Translation initiation defects in ribosomes from streptomycin dependent strains

Truncated antimicrobial peptides from marine organisms retain anticancer activity and antibacterial activity against multidrug-resistant Staphylococcus aureus

Antimicrobial peptides (AMPs) were recently determined to be potential candidates for treating drug-resistant bacterial infections. The aim of this study was to develop shorter AMP fragments that combine maximal bactericidal effect with minimal synthesis cost. We first synthesized a series of truncated forms of AMPs (anti-lipopolysaccharide factor from shrimp, epinecidin from grouper, and pardaxin from Pardachirus marmoratus). The minimum inhibitory concentrations (MICs) of modified AMPs against ten bacterial species were determined. We also examined the synergy between peptide and non-peptide antibiotics. In addition, we measured the inhibitory rate of cancer cells treated with AMPs by MTS assay. We found that two modified antibacterial peptides (epinecidin-8 and pardaxin-6) had a broad range of action against both gram-positive and gram-negative bacteria. Furthermore, epinecidin and pardaxin were demonstrated to have high antibacterial and anticancer activities, and both AMPs resulted in a significant synergistic improvement in the potencies of streptomycin and kanamycin against methicillin-resistant Staphylococcus aureus. Neither AMP induced significant hemolysis at their MICs. In addition, both AMPs inhibited human epithelial carcinoma (HeLa) and fibrosarcoma (HT-1080) cell growth. The functions of these truncated AMPs were similar to those of their full-length equivalents. In conclusion, we have successfully identified shorter, inexpensive fragments with maximal bactericidal activity. This study also provides an excellent basis for the investigation of potential synergies between peptide and non-peptide antibiotics, for a broad range of antimicrobial and anticancer activities.

Speed-accuracy relationships during in vitro and in vivo protein biosynthesis

Poly U-directed incorporation of phenylalanine and leucine into polypeptide has been described in at least 50 papers since 1961. In general, high translation activities are associated with high accuracies, and vice-versa. Moreover, a vast body of independent experimental data (effect of ethanol, temperature, urea, aminoglycosides, etc... on protein synthesis) put together here suggests that, in many circumstances, speed and accuracy of elongation are correlated. This result is to be contrasted with the view that the speed and the fidelity of protein synthesis are two opposing parameters. In this report, recent experimental data on the nature and effect of ribosomal ambiguity (ram) and streptomycin resistance (Strr) mutations are reexamined. Models on the action of streptomycin and other misreading-inducing antibiotics, as well as long-standing ideas on the control of misreading in mammalian systems are critically evaluated. An explanation is provided for the long-befuddling data on the action of gentamicin.

Function of individual E. coli 30 S ribosomal proteins as determined by in situ immunospecific neutralization: a tentative classification

The accessibility of each 30S subunit protein to their cognate antibodies (IgG or Fabs) having been previously well established, the effect of their in situ specific neutralization by monovalent IgG fragments (FabI) are reported for five reactions: 1) T4 and R17 RNA directed protein synthesis: 2) polyphenylalanine synthesis: 3) enzymatic Phe-tRNA binding in the presence of 30S + 50W subunits: 4) fMet-tRNAf binding to the 30S subunit in the presence of initiation factors IF1, IF2, IF3; 5) coupling with lambda plac DNA transcription of the initial translation step (i.e., interaction of IF3 activated 30S subunits with nascent mRNA, in the absence of tRNA). According to evident similarities in their inhibition pattern concerning the five reactions tested, 30S subunit proteins can be classified in five categories which are discussed in terms of functional topography.

Erythromycin resistant mutations in Bacillus subtilis cause temperature sensitive sporulation

All of several hundred erythromycin resistant single site mutants of Bacillus subtilis W168 are temperature senstive for sporulation. The mutants and wild type cells grow vegetatively at essentially the same rates at both permissive (30 degrees C) and nonpermissive (47 degrees C) temperatures. In addition cellular protein synthesis, cell mass increases and cell viabilities are similar in mutant and wild type strains for several hours after the end of vegetative growth (47 degrees C). in the mutants examined, the temperature sensitive periods begin when the sporulation process is approximately 40% completed, and end when the process is 90% completed. At nonpermissive temperatures, the mutants produce serine and metal proteases at 50% of the wild type rate, accumulate serine esterase at 16% of the wild type rate, and do not demonstrate a sporulation related increase in alkaline phosphatase activity. The eryR and spots phenotypes cotransform 100%, and cotransduce 100% using phage PBS1. Revertants selected for ability to sporulate normally at 47 degrees C (spot), simultaneously regain parental sensitivity to erthromycin. No second site revertants are found. Ribosomes from eryR spots strains bind erythromycin at less than 1% of the wild type rate. A single 50S protein (L17) from mutant ribosomes shows an altered electrophoretic mobility. Ribosomes from spo+ revertants bind erythromycin like parental ribosomes and their proteins are electrophoretically identical to wild type. These data indicate that the L17 protein of the 50S ribosomal subunit from Bacillus subtilis may participate specifically in the sporulation process.

Selective messenger translation by Bacillus subtilis ribosomes

The in vitro B. subtilis protein synthesizing system is very restricted in its ability to translate E. coli phage messenger RNA's, specifically phage T4 RNA, even though it actively translates its proper mRNA species. In contrast, the E. coli system translates with similar efficiency mRNA from either source. The initiation factors from the two systems are functionally interchangeable. The 30S B. subtilis ribosomal subunit is responsible for the limited template specificity of the B. subtilis ribosomes. Although the efficiency of the T4RNA directed F Met-tRNA binding by B. subtilis ribosomes is less than that of SPOI RNA-directed binding, the most restrictive step in the translation of T4RNA by B. subtilis ribosomes appears to be at the level of the formation of the first peptide bond, as measured by F Metpuromycin formation.

Function of individual 30S subunit proteins of Escherichia coli. Effect of specific immunoglobulin fragments (Fab) on activities of ribosomal decoding sites

Specific anti-30S protein immunoglobulin G fragments (Fab) were used to determine the contribution of each of the 30S ribosomal proteins to: (1) polyphenylalanine synthesis, (2) initiation factor-dependent binding of fMet-tRNA, (3) T-factor-dependent binding of phenylalanyl-tRNA, and (4) fixation of radioactive dihydrostreptomycin. Twenty of the 21 possible antibodies (antibody against S17 excepted) were used. In conditions where all the 30S proteins were accessible to Fabs, all of these monovalent antibodies strongly inhibited polyphenylalanine synthesis in vitro. Antibodies against S4, S6, S7, S12, S15, and S16, however, showed a weaker effect.30S proteins can be classified into four categories by their contributions to the function of sites "A" and "P": class I appears nonessential for tRNA positioning at either site (S4, S7, S15, and S16); class II includes proteins whose role in initiation is critical (S2, S5, S6, S12, and S13); class III (S8, S9, S11, and S18) corresponds to proteins whose blockade prevents internal (elongation factor Tudependent) positioning; and class IV includes entities that are essential for activities of both "A" and "P" sites (S1, S3, S10, S14, S19, S20, and S21). Dihydrostreptomycin fixation to the 30S or 70S ribosomes was inhibited by antibodies against S1, S10, S11, S18, S19, S20, and S21, but only weakly by the anti-S12 (Str A protein) Fab. The significance of these results is discussed in relation to 30S protein function, heterogeneity, and topography.