A mosaic protein is one that is composed of more than one functional domain. A typical example of a mosaic protein can be seen in tissue plasminogen activator (tPA) (Fig. 1). tPA contains at least four functional domains; an epidermal growth factor-like domain (EGF motif), two Kringle domains, and a serine proteinase domain. These DNA segments coding for these domains are believed to have been collected together into a single gene by either domain shuffling or exon shuffling during evolution.
Figure 1. The domain structures of a number of related mosaic proteins. Kringle domains are indicated by "K" and schematically, (F—finger motif; C:—Ca++ binding domain; P—serine protease domain; G—EGF motif; uPA— urokinase; tPA—tissue plasminogen activator).
Most proteins possess more than one functional domain and can be considered mosaic proteins (Fig. 1). Each such domain usually carries its own function, so a mosaic protein can be considered to be a multifunctional protein. Consequently, mosaic proteins are evolutionarily important, because they can create diverse functions of proteins. For more detail, see Exon Shufflingand Domain Shuffling.
