Biomedical subjects

J E Mott

Publications and source records attributed to J E Mott.

10 recordsLinked to original sources

PubMed2002

A spontaneous runaway vector for production-scale expression of bovine somatotropin from Escherichia coi.

An Escherichia coli expression vector was constructed for the production-scale fermentation of recombinant bovine somatotropin (rBST). Gene expression is regulated by a spontaneous increase in copy number at a constant low temperature without the need for an external inducer. This vector, designated pURA-4, contains the ampicillin resistance gene, the replication origin from pBR322, the R1 temperature-inducible runaway replicon, and a gene encoding rBST. Optimized rBST expression levels of >35% total cell protein were achieved at a constant 28 degrees C. Shake-flask analysis of pURA-4 shows that the copy number spontaneously increases approximately 6-fold during rBST production. Investigation into the mechanism of pURA-4 spontaneous runaway shows that the increase in copy number is directed by the pBR322 ori and not by the R1 replicon. Although the R1 temperature-inducible replicon does not mediate spontaneous runaway, it does have a positive effect on rBST expression. Copy number analysis also confirmed the stability of pURA-4 spontaneous runaway from the shake-flask scale through the production scale.

Animals↗

PubMed2000

Modification of the carboxy-terminal amino acid sequence alters the Escherichia coli expression of a gene encoding multiple repeats of a bovine growth hormone releasing factor analog.

Since investigations into the determinants of intracellular protein degradation have shown that the carboxy terminal sequence can be a critical factor for protein expression in Escherichia coli, we attempted to increase the expression of a protein containing multiple repeats of a bovine growth hormone releasing factor analog (bGRF30) by modifying the carboxy terminus with the addition of short amino acid extensions derived from stable E. coli proteins. Extensions capable of increasing bGRF30 per liter titers up to four-fold, as well as extensions that completely abolished bGRF30 expression were identified. Select C-terminal extensions were investigated further to determine the mechanism by which they affected bGRF30 expression. Analysis of mRNA levels and protein production titers suggests that extensions which increase bGRF30 titers primarily affect protein stability and ribosomal release. Negative extensions exert their influence through a more complex mechanism, appearing to interfere with the ability of ribosomes to be efficiently released from their cognate mRNA.

Amino Acid Sequence↗

PubMed1998

Cation binding to the integrin CD11b I domain and activation model assessment.

BACKGROUND: The integrin family of cell-surface receptors mediate cell adhesion through interactions with the extracellular matrix or other cell-surface receptors. The alpha chain of some integrin heterodimers includes an inserted 'I domain' of about 200 amino acids which binds divalent metal ions and is essential for integrin function. Lee et al. proposed that the I domain of the integrin CD11b adopts a unique 'active' conformation when bound to its counter receptor. In addition, they proposed that the lack of adhesion in the presence of Ca2+ ion reflected the stabilization of an 'inactive' I-domain conformation. We set out to independently determine the structure of the CD11 b I domain and to evaluate the structural effects of divalent ion binding to this protein. RESULTS: We have determined the X-ray structure of a new crystal form of the CD11 b I domain in the absence of added metal ions by multiple isomorphous replacement (MIR). Metal ions were easily introduced into this crystal form allowing the straight-forward assessment of the structural effects of divalent cation binding at the metal ion dependent adhesion site (MIDAS). The equilibrium binding constants for these ions were determined by titration calorimetry. The overall protein conformation and metal-ion coordination of the I domain is the same as that observed for all previously reported CD11 a I-domain structures and a CD11 b I-domain complex with Mn2+. These structures define a majority conformation. CONCLUSIONS: Addition of the cations Mg2+, Mn2+ and Cd2+ to the metal-free I domain does not induce conformational changes in the crystalline environment. Moreover, we find that Ca2+ binds poorly to the I domain which serves to explain its failure to support adhesion. We show that the active conformation proposed by Lee et al, is likely to be a construct artifact and we propose that the currently available data do not support a dramatic structural transition for the I domain during counter-receptor binding.

Amino Acid Sequence↗

PubMed1998

Structural characterizations of nonpeptidic thiadiazole inhibitors of matrix metalloproteinases reveal the basis for stromelysin selectivity.

