A comparison of the structures of the alpha:beta and alpha:gamma dimers of mouse salivary androgen-binding protein (ABP) and their differential steroid binding.

Mouse salivary androgen-binding protein (ABP) is a family of dimeric proteins that may play a pheromonal role in Mus musculus. The protein dimer consists of a common alpha subunit disulfide-bonded to a variable (beta or gamma) subunit. Here we report N-terminal sequences of the beta and gamma subunits, showing that they are very similar to each other while being quite different from the alpha subunit. We demonstrate differential androgen binding by the two dimers. Both bind dihydrotestosterone to about the same extent but the alpha:beta dimer binds significantly more testosterone than the alpha:gamma dimer. We discuss the possible significance of this diversity of androgen binding with respect to the possibility that androgen binding is related to a putative pheromonal role for the protein.