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 protei ns that may play a pheromonal role in Mus musculus. The protein dimer consi sts 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 subuni ts, showing that they are very similar to each other while being quite diff erent from the alpha subunit. We demonstrate differential androgen binding by the two dimers. Both bind dihydrotestosterone to about the same extent b ut the alpha:beta dimer binds significantly more testosterone than the alph a:gamma dimer. We discuss the possible significance of this diversity of an drogen binding with respect to the possibility that androgen binding is rel ated to a putative pheromonal role for the protein.