The binding of two 5-substituted-1,3,4-thiadiazole-2-thione inhibitors to the matrix metalloproteinase stromelysin (MMP-3) have been characterized by protein crystallography. Both inhibitors coordinate to the catalytic zinc cation via an exocyclic sulfur and lay in an unusual position across the unprimed (P1-P3) side of the proteinase active site. Nitrogen atoms in the thiadiazole moiety make specific hydrogen bond interactions with enzyme structural elements that are conserved across all enzymes in the matrix metalloproteinase class. Strong hydrophobic interactions between the inhibitors and the side chain of tyrosine-155 appear to be responsible for the very high selectivity of these inhibitors for stromelysin. In these enzyme/inhibitor complexes, the S1' enzyme subsite is unoccupied. A conformational rearrangement of the catalytic domain occurs that reveals an inherent flexibility of the substrate binding region leading to speculation about a possible mechanism for modulation of stromelysin activity and selectivity.

Animals↗

PubMed1997

Use of the HIV-1 protease for excision of growth-hormone-releasing factor from synthetic and recombinant peptide precursors.

An autolysis-resistant mutant of the HIV-I protease was employed for removal of metabolically stabilized and highly bioactive analogues of bovine growth-hormone-releasing factor (bGRF) from their larger either synthetic or recombinant precursors. The N-terminal four amino acids in two selected model GRF analogues, Y1IDAIFTSSYRKVLAQLSARKLLQDILSRQVF32-OH (I; GRF32) and Y1IDAIFTSSYRKVLAQLSARKLLQDILSRQ30-OH (IA; GRF30), conform well to the specificity of the HIV-I protease for residues in the P1' to P4' positions of its peptide substrates. A variety of amino acids were tried in the N-terminal extension (positions P4-P1) to fit the protease substrate specificity for the 8 amino acids in positions P4-P4'. A synthetic precursor of I, extended N-terminally with RQVF-, a sequence representing the four C-terminal residues in I, was effectively cleaved by the protease at the Phe-1-Tyr1 bond (... RQVF-decreases-YIDA ...) to release GRF32. However, when several soluble fusion proteins linked to GRF32 by the RQVF sequence were expressed in Escherichia coli, attempts to cleave out the core GRF32 met with variable, and only limited, success. By random mutagenesis in a propeptide segment, [MGQSVAQVF]-decreases-GRF30, (II) was identified as a construct that showed reasonably high-level expression in E. coli and was effectively processed by the HIV-I protease. A yield of 5 mg of pure GRF30 was obtained/litre of culture medium after a single HPLC purification step.

Amino Acid Sequence↗

PubMed1993

Biochemical diversity in a phage display library of random decapeptides.

Detailed knowledge and understanding of the structure and function of biologically important macromolecules is frequently insufficient to permit rational, de novo design of recognition molecules and therapeutics. Traditional drug discovery has, thus, focused on screening and identifying native molecules as drugs or as templates for genetic engineering or organic synthesis. The number and novelty of lead compounds for drug discovery might be expanded significantly, however, by the ability to express and screen large libraries of peptide structures with phage display technologies [Scott and Smith, Science 249 (1990) 386-390]. The significance of such libraries as sources of novel biological ligands will depend in part on the depth and degree of biochemical diversity they comprise. We have prepared a phage display library of greater than 2 x 10(6) individual decapeptides produced as N-terminal fusions to the pIII surface protein of fd filamentous phage. The decapeptides were expressed from a degenerate DNA insert sequence that was chemically synthesized with an equal mixture of all four nucleotide bases at the three positions in each of the ten codons. Fifty-two clones were picked randomly and without prior selection from the population and the sequences of their peptide inserts were determined. Our results confirm and document the broad representation at the primary amino acid sequence level that is expected in a library expressed from random DNA inserts. More significantly, biochemical characterization shows these insert sequences correspond to structures comprising a wide range and combination of isoelectric, hydropathic, and biochemical properties necessary in drug discovery to access a significant percentage of the repertoire of possible peptide structures by affinity or activity screening.

Amino Acid Sequence↗

PubMed1993

Absence of persistence and transfer of genetic material by recombinant Escherichia coli in conventional, antibiotic-treated mice.

Strain BST-1 is a derivative of Escherichia coli K-12 that carries a plasmid designated pURA-4 and is the expression system used by The Upjohn Company in the production of recombinant bovine somatotropin (rbSt). This plasmid also encodes an ampicillin resistance gene. The plasmidless carrier strain, BST-1C, contains a gene for tetracycline resistance which is provided by the chromosomal insertion of the transposon Tn10. Therefore, BST-1 is resistant to ampicillin and tetracycline, while BST-1C is resistant only to tetracycline. The Food and Drug Administration requested that we conduct an environmental assessment study to monitor the 'persistence of the recombinant live K-12 E. coli organism compared to the host E. coli organism'. In addition, we were requested to monitor 'the potential transfer of genetic material from (our) recombinant organism to the indigenous microflora' of the mouse gastrointestinal (GI) tract. The differences in persistence were determined by monitoring shedding of BST-1 and BST-1C in the feces of conventionally reared, outbred mice inoculated with either of the two strains. Even with antibiotic selective pressure applied (tetracycline in the water), BST-1 did not persist as well as the non-plasmid carrying parental stain, BST-1C. In the gene transfer experiments, transfer of pURA-4 was monitored by the appearance of the ampicillin resistance marker and/or by hybridization assays for the rbSt gene in indigenous, mouse-colonizing E. coli strains which had been made streptomycin resistant. At the limit of detection, no transfer of pURA-4 was detected either in vitro or in vivo. These data support an interpretation that BST-1 does not present an environmental hazard as measured by colonization/persistence in the gut of conventionally reared mammals.

