The influence of temperature and membrane-fluidity changes on the olfactory adenylate cyclase of the rat

A systematic framework for using membrane metrics for strain engineering

The cell membrane plays a central role in the fitness and performance of microbial cell factories and therefore it is an attractive engineering target. The goal of this work is to develop a systematic framework for identifying membrane features for use as engineering targets. The metrics that describe the composition of the membrane can be visualized as "knobs" that modulate various "outcomes", such as physical properties of the membrane and metabolic activity in the form of growth and productivity, with these relationships varying depending on the condition. We generated a set of strains with altered membrane lipid composition via expression of des, fabA and fabB and performed a rigorous characterization of these knobs and outcomes across several individual inhibitory conditions. Here, the knobs are the relative abundance of unsaturated lipids and lipids containing cyclic rings; the average lipid length, and the ratio of linear and non-linear lipids (L/nL ratio). The outcomes are membrane permeability, hydrophobicity, fluidity, and specific growth rate. This characterization identified significant correlations between knobs and outcomes that were specific to individual inhibitors, but also were significant across all tested conditions. For example, across all conditions, the L/nL ratio is positively correlated with the cell surface hydrophobicity, and the average lipid length is positively correlated with specific growth rate. A subsequent analysis of the data with the individual inhibitors identified pairs of lipid metrics and membrane properties that were predicted to impact cell growth in seven modeled scenarios with two or more inhibitors. The L/nL ratio and the membrane hydrophobicity were predicted to impact cell growth with the highest frequency. We experimentally validated this prediction in the combined condition of 42 °C, 2.5 mM furfural and 2% v/v ethanol in minimal media. Membrane hydrophobicity was confirmed to be a significant predictor of ethanol production. This work demonstrates that membrane physical properties can be used to predict the performance of biocatalysts in single and multiple inhibitory conditions, and possibly as an engineering target. In this manner, membrane properties can possibly be used as screening or selection metrics for library- or evolution-based strain engineering.

Enhancement of adenylate cyclase activity in S49 lymphoma cell membranes by the toxin thionin from Pyrularia pubera

We investigated the mode of action of Pyrularia thionin on adenylate cyclase in S49 lymphoma cell membranes. Thionin increased the forskolin-induced cAMP production in both wild-type and cyc- variant cell membranes. Thionin increased the apparent efficacy, but not potency, of the stimulation of adenylate cyclase by forskolin. Our results also indicated that the stimulatory G protein (Gs) was not involved in the action of thionin on adenylate cyclase; however, thionin appeared to reduce the effect of Gi on adenylate cyclase. We examined the effect of thionin on the temperature dependence of adenylate cyclase activity. The effect of thionin was not quantitatively the same at all temperatures. The effect was greatest in the range of about 30 degrees C to 50 degrees C. In addition, cardiotoxin, a structurally distinct peptide that alters the properties of biological membranes similarly to thionin, also enhanced the activity of adenylate cyclase. It seems reasonable to suspect that thionin influences the activity of adenylate cyclase indirectly by acting on the membrane.

Ceratitis capitata brain adenylate cyclase and its membrane environment

Adenylate cyclase activation by GTP and octopamine as well as basal activity (in the presence of Mg2+) have been studied as a function of membrane structure in plasma membranes from brain of the dipterous Ceratitis capitata. Benzyl alcohol and lidocaine, but not phenobarbital, inhibited the three activities to the same extent. Triton X-100-solubilized adenylate cyclase was also inhibited by benzyl alcohol and lidocaine, but not by phenobarbital. Results could be explained by an effect on the catalytic unit lipid environment, which would be maintained after solubilization, counteracting the effect of these drugs to facilitate lateral diffusion and coupling of adenylate cyclase components in the lipid bilayer. The observation that the insect adenylate cyclase is relatively insensitive to changes in bulk bilayer fluidity is strengthened by the absence of effect of phenobarbital on enzyme activities. Indeed, this compound was as active as lidocaine or benzyl alcohol in increasing bulk membrane fluidity. The response of C. capitata adenylate cyclase to changes in membrane fluidity is different from that recorded in mammalian systems. This may be functionally important and result from the fact that insects are not warm-blooded.

Effect of in vivo modulation of membrane docosahexaenoic acid levels on the dopamine-dependent adenylate cyclase activity in the rat retina

We have studied the effect of a dietary deprivation of n-3 fatty acids on the activity of the dopamine (DA)-dependent adenylate cyclase in the rat retina. Experiments were conducted in 6-month-old rats raised on semipurified diets containing either safflower oil (n-3 deficient diet) or soybean oil (control diet). The levels of docosahexaenoic acid [22:6 (n-3)] in retinal phospholipids were significantly decreased in n-3 deficient rats (35-42% of control levels). This was compensated by a rise in 22:5 (n-6), the total content of polyunsaturated fatty acids (PUFA) remaining approximately constant. Adenylate cyclase activity was measured in retinal membrane preparations from dark-adapted or light-exposed rats. The enzyme activity was stimulated by DA and SKF 38393 in a light-dependent fashion. The activation was lower in rats exposed to light than in dark-adapted animals, suggesting a down-regulation of the D1 DA receptors by light. The activation by guanine nucleotides and forskolin was also decreased in light-exposed rats. There was no significant effect of the dietary regimen on the various adenylate cyclase activities and their response to light. Furthermore, the guanine nucleotide- and DA-dependent adenylate cyclase activities of retinal membranes were found to be relatively resistant to changes in membrane fluidity induced in vitro by benzyl alcohol. The results indicate that in the absence of changes in total PUFA content, a decreased ratio of n-3 to n-6 fatty acids in membrane phospholipids does not significantly affect the properties of adenylate cyclase in the rat retina.