Mtd (BPP-1 bacteriophage)

This part codes for the Major Tropism Determinant (Mtd) protein responsible for selective protein binding by the BPP-1 bacteriophage. In its native form, it has moderate affinity to the pertactin proteins expressed on the surface of Bordetella, the phage's natural host. The mtd gene has 22 specific nucleotides in its sequence that can be mutagenized to change the binding properties without adversely affecting the folding and stability of the protein. Mutations to these nucleotides give the Mtd protein the potential to bind to a very large range of target proteins. The mutagenic sites are highlighted below in red:

Mutagenic Sites on mtd gene.

In the natural phage system, libraries of mtd are created by the BPP-1 bacteriophage's Diversity Generating Retroelement. For in vitro library generation, synthetic methods such as PCR using variable oligonucleotides can be used.