**7. Concluding Remarks**

Can we define a common denominator for the function of FAS1 proteins? The characterization of HsTgfbi structure and function demonstrates the versatility of the FAS1 domain in binding multiple ligands, which might be a conserved feature. The frequent assumption that FAS1 proteins are involved in "cell adhesion," however, is more context-dependent. It is derived from insightful experiments performed with animal cell cultures; however, it might be misleading for "hard-shelled" cells such as bacteria, fungi and plants that usually adhere to their ECM as a result of turgor pressure and build up adhesive materials such as pectin. By contrast, the designation of Tgfbi and Pn as matricellular proteins, defined as non-structural ECM-components that interact with cell surface receptors as mediators between the cell and its microenvironment [77,182], seems a more productive concept for approaching the common function of FAS1 proteins in all kingdoms of life including plants. The crucial challenge for future work on plant FAS1 proteins will be the identification of molecular interactors both of the FAS1 domain and of their abundant but enigmatic glycan modifications.

**Funding:** This research was funded by the Austrian Science Fund FWF (Grant number I1182-B22).

**Conflicts of Interest:** The author declares no conflict of interest.
