Construction and stability of a sixfold repeated artificial gene

Expression of acid cleavable Asp-Pro linked multimeric AFP peptide in E. coli

Background

Difficult to express peptides are usually produced by co-expression with fusion partners. In this case, a significant mass part of the recombinant product falls on the subsequently removed fusion partner. On the other hand, multimerization of peptides is known to improve its proteolytic stability in E. coli due to the inclusion of body formation, which is sequence specific. Thereby, the peptide itself may serve as a fusion partner and one may produce more than one mole of the desired product per mole of fusion protein. This paper proposes a method for multimeric production of a human alpha-fetoprotein fragment with optimized multimer design and processing. This fragment may further find its application in the cytotoxic drug delivery field or as an inhibitor of endogenous alpha-fetoprotein.

Results

Multimerization of the extended alpha-fetoprotein receptor-binding peptide improved its stability in E. coli, and pentamer was found to be the largest stable with the highest expression level. As high as 10 aspartate-proline bonds used to separate peptide repeats were easily hydrolyzed in optimized formic acid-based conditions with 100% multimer conversion. The major product was represented by unaltered functional alpha-fetoprotein fragment while most side-products were its formyl-Pro, formyl-Tyr, and formyl-Lys derivatives. Single-step semi-preparative RP-HPLC was enough to separate unaltered peptide from the hydrolysis mixture.

Conclusions

A recombinant peptide derived from human alpha-fetoprotein can be produced via multimerization with subsequent formic acid hydrolysis and RP-HPLC purification. The reported procedure is characterized by the lower reagent cost in comparison with enzymatic hydrolysis of peptide fusions and solid-phase synthesis. This method may be adopted for different peptide expression, especially with low amino and hydroxy side chain content.

Supplementary Information

The online version contains supplementary material available at 10.1186/s43141-021-00265-5.

Preparation of multimilligram quantities of large, linear DNA molecules for structural studies

We describe a method for preparing large, linear DNA molecules in amounts that are suitable for structural studies. The procedure employs self-primed DNA amplification on a starting molecule that consists of the sequence of interest flanked by the cohesive end sequences from bacteriophage lambda as well as endonuclease recognition sites. Amplification produces long polymers of DNA, tens of kilobases in length, which harbor many copies of the sequence of interest. Endonuclease digestion of these polymers, followed by chromatographic purification, yields high-quality preparations of the DNA molecule of interest. Reliance on the cohesive end sequences to initiate self-primed amplification effectively enables the synthesis of DNA molecules of interest with minimal restriction on length and sequence.

Formation of de novo centromeres and construction of first-generation human artificial microchromosomes

We have combined long synthetic arrays of alpha satellite DNA with telomeric DNA and genomic DNA to generate artificial chromosomes in human HT1080 cells. The resulting linear microchromosomes contain exogenous alpha satellite DNA, are mitotically and cytogenetically stable in the absence of selection for up to six months in culture, bind centromere proteins specific for active centromeres, and are estimated to be 6-10 megabases in size, approximately one-fifth to one-tenth the size of endogenous human chromosomes. We conclude that this strategy results in the formation of de novo centromere activity and that the microchromosomes so generated contain all of the sequence elements required for stable mitotic chromosome segregation and maintenance. This first-generation system for the construction of human artificial chromosomes should be suitable for dissecting the sequence requirements of human centromeres, as well as developing constructs useful for therapeutic applications.

Genetic analysis of a Pseudomonas locus encoding a pathway for biphenyl/polychlorinated biphenyl degradation

The cistronic organization of the bph locus, encoding a biphenyl/polychlorinated biphenyl (PCB) degradation pathway in Pseudomonas sp. LB400, has been elucidated. Seven structural genes, encoding biphenyl dioxygenase (bphA1A2A3A4), biphenyl-2,3-dihydrodiol-2,3-dehydrogenase (bphB), biphenyl-2,3-diol-1,2-dioxygenase (bphC) and 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoate hydrolase (bphD), have been located. The complete sequences of bphB, bphC and bphD are reported. Taken together with the data of Erickson and Mondello [J. Bacteriol. 174 (1992) 2903-2912], Pseudomonas sp. LB400 is now the first strain for which the sequences of all genes encoding the catabolism from biphenyls to benzoates have been determined. Comparisons of the deduced amino acid (aa) sequences of BphB, BphC and BphD with those of related proteins led to predictions about catalytically important aa residues. Six Bph have been detected and identified. Five of them could be obtained as the most abundant proteins when their genes were expressed in Escherichia coli.

A high efficiency method for site-directed mutagenesis with any plasmid

A procedure is described which allows for the site-directed mutagenesis of DNA segments in any double-stranded plasmid with high efficiency. There are no limitations as to the position of the mutation. The protocol involves only simple enzymatic manipulations and no difficult to control operations, such as partial digestions, are required. The method was developed and used to mutagenize two different genes (encoding human interferon-beta and interleukin-2) cloned in a eukaryotic expression vector. For ten mutageneses with different oligodeoxyribonucleotides the average yield of mutants was 60%.