Effect of polypeptide initiation factors on the spermidine stimulation of initiation complex formation

Cell-free synthesis of functionally active HSPB5

Human αB-crystallin (HSPB5) is frequently modified post-translationally by UV radiation, oxidation, and age-associated processes, which complicates functional analyses of the protein using natural sources. Thus, determining the biological function of HSPB5 at the molecular structure level requires unmodified protein. Here, we employed an Escherichia coli cell-free protein synthesis system to prepare unmodified, functionally active human HSPB5. An S30 extract prepared from E. coli strain BL21 (DE3) was used for HSPB5 synthesis. The efficacy of protein synthesis was assessed by monitoring influencing factors, such as the concentrations of Mg2+ and other reaction mixture constituents, and by evaluating batch and/or dialysis synthesis systems. Chaperone-like activity of synthesized HSPB5 was assayed using alcohol dehydrogenase (ADH) under thermal stress. The amount of HSPB5 synthesized using the cell-free system depended significantly on the concentration of Mg2+ in the reaction mixture. Use of condensed S30 extract and increased levels of amino acids promoted HSPB5 production. Compared with the batch system, HSPB5 synthesis was markedly increased using the dialysis system. The construction vector played a critical role in regulating the efficacy of protein synthesis. HSPB5 synthesized using the cell-free system had a native molecular mass, as determined by mass spectrometry analysis. The co-presence of synthesized HSPB5 suppressed heat-associated denaturation of ADH. Human HSPB5 synthesized using the cell-free system thus retains functional activity as a molecular chaperone.

Effects of ethyl and benzyl analogues of spermine on Escherichia coli peptidyltransferase activity, polyamine transport, and cellular growth

Various ethyl and benzyl spermine analogues, including the anticancer agent N1,N12-bis(ethyl)spermine, were studied for their ability to affect the growth of cultured Escherichia coli cells, to inhibit [3H]putrescine and [3H]spermine uptake into cells, and to modulate the peptidyltransferase activity (EC 2. 3. 2. 12). Relative to other cell lines, growth of E. coli was uniquely insensitive to these analogues. Nevertheless, these analogues conferred similar modulation of in vitro protein synthesis and inhibition of [3H]putrescine and [3H]spermine uptake, as is seen in other cell types. Thus, both ethyl and benzyl analogues of spermine not only promote the formation and stabilization of the initiator ribosomal ternary complex, but they also have a sparing effect on the Mg2+ requirements. Also, in a complete cell-free protein-synthesizing system, these analogues at low concentrations stimulated peptide bond formation, whereas at higher concentrations, they inhibited the reaction. The ranking order for stimulation of peptide-bond formation by the analogues was N4,N9-dibenzylspermine > N4, N9-bis(ethyl)spermine congruent with N1-ethylspermine > N1, N12-bis(ethyl)spermine, whereas the order of analogue potency regarding the inhibitory effect was inverted, with inhibition constant values of 10, 3.1, 1.5, and 0.98 microM, respectively. Although the above analogues failed to interact with the putrescine-specific uptake system, they exhibited high affinity for the polyamine uptake system encoded by the potABCD operon. Despite this fact, none of the analogues could be internalized by the polyamine transport system, and therefore they could not influence the intracellular polyamine pools and growth of E. coli cells.

A highly efficient cell-free protein synthesis system from Escherichia coli

We modified a cell-free coupled transcription/translation system from Escherichia coli with the T7 phage RNA polymerase, and achieved a productivity as high as 0.4 mg protein/ml reaction mixture. First, we found that the optimal concentrations of phosphoenolpyruvate and poly(ethylene glycol) are interdependent; higher concentrations of the former should be used at higher concentrations of the latter. Second, the use of a condensed 30000 x g cell extract, in place of the conventional one, significantly increased the initial rate of protein synthesis. This phenomenon was demonstrated to be due to a reason other than elimination of inhibitory molecule(s) from the extract. For this system with the condensed extract, the phosphoenolpyruvate and poly(ethylene glycol) concentrations were again co-optimized, resulting in production of chloramphenicol acetyltransferase at a productivity of 0.3 mg/ml. Finally, the productivity was further increased up to 0.4 mg/ml, by supplementation of the pool of amino acids. This improved cell-free protein synthesis system is superior in productivity to any other cell-free systems reported so far, including the continuous-flow cell-free system.

