Biomedical subjects

M Mikolajczak

Publications and source records attributed to M Mikolajczak.

4 recordsLinked to original sources

PubMed1997

Production of xanthan gum by Sphingomonas bacteria carrying genes from Xanthomonas campestris.

Twelve genes coding for assembly, acetylation, pyruvylation, polymerization, and secretion of the polysaccharide xanthan gum are clustered together on the chromosome of the bacterium Xanthomonas campestris. These genes (gumBCDEFGHIJKLM) are sufficient for synthesis of xanthan gum when placed in bacteria from a different genus, Sphingomonas. The polysaccharide from the recombinant microorganism is largely indistinguishable, structurally and functionally, from native xanthan gum. These results demonstrate that a complex pathway for biosynthesis of a specific polysaccharide can be acquired by a single inter-generic transfer of genes between bacteria. This suggests the biological and commercial feasibility of synthesizing xanthan gum or other polysaccharides in non-native hosts.

DNA, Recombinant↗

PubMed1996

Linkage of genes essential for synthesis of a polysaccharide capsule in Sphingomonas strain S88.

Several structurally related capsular polysaccharides that are secreted by members of the genus Sphingomonas are being developed as aqueous rheological control agents for diverse industrial and food applications. They include gellan (S-60), welan (S-130), rhamsan (S-194), S-657, S-88, S-198, S-7, and NW-11. We refer to these polysaccharides as sphingans, after the genus name. This paper characterizes the first gene cluster isolated from a Sphingomonas species (S88) that is required for capsule synthesis. Overlapping DNA segments which spanned about 50 kbp of S88 DNA restored the synthesis of sphingan S-88 in capsule-negative mutants. The mutations were mapped into functional complementation groups, and the contiguous nucleotide sequence for the 29-kbp cluster was determined. The genetic complementation map and the DNA sequences were interpreted as an extended multicistronic locus containing genes essential for the assembly and secretion of polysaccharide S-88. Many of the deduced amino acid sequences were similar to gene products from other polysaccharide-secreting bacteria such as Rhizobium meliloti (succinoglycan), Xanthomonas campestris (xanthan gum), and Salmonella enterica (O antigen). The S88 locus contained a four-gene operon for the biosynthesis of dTDP-L-rhamnose, an essential precursor for the sphingans. Unexpectedly, there were also two genes for secretion of a lytic or toxin-like protein nested within the polysaccharide cluster. The conservation and linkage of genes that code for a defensive capsule and genes for secretion of an offensive lysin or toxin suggest a heretofore unknown pathogenic life history for Sphingomonas strain S88.

ATP-Binding Cassette Transporters↗

PubMed1985

The in vitro interaction of naphthyridinomycin with deoxyribonucleic acids.

The binding of naphthyridinomycin (NAP) to deoxyribonucleic acid was investigated using radioisotope labeled antibiotic. Dithiothreitol (DTT) enhances complex formation in a concentration dependent fashion but was found to be slightly inhibitory at concentrations above 10 mM. [C3H3]-NAP-DNA complexes, formed in the presence or absence of reducing reagents, were stable to Sephadex G-25 chromatography and precipitation with ethanol, indicating a strong bond formed between the drug and DNA. Time course studies showed that the difference between the binding of activated and non-activated antibiotic was a DTT-dependent burst. This was followed by a second phase of binding which was similar in both the activated and non-activated antibiotics. The activation of the antibiotic by DTT was a reversible reaction at pH 7.9. The activated form at pH 5.0 was extremely stable and did not revert to the unactivated form even after an 8-h incubation period. Antibiotic-DNA complex formation was pH independent between pH 5.0 and 7.0 for activated NAP. The non-activated antibiotic bound to DNA much better at pH 5.0 than at physiological pH values. Release of antibiotic from complexes (as followed by long term dialysis) formed in the presence of DTT and at pH 5.0 was biphasic, suggesting that the drug can bind to DNA in more than one way. A constant rate of antibiotic release was observed at pH 7.9 with or without DTT. At pH 2.0 and pH 12.0, greater than 95% of the antibiotic is released from the complexes. Most of the acid released antibiotic is NAP while most of the base released antibiotic had decomposed to a more polar compound. NAP binds well to calf thymus DNA, poly(dG) . poly(dC), and T4 DNA but shows significantly less affinity for poly(dA) . poly(dT), poly(dA . dT) . poly(dA . dT), poly(dG), poly(dC), poly(dI) . poly(dC) or poly(dG . dC) . poly(dG . dC). This specificity of NAP for DNA is similar to that observed for the pyrrolo(1,4)benzodiazepine antibiotics and saframycin A and S; all of which bind to double stranded DNA through their carbinolamine or masked carbinolamine functionalities. Two mechanisms which can explain the need for activation of NAP are also proposed.

Animals↗

PubMedDate not supplied

Genetic engineering of structural protein polymers.

Genetic and protein engineering are components of a new polymer chemistry that provide the tools for producing macromolecular polyamide copolymers of diversity and precision far beyond the current capabilities of synthetic polymer chemistry. The genetic machinery allows molecular control of chemical and physical chain properties. Nature utilizes this control to formulate protein polymers into materials with extraordinary mechanical properties, such as the strength and toughness of silk and the elasticity and resilience of mammalian elastin. The properties of these materials have been attributed to the presence of short repeating oligopeptide sequences contained in the proteins, fibroin, and elastin. We have produced homoblock protein polymers consisting exclusively of silk-like crystalline blocks and elastin-like flexible blocks. We have demonstrated that each homoblock polymer as produced by microbial fermentation exhibits measurable properties of crystallinity and elasticity. Additionally, we have produced alternating block copolymers of various amounts of silk-like and elastin-like blocks, ranging from a ratio of 1:4 to 2:1, respectively. The crystallinity of each copolymer varies with the amount of crystalline block interruptions. The production of fiber materials with custom-engineered mechanical properties is a potential outcome of this technology.

Amino Acid Sequence↗