Lateral organization of cell matrix proteins on the nano-scale
Cellular anchors are large accumulations of a multitude of multi-functional proteins and are known as focal adhesion sites. In this work, the spatial organization of a subset of cell-matrix proteins was analyzed, using the superresolution microscopy technique PALM. It was demonstrated, that all cellmatrix proteins form distinct areas of varying densities inside single focal adhesions. Highly dense protein accumulations can contain up to several tens of molecules and can span a diameter of more
... a diameter of more than hundred nanometers. However, no recognizable structure or polarity could be observed for such large protein accumulations. In order to study the temporal alterations and formation of such highly dense protein accumulations, the dynamic behavior of the adhesion receptor β3-integrin was analyzed. It was shown, that force inhibition can induce structural rearrangements, also leading to the redistribution of the density inside adhesion sites. However, force inhibition did not cause the complete disassembly of dense β3-integrin domains. Therefore, it is suggested that force can modulate the dense areas, but is not the initial inducer. Instead, it seems that an initial formation of dense domains occurs already in the very beginning of focal adhesion development, followed by a gradual immobilization of β3-integrin and thus leading to the formation of new adhesion sites. It was observed that the seed for some dense domains can be planted already in early maturation stages with the potential to increase its size upon adhesion expansion. Dense domains could even have a particular signaling function, as it was shown that the signaling protein FAK is primarily recruited to delimited areas inside focal adhesions, which could represent dense domains.