Combining the biological specificity of fluorescence microscopy with topographical features revealed by atomic force microscopy (AFM) provides new insights into cell biology. However, the lack of systematic alignment capabilities especially in scanning-tip AFM has limited the combined application approach as AFM drift leads to increasing image mismatch over time. We present an alignment correction method using the cantilever tip as a reference landmark. Since the precise tip position is known in both the fluorescence and AFM images, exact re-alignment becomes possible. We used beads to demonstrate the validity of the method in a complex artificial sample. We then extended this method to biological samples to depict membrane structures in fixed and living human fibroblasts. We were able to map nanoscale membrane structures, such as clathrin-coated pits, to their respective fluorescent spots. Reliable alignment between fluorescence signals and topographic structures opens possibilities to assess key biological processes at the cell surface such as endocytosis and exocytosis.

Efficient uptake and channelling of long-chain fatty acids (LCFA) are critical cell functions. Evidence is emerging that proteins are important mediators of LCFA-trafficking into cells and various proteins have been suggested to be involved in this process. Amongst these proteins is a family of membrane-associated proteins termed fatty acid transport proteins (FATP). So far six members of this family, designated FATP 1–6, have been characterized. FATP 1, 2 and 6 show a highly-conserved AMP-binding region that participates in the activation of very-long-chain fatty acids (VLCFA) to form their acyl-CoA derivatives. The mechanisms by which FATP mediate LCFA uptake are not well understood, but several studies provide evidence that uptake of LCFA across cellular membranes is closely linked to acyl-CoA synthetase activity. It is proposed that FATP indirectly enhance LCFA uptake by activating VLCFA to their CoA esters, which are required to maintain the typical structure of lipid rafts in cellular membranes. Recent work has shown that the structural integrity of lipid rafts is essential for cellular LCFA uptake. This effect might be exerted by proteins, e.g. caveolin-1 and FAT/CD36, that use lipid rafts as platforms and bind or transport LCFA. The proposed molecular mechanisms await further experimental investigation.