Grosser, D. | Search bioRxiv

bioRxiv2020

Insight into glycosphingolipid crypticity: Crystal structure of the anti-tumor antibody 14F7 and recognition of NeuGc GM3 ganglioside

Tumor-associated glycolipids such as NeuGc GM3 are auspicious molecular targets in antineoplastic therapies and vaccine strategies. 14F7 is an anti-tumor antibody with high clinical potential, which has extraordinary specificity for NeuGc GM3, but does not recognize the very similar, ubiquitous NeuAc GM3. Here we present the 2.3 [A] crystal structure of the 14F7 binding domain (14F7 scFv) in complex with the NeuGc GM3 trisaccharide. Intriguingly, a water molecule appears to shape the specificity of 14F7. Using model membrane systems, we show that 14F7 recognizes NeuGc GM3 only above lipid concentrations that are likely to form glycolipid-rich domains. This "all-or-nothing" effect was exacerbated in giant unilamellar vesicles and multilamellar vesicles, whereas no binding was observed to 100 nm liposomes, emphasizing that the 14F7-NeuGc GM3 interaction is additionally modulated by membrane curvature. Unexpectedly, adding NeuAc GM3 strongly increased binding affinity to NeuGc GM3-containing liposomes. This effect may be important for tumor recognition, where the ubiquitous NeuAc GM3 may enhance 14F7 binding to NeuGc GM3-expressing cancer cells.

biochemistry↗

bioRxiv2019

Minimal requirements for membrane adaptation of the bacterial model organism M. extorquens

Cells, from microbes to man, adapt their membranes in response to the environment to maintain their properties and functions. To adapt, lipid composition is homeostatically regulated to conserve optimal membrane properties. Global patterns of lipidome remodelling are poorly understood, particularly in model organisms with simple lipid compositions that can provide insight into fundamental principles underlying membrane adaptation. Using shotgun lipidomics, we examined the simple yet adaptive lipidome of the plant-associated Gram-negative bacterium Methylobacterium extorquens over varying temperature, hyperosmotic and detergent stress, carbon sources, and cell density. We observed that as few as ten lipids account for 90% of the total changes, thus constraining the upper limit of variable lipids required for an adaptive living membrane. Across all conditions, the highest degree of lipidomic variability was observed for changing growth temperature. We also revealed that variations in lipid structural features are not monotonic over a given range of conditions and are heterogeneous across lipid classes. Interestingly, phosphotidylcholine showed the most extreme acyl chain remodeling among all lipid classes, suggesting a new link to its importance in bacterial-host interactions and pathogenicity. These patterns in lipidomic remodeling suggest a highly adaptive mechanism with many degrees of freedom and constrain the lipidomic requirements for an adaptive membrane.

biochemistry↗