Biosynthesis of butirosin in Bacillus circulans NRRL B3312: identification by sequence analysis and insertional mutagenesis of the butB gene involved in antibiotic production

An Aminoglycoside Antibacterial Substance, S-137-R, Produced by Newly Isolated Bacillus velezensis Strain RP137 from the Persian Gulf

Given antibiotic resistance in pathogens, finding antibiotics from new sources is always a topic of interest to scientists. In the present study, among various isolates from the Persian Gulf coastal area, the strain RP137 was selected as producer of antibacterial compound. Morphological and biochemical studies along with 16S rDNA sequencing showed that strain RP137 belongs to Bacillus genus and was tentatively named Bacillus velezensis strain RP137. The effect of various carbon and nitrogen sources on optimizing the production of antibacterial compound showed that the low-cost rice starch and potassium nitrate supply to the strain RP137 caused producing of 86.0 ± 8.7 µg/mL extract having the antibacterial activity. The fractionation of the primary methanol extract in different solvents followed by reversed-phase HPLC obtained a pure antibacterial-active sample, S-137-R. Structural analysis of the purified S-137-R with the help of FTIR, HR-MS, ¹H-NMR, and ¹³C-NMR showed that the S-137-R compound is classified as aminoglycoside. Minimum inhibition concentration (MIC) of the pure compound for Gram-positive bacteria, Staphylococcus aureus and methicillin resistant Staphylococcus aureus, showed an average antibacterial effect of about 80 µg/mL and 150 µg/mL, respectively and for Pseudomonas aeruginosa (100 µg/mL), while having very little toxic effect on E. coli. Moreover, low cytotoxicity effect of the S-137-R on cancerous and normal cells as well as the low intensity of the hemolysis of red blood cells in higher concentrations of S-137-R make it an ideal candidate for further structure-activity relationship assessments towards its medical applications.

Probes and drugs that interfere with protein translation via targeting to the RNAs or RNA-protein interactions

Protein synthesis is critical to cell survival and translation regulation is essential to post-transcriptional gene expression regulation. Disorders of this process, particularly through RNA-binding proteins, is associated with the development and progression of a number of diseases, including cancers. However, the molecular mechanisms underlying the initiation of protein synthesis are intricate, making it difficult to find a drug that interferes with this process. Chemical probes are useful in elucidating the structures of RNA-protein complex and molecular mechanism of biological events. Moreover, some of these chemical probes show certain therapeutic benefits and can be further developed as leading compounds. Here, we will briefly review the general process and mechanism of protein synthesis, and emphasis on chemical probes in examples of probing the RNA structural changes and RNA-protein interactions. Moreover, the therapeutic potential of these probes is also discussed to give a comprehensive understanding.

LocateP: genome-scale subcellular-location predictor for bacterial proteins

Background

In the past decades, various protein subcellular-location (SCL) predictors have been developed. Most of these predictors, like TMHMM 2.0, SignalP 3.0, PrediSi and Phobius, aim at the identification of one or a few SCLs, whereas others such as CELLO and Psortb.v.2.0 aim at a broader classification. Although these tools and pipelines can achieve a high precision in the accurate prediction of signal peptides and transmembrane helices, they have a much lower accuracy when other sequence characteristics are concerned. For instance, it proved notoriously difficult to identify the fate of proteins carrying a putative type I signal peptidase (SPIase) cleavage site, as many of those proteins are retained in the cell membrane as N-terminally anchored membrane proteins. Moreover, most of the SCL classifiers are based on the classification of the Swiss-Prot database and consequently inherited the inconsistency of that SCL classification. As accurate and detailed SCL prediction on a genome scale is highly desired by experimental researchers, we decided to construct a new SCL prediction pipeline: LocateP.

Results

LocateP combines many of the existing high-precision SCL identifiers with our own newly developed identifiers for specific SCLs. The LocateP pipeline was designed such that it mimics protein targeting and secretion processes. It distinguishes 7 different SCLs within Gram-positive bacteria: intracellular, multi-transmembrane, N-terminally membrane anchored, C-terminally membrane anchored, lipid-anchored, LPxTG-type cell-wall anchored, and secreted/released proteins. Moreover, it distinguishes pathways for Sec- or Tat-dependent secretion and alternative secretion of bacteriocin-like proteins. The pipeline was tested on data sets extracted from literature, including experimental proteomics studies. The tests showed that LocateP performs as well as, or even slightly better than other SCL predictors for some locations and outperforms current tools especially where the N-terminally anchored and the SPIase-cleaved secreted proteins are concerned. Overall, the accuracy of LocateP was always higher than 90%. LocateP was then used to predict the SCLs of all proteins encoded by completed Gram-positive bacterial genomes. The results are stored in the database LocateP-DB [1].

Conclusion

LocateP is by far the most accurate and detailed protein SCL predictor for Gram-positive bacteria currently available.

Unique O-ribosylation in the biosynthesis of butirosin

Using a comparative genetics approach, one or more of the BtrA, BtrL, BtrP, and BtrV proteins encoded in the butirosin biosynthetic gene cluster (btr) from Bacillus circulans SANK72073 were identified as being responsible for an O-ribosylation process leading to the formation of ribostamycin, a key intermediate in this, and related antibiotic biosynthetic pathways. Functional analysis of the recombinantly expressed proteins revealed that both BtrL and BtrP were responsible for the ribosylation of neamine, using 5-phosphoribosyl-1-diphosphate (PRPP) as the ribosyl donor. Further detailed analysis indicated that this process occurs via two discrete steps: with BtrL first catalyzing the phosphoribosylaion of neamine to form 5''-phosphoribostamycin, followed by a BtrP-catalyzed dephosphorylation to generate ribostamycin. To the best of our knowledge, this is the first time that the functional characterization of a glycosyltransferase from an aminoglycoside biosynthetic gene cluster has been reported.

Biosynthesis of aminocyclitol-aminoglycoside antibiotics and related compounds

This review covers the biosynthesis of aminocyclitol-aminoglycoside antibiotics and related compounds, particularly from the molecular genetic perspectives. 195 references are cited.

Extended sequence and functional analysis of the butirosin biosynthetic gene cluster in Bacillus circulans SANK 72073

Butirosin produced by Bacillus circulans is among the clinically important 2-deoxystreptamine containing aminoglycoside antibiotics and its unique structure is found in (S)-4-amino-2-hydroxyburyric acid substituted at C-1 of 2-deoxystreptamine. Recently, the key part of the butirosin biosynthetic gene cluster has been identified from Bacillus circulans SANK 72073, however the whole gene for the biosynthesis awaited for identification. In the present study, we undertook extended analysis of the butirosin biosynthetic gene cluster and found nine additional open reading flames (ORFs), btrQ, btrR1, btrR2, btrT, btrU, btrV, btrW, btrX and orf1 in the cluster. In addition, we constructed disruption mutants of btrR1 and btrP-V, and found that the btr genes (ca. 24Kb) between btrR1 and btrP-V are at least required for the butirosin biosynthesis.