Role of polyamines in the binding of initiator tRNA to the 70S ribosomes of extreme thermophilic bacterium Calderobacterium hydrogenophilum

Insights into thermoadaptation and the evolution of mesophily from the bacterial phylum Thermotogae

Thermophiles are extremophiles that grow optimally at temperatures >45 °C. To survive and maintain function of their biological molecules, they have a suite of characteristics not found in organisms that grow at moderate temperature (mesophiles). At the cellular level, thermophiles have mechanisms for maintaining their membranes, nucleic acids, and other cellular structures. At the protein level, each of their proteins remains stable and retains activity at temperatures that would denature their mesophilic homologs. Conversely, cellular structures and proteins from thermophiles may not function optimally at moderate temperatures. These differences between thermophiles and mesophiles presumably present a barrier for evolutionary transitioning between the 2 lifestyles. Therefore, studying closely related thermophiles and mesophiles can help us determine how such lifestyle transitions may happen. The bacterial phylum Thermotogae contains hyperthermophiles, thermophiles, mesophiles, and organisms with temperature ranges wide enough to span both thermophilic and mesophilic temperatures. Genomic, proteomic, and physiological differences noted between other bacterial thermophiles and mesophiles are evident within the Thermotogae. We argue that the Thermotogae is an ideal group of organisms for understanding of the response to fluctuating temperature and of long-term evolutionary adaptation to a different growth temperature range.

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.