Fibronectin type III domains are found in many different proteins including cell
surface receptors and cell adhesion molecules. The crystal structure of one such
domain from the extracellular matrix protein tenascin was determined. The
structure was solved by multiwavelength anomalous diffraction (MAD) phasing of
the selenomethionyl protein and has been refined to 1.8 angstrom resolution. The
folding topology of this domain is identical to that of the extracellular
domains of the human growth hormone receptor, the second domain of CD4, and
PapD. Although distinct, this topology is similar to that of immunoglobulin
constant domains. An Arg-Gly-Asp (RGD) sequence that can function for cell
adhesion is found in a tight turn on an exposed loop.
