Characterization of monomeric and dimeric B domain of Staphylococcal protein A

Both monomeric and dimeric constructs of the B domain of protein A from Sta phylococcus aureus have been characterized by NMR, CD and fluorescence spec troscopy. The monomeric form of the protein was synthesized using a novel m ethod incorporating the use of a recombinant, folded, chimeric protein. A c omparison of the recombinant monomeric form with the commercially available dimeric form indicates that, although the dimer retains the integrity of t he three-helix bundle structure present in the monomer, there are interdoma in contacts in the dimeric form. A single long-lived water molecule in the hydrophobic core of the three-helix bundle of monomeric protein A may repre sent an important stabilizing factor for the three-helix bundle topology.