac repressor gene. This expands the use of the expression system beyond lacIq strains to other bacterial hosts. These versatile vectors have broad applications in genetic engineering.

Expression in Escherichia coli of a Moloney murine leukemia virus reverse transcriptase whose structure closely resembles the viral enzyme

We have constructed an expression plasmid containing the portion of the Moloney murine leukemia virus genome encoding the reverse transcriptase (RT). When introduced into Escherichia coli this plasmid induces the synthesis of a 70-kDa protein. The RT made in E. coli differs from the viral protein only in that there are two new amino acids, methionine and glycine, substituted for the threonine found at the N terminus of the viral enzyme. Approximately half of the E. coli synthesized RT enzyme is soluble in cell extracts. This protein is active in an RT assay, and like the enzyme purified from virions, is more active in the presence of Mn2+ than Mg2+. We have also constructed a plasmid that induces the synthesis of an RT-integration protein fusion.