Ampicillin Resistance↗

PubMed1985

Maturation of Escherichia coli tryptophan operon mRNA: evidence for 3' exonucleolytic processing after rho-dependent termination.

The mature 3' end of Escherichia coli tryptophan operon mRNA in vivo coincides with a site (trp t) having features commonly associated with rho-independent terminators in bacteria. Efficient generation of this 3' end in vivo is nevertheless affected by a distal rho-dependent site (trP-t'), though these two sites behave independently in vitro. We have cloned these sites upstream of the galactokinase gene (galK), and galactokinase levels in vivo indicate that, as terminators per se, their efficiencies (37% for trp t, and 79% for trp t') do not differ significantly from those observed in vitro. However, when the trp t hairpin is placed between galK and a downstream copy of trp t', galactokinase levels are enhanced 2- to 3-fold. This suggests the involvement of a post-transcriptional event, such as RNA processing, in determining the level of gene activity. Indeed, in the presence of the 3' exonuclease RNase II, mRNA terminated by rho factor in vitro at the trp t' site is processed back to the trp t site. The remote trp t' region appears to be the major termination site for trp mRNA, and the trp t hairpin serves a dual function-as a minor terminator, and as a protective barrier to 3' exonucleolytic degradation. We infer that the tandem terminators, rho factor, and RNA processing are all required to generate the mature 3' end of this bacterial mRNA.

Base Sequence↗

PubMed1985

Maximizing gene expression from plasmid vectors containing the lambda PL promoter: strategies for overproducing transcription termination factor rho.

We have constructed two plasmids in which transcription of the rho gene from Escherichia coli K-12 is under the control of the lambda phage PL promoter. In p31-356, the normal rho promoter is deleted, but the remainder of the rho leader region, including the ribosome binding site, is present. In p39-AS, the rho leader is completely absent, and the lambda cII ribosome binding site replaces that of rho. Under noninducing conditions, expression of rho protein from these plasmids is repressed by the lambda cI protein in hosts carrying lambda cryptic prophage. Induction using mitomycin C or nalidixic acid in a cryptic lysogen carrying the cI+ repressor resulted in the overproduction of rho protein to levels of 3%-5% of the total cellular protein with p31-356, and to levels of approximately equal to 40% with p39-AS. The overproduced protein is functionally indistinguishable from the rho protein isolated from the K-12 strain W3110, and it can be obtained from cells harboring p39-AS in yields of up to 25 mg of rho per g of cells. In contrast to chemical induction, heat induction in four cryptic lambda lysogens carrying the thermolabile cI857 repressor failed to yield the same high levels of rho protein (with either plasmid). Our results show that chemical induction of PL-containing plasmid expression vectors can serve as a convenient and useful alternative to the commonly used method of heat induction.

Bacteriophage lambda↗

PubMed1984

Targeted mutagenesis in vitro: lac repressor mutations generated using AMV reverse transcriptase and dBrUTP.

We have cloned the gene for the lac operon repressor (lacI) of Escherichia coli into the M13 related phage f1. Mutagenesis of the lacI gene was performed in vitro by filling dsDNA molecules gapped over the lacI gene with Avian Myeloblastosis Virus (AMV) reverse transcriptase. LacI mutants are found at a frequency of 1 in 10(4) using a genetic screen in vivo. For two-thirds of the 60 mutants, lesions were identified within the first 400 bases of lacI, by dideoxy sequencing. An unexpectedly wide range of different lesions were observed, including transitions, transversions, and deletions (of which the most common were the removal of single base pairs). The replacement of dTTP by dBrUTP in the filling reaction resulted in a doubling of deletions in the sample population as well as the anticipated T to C and C to T transitions. Although the lacI gene has been extensively studied in vivo, the power of this technique for mutagenesis in vitro is demonstrated by the generation of three previously undescribed lacI mutations.

Amino Acid Sequence↗