Serum albumin

The liver manufactures albumin at a massive rate and decreases production in times of environmental, nutritional, toxic and trauma stress. Osmotic pressure is a basic evolutionary regulatory factor, and hormonal control over albumin production has been demonstrated. Where and why new or old albumin is degraded are questions which have not been clarified, although the vascular endothelium may well be the degradative site. Albumin is important as a transport protein, as a measure of evolution and as a model to study secretion following synthesis without the intervening steps of glycosylation. Investigations as to how this protein enters the endoplasmic membrane may well answer some of the questions concerning signal peptide insertion (288). The role of the urea cycle intermediate ornithine and its participation in polyamine synthesis, which has a positive effect on albumin synthesis, is under study. Likewise, the inverse relation between acute-phase protein synthesis and albumin synthesis regulated by interleukin 1 and other cytokines will merit further study. These are a few of the concepts which will be tested in the future.

Preferential stimulation of the in vivo synthesis of a protein by polyamines in Escherichia coli: purification and properties of the specific protein

The possibility that polyamines can stimulate the synthesis of special kinds of proteins has been examined by using a polyamine-requiring mutant of Escherichia coli. It was found that the synthesis of some proteins, particularly one with a molecular weight (Mr) of 62K, was significantly stimulated following polyamine supplementation of polyamine-starved cells. The preferential stimulation of the synthesis of this polyamine-induced protein of Mr 62K (PI protein) was followed by the stimulation of overall protein synthesis by polyamines. PI protein was purified to homogeneity and some of its properties were examined. From studies on the effect of PI protein on MS2 RNA directed protein synthesis, it was shown that this protein stimulated the synthesis of RNA replicase by 2.2-fold in the presence of 1 mM spermidine.

Effects of nutrition and alcohol on albumin synthesis

Albumin synthesis was studied in the isolated perfused rabbit liver under the influence of the stresses of fasting and acute alcohol and acetaldehyde exposure. Fasting clearly depressed albumin production and disaggregated the endoplasmic membrane-bound polysomes. Acute exposure to alcohol produced the same results. Acetaldehyde 2 mg% resulted in a depression of albumin synthesis but the polysomes were not disaggregated. The metabolism of alcohol was necessary for polysome disaggregation. The acute effects of ethanol and fasting were quite similar and it might be considered that the alcohol was acting like a pharmacologic fast. Employing the liver from a fasted donor specific amino acids infused into the liver at levels of 10 mM reversed the acute effects of fasting and the acute effects of exposure to ethanol. However when the two stresses of fasting and alcohol were combined the same amino acids were not effective. In studying albumin synthesis and/or secretion it is necessary to carefully define the nutritional status of the experimental model.

Differential stimulation by polyamines of phage RNA-directed synthesis of proteins

The effect of polyamines on Q beta and MS2 phage RNA-directed synthesis of three kinds of protein in an Escherichia coli cell-free system has been studied. With both phage RNAs, the degree of stimulation of protein synthesis by spermidine was in the order RNA replicase greater than A protein, while the synthesis of coat protein was not stimulated significantly by spermidine. The synthesis of RNA replicase was stimulated by 1 mM spermidine approx. 8-fold. From the results of Q beta RNA direct alanyl-tRNA and seryl-tRNA binding to ribosomes and initiation dipeptide synthesis, it is suggested that the preferential stimulation of the synthesis of RNA replicase by spermidine is due at least partially to the stimulation of the initiation of RNA replicase synthesis.

Purification and properties of fMet-tRNAf deacylase from Escherichia coli

A formylmethionyl-tRNAf deacylase has been purified about 330-fold from a crude initiation factor preparation (1 M NH4Cl ribosomal wash) from Escherichia coli Q13. The enzyme was nearly homogeneous and had an apparent molecular weight of 24 000. Rat liver methionyl-tRNAf and E. coli methionyl-tRNAm were not hydrolyzed significantly by the enzyme under standard conditions. Q beta RNA- and AUG(A)n-directed polypeptide synthesis was inhibited by the enzyme. The inhibition was at the level of initiation of polypeptide synthesis. The enzymatic activity was inhibited by various factors necessary for polypeptide synthesis. The activity was inhibited more by NH4Cl and spermidine than by Mg2+, GTP and ATP. The complex of formylmethionyl-tRNAf, initiation factor 2 and GTP was resistant to enzymatic hydrolysis, and the resistance was enhanced by the addition of AUG and ribosomes to the above reaction mixture.