The biological significance of differences in cows and sows colostrum and milk composition

The objective of this work was to compare the composition of colostrum and milk of cows and sows (content of dry matter, protein, milk fat and lactose, concentration of IGF-I and insulin) in samples taken on the first, second, third and seventh day after parturition, and then based on the differences in composition to determine a biological significance of nutrition of newborn during the earliest stages of their life. The investigation inluded 14 cows of Holstein breed and 14 sows of Landrace breed. The content of dry matter and the concentration of proteins in both colostrum and milk samples were statistically significantly higher in regard to sows mammary glands secretion, taken on the first day after the parturition (p<0,01 and p<0,001, individually), but their decrease in mammary glands secretion was more pronounced in the cows than the sows, during the first seven days. The concentration IGF-I was statistically significantly higher in the cows colostrum and milk in regard to the sows during the whole investigation period, while the concentration of insulin was significantly higher in the sows in regard to the cows during the same period. The concentrations of milk fat and lactose in cows milk samples were significantly lower in regard to the sows in all period of the study. On the basis of the obtained results, it can be concluded that there are significant differences in the composition of milk and colostrum of both the investigated animal species. The differences are probably the result of evolutionary adaptation of mammal gland function to nutrition, energy and protection requirements of these young animals in their early postnatal life. [Projekat Ministarstva nauke Republike Srbije, br. III 46002

rRNA methyltransferases and their role in resistance to antibiotics

Metiltransferaze (MTaze), koje čine veliku proteinsku superfamiliju, kao donatora metil grupe najčešće koriste S-adenozil-L-metionin (SAM). SAM-zavisne MTaze metiluju nukleinske kiseline (DNK, RNK) i proteine, modulišući tako njihovu aktivnost, funkciju i strukturnu organizaciju. Metilacija G1405 ili A1408 baza u 16S rRNK mikroorganizama koji proizvode aminoglikozide obezbeđuje rezistenciju na sopstvene toksične proizvode. Ovaj mehanizam rezistencije je donedavno bio opisan samo kod proizvođača antibiotika. Od 2003. godine i kod patogenih bakterija beleži se neprestan porast rezistencije na aminoglikozide putem ovog mehanizma, što predstavlja veliku pretnju efikasnoj upotrebi aminoglikozida u kliničkoj praksi. Jedno od mogućih rešenja problema leži u razvoju novih jedinjenja koja bi efikasno delovala na nova mesta u okviru ribozoma. Drugi pristup rešavanju ovog problema uključuje razvoj inhibitora MTaza odgovornih za rezistenciju, sa idejom da se onemogući modifikacija bakterijske rRNK i na taj način vrati terapeutska efikasnost postojećim aminoglikozidima. Fundamentalna istraživanja vezana za proteinsku ekspresiju, potpuno razumevanje mehanizma rezistencije kao i razrešenje tercijarne strukture proteina su neophodan preduslov za primenu inhibitora 16S rRNK MTaza u medicini.Methyltransferases (MTases), a large protein superfamily, commonly use S-adenosyl-L-methionine (SAM) as the methyl group donor. SAM-dependant MTases methylate both nucleic acids (DNA, RNA) and proteins, and thus modulate their activity, function and folding. Methylation of G1405 or A1408 nucleotides of 16S rRNA in aminoglycoside-producing microorganisms confers the resistance to their own toxic product(s). This mechanism of resistance has been considered as unique to antibiotics producers until recently. Since 2003, methylation of 16S rRNA as a mechanism of resistance is increasingly emerging in pathogenic bacteria. This represents a major threat towards the usefulness of aminoglycosides in the clinical practice. A potential solution to the problem involves the design of novel compounds that would act against new ribosomal targets. The second approach to the issue includes the development of resistance MTases' inhibitors, with the idea to prevent them from modifying the bacterial rRNA, and thus reinstate the therapeutic power of existing aminoglycosides. As the latter approach has considerable potential, it is obvious that fundamental research related to protein expression, in-depth understanding of the mechanism of action and resolving a tertiary structure of 16S rRNAs MTases are prerequisites for application in medicine

New polyene macrolide family produced by submerged culture of Streptomyces durmitorensis

A new polyene macrolide family, closely related to the pentaene macrolide antibiotic roflamycoin, was isolated from the both fermentation broth and biomass of Streptomyces durmitorensis wild-type strain MS405. The main compound was identified by NMR and Fourier transform ion cyclotron resonance mass spectrometry as 32,33-didehydroroflamycoin (1; DDHR). Additional four structurally related compounds were determined solely by MS analysis. DDHR induces cell death by apoptosis in various cancer cell lines as demonstrated by DNA fragmentation. Striking feature of DDHR is its internal fluorescence allowing visualization of labeled plasma membranes and internal membrane structures. The Journal of Antibiotics (2011) 64, 717-722; doi:10.1038/ja.2011.81; published online 14 September 201

Heterologous Escherichia coli Expression, Purification and Characterization of the GrmA Aminoglycoside-Resistance Methyltransferase

The mechanism of resistance to aminoglycosides based on methylation of their target, 16S rRNA, was until recently described only in antibiotic producing microorganisms. However, equivalent methyltransferases have now also been identified among numerous clinical Gram-negative pathogenic isolates. We have cloned, expressed, and purified GrmA, the aminoglycoside-resistance methyltransferase from Micromonospora purpurea, producer of gentamicin complex. Two vectors were created that express protein with an N-terminal 6x histidine tag with and without an enterokinase recognition producing proteins His(6)-EK-GrmA and His(6)-GrmA, respectively. The activity of both recombinant proteins was demonstrated in vivo. After optimized expression and native purification both protein variants proved to be active in in vitro methylation assays. This work lays a foundation for future detailed biochemical, structural and pharmacological studies with this member of an important group of aminoglycoside-resistance enzymes