Maltose-binding protein （MBP） is a part of the maltose/maltodextrin system of Escherichia coli, which is responsible for the uptake and efficient catabolism of maltodextrins. It is a complex regulatory and transport system involving many proteins and protein complexes. MBP has an approximate molecular mass of 42.5 kilodaltons. MBP is used to increase the solubility of recombinant proteins expressed in E. coli. The fusion of proteins with MBP usually enhances their solubility and facilitates their proper folding. In addition, such fusions can facilitate the crystallization of difficult proteins, e.g. membrane proteins. MBP can itself be used as an affinity tag for purification of recombinant proteins.