Mycobacteria, including persistent pathogens like Mycobacterium tuberculosis, have an unusual membrane structure in which, outside the plasma membrane, a nonfluid hydrophobic fatty acid layer supports a fluid monolayer rich in glycolipids such as trehalose 6,6'-dimycolate (TDM; cord factor). Given the abilities of mycobacteria to survive desiccation and trehalose in solution to protect biomolecules and whole organisms during freezing, drying, and other stresses, we hypothesized that TDM alone may suffice to confer dehydration resistance to the membranes of which it is a constituent. We devised an experimental model that mimics the structure of mycobacterial envelopes in which an immobile hydrophobic layer supports a TDM-rich, two-dimensionally fluid leaflet. We have found that TDM monolayers, in stark contrast to phospholipid membranes, can be dehydrated and rehydrated without loss of integrity, as assessed by fluidity and protein binding. Strikingly, this protection from dehydration extends to TDM-phospholipid mixtures with as little as 25 mol % TDM. The dependence of the recovery of membrane mobility upon rehydration on TDM fraction shows a functional form indicative of spatial percolation, implying that the connectivity of TDM plays a crucial role in membrane preservation. Our observations are the first reported instance of dehydration resistance provided by a membrane glycolipid.

The authors wish to note the following: "We have determined that the conclusions stated in our paper are an artifact of errors of analysis. Our methods involved determining the rheological properties of lipid bilayers from analysis of the trajectories of lipid-anchored particles. Errors related to the particle-tracking methods we used generated an artifactual elastic-like signature."The imprecision in tracking resulted from determining the position of each particle by fitting the logarithm of the particle's intensity profile to a quadratic function. Directly fitting the intensity to a Gaussian form is considerably less sensitive to noise and signal intensity. This improved fitting reduces positional uncertainty in test images from around 30 nm to a few nm and, applied to our membrane data, completely eliminates the 'elastic' response. Moreover, adding 30 nm of random error to precisely tracked images reproduces the reported elastic signature. Therefore, our data indicate that lipid membranes show a purely viscous character over the entire frequency range examined. Our initial assessments of particle tracking algorithms were not sufficiently stringent, leading to an overestimate of our tracking precision and the use of inadequate fitting methods."The artifactual elastic response we reported showed a feature at the chain ordering transition temperature of the lipid membranes examined. We are not certain what aspect of the images, when imprecisely tracked, led to this feature. We suspect that motions of the particles perpendicular to the membrane plane may be responsible."The conclusions of the paper are wrong and, regrettably, we must retract the work. We sincerely apologize for any confusion that our report may have caused."

Lipid derived desiccation resistance in membranes is a rare and unique ability previously observed only with trehalose dimycolate (TDM), an abundant mycobacterial glycolipid. Here we present the first synthetic trehalose glycolipids capable of providing desiccation protection to membranes of which they are constituents. The synthetic glycolipids consist of a simple trehalose disaccharide headgroup, similar to TDM, with hydrophobic tail groups of two 15 or 18 carbon chains. The synthetic trehalose glycolipids protected supported monolayers of phospholipids against dehydration even as minority components of the overall membrane, down to as little as 20 mol % trehalose glycolipid, as assessed by assays of membrane fluidity. The dependence of the desiccation protection on synthetic trehalose glycolipid fraction is nearly identical to that of TDM. The striking similarity of the desiccation resistance observed with TDM and the synthetic trehalose glycolipids, despite the variety of hydrophobic tail structures employed, suggests interactions between the trehalose headgroup and surrounding molecules are the determining factor in dehydration protection.

No abstract

predicted to be 1/3 [Gomez et al., Saeki et al.] or 1/4 [Yanagisawa et al.]. The power law exponent has been measured previously for liquid domains in vesicle membranes as 0.15 [Saeki et al.] and 2/3 [Yanagisawa et al.]. Here we present an independent measurement of the power law exponent.