Maltose-binding protein (MBP), a member of the periplasmic binding protein family of Gram negative bacteria, is a versatile substrate for protein engineering. In common with other periplasmic proteins, it is extremely protease resistant, and it can fold properly in both the cytoplasmic and periplasmic compartments. It binds a variety of glucose-14-glucose polysaccharides, from maltose and longer chain maltodextrins to -cyclodextrin. Upon binding its ligand, it undergoes a large conformational change. These properties have made MBP attractive for a number of engineering studies that have elucidated its role in maltodextrin transport, tuned its properties as an affinity and solubility tag, and transformed it into an allosteric effector or a biosensor for both its natural ligand and for compounds as varied as zinc and TNT (Marvin & Hellinga, 2001, Naal et al., 2002, Wu et al., 1997).