Luladey Ayalew
CHM 548-ARTICLE SUMMARY 1
Introduction-The effects of sterols on biological membranes have been extensively studied and has ordering properties. These properties of sterols allow membranes to have more fluidity and to from microdomains. Due to prokaryote absence of sterol molecules, any membrane-ordering properties have not been examined. Prokaryotes do however contain hopanoids, which are structurally similar to sterols. In this study, hopanoid’s effects on membrane structure are examined in prokaryotic membranes and compared with sterols. The authors hypothesized that the hopanoid, diplopterol (Dip), will function similarly to sterols in modulating the ordering lipids in membranes. Diplopterol Inhibits SM Gel State - Due …show more content…
Next the authors begin to examine a new lipid in order to determine if these effects that diplopterol can cause on lipids in membranes could have a physiological role in prokaryotes. Lipid A is structurally similar to sphingomyelin and is a known major component of the outer membranes of bacteria, which is the major location of diplopterol. Lipid A is also known to be effected by pH changes, undergoing phase changes to become less fluid with more of a gel state. Using the previous data and the known characteristics of Lipid A the authors hypothesized that a function of diplopterol in bacterial membranes can be to maintain the lipid states under varied conditions, like pH changes. To begin the isotherm plots from monolayer consisting of either Lipid A alone, Lipid A/Dip, or Lipid A/Chol are determined using a Langmuir trough instrument at varying pH conditions. At neutral pH Lipid A alone, Lipid A/Dip, and Lipid A/ Chol all lack an inflection point indicating no phase transition and Lo state is maintained. The shift to the right in the graph of Lipid A/Chol and Lipid A/Dip mixtures do however show an increase in condensation compared to the monolayer of Lipid A alone. At lower pH condition of 5.1 and 3.1 the monolayer of Lipid A alone do show an inflection point, indicating a …show more content…
The authors were able to show that diplopterol was able to inhibit the formation of gel state formation of SM and induce ordering of SM into a Lo state, similar to cholesterol. The confocal imaging was also able to show that separation of Ld and Lo regions in a membrane was obtained in the presence of diplopterol. Also, the diplopterol was shown to decrease the rate of diffusion, meaning the lipid molecules are moving slower due to the increased ordering of the structure. All these results indicated a similar function in cholesterol and diplopterol. The Lipid A ordering effect studies gave these abilities of diplopterol a physiological function, by showing that diplopterol can be used to decrease the changes in phases that can occur to do changes in the environment such as pH