MaltoseBinding

Maltose-binding protein (MBP), also known as MalE, is a periplasmic binding protein of the maltose/maltodextrin transport system in Escherichia coli and other Gram-negative bacteria. It captures maltose and related oligosaccharides in the periplasm and delivers them to the MalFGK2 transporter for uptake into the cytoplasm. MBP has high affinity for maltose and maltodextrins and undergoes a ligand-induced conformational change from an open to a closed state, which facilitates interaction with the transport complex.

Structurally, mature MBP is about 40 to 43 kDa and comprises two lobes connected by a flexible hinge. The N-terminal signal peptide directs export to the Sec pathway, and the mature protein resides in the periplasm without transmembrane segments. The two-domain architecture supports large conformational changes upon ligand binding, contributing to its role in transporter recognition.

In biotechnology, MBP is widely used as an expression fusion partner to improve solubility and folding of recombinant proteins in E. coli. MBP fusions are commonly purified on amylose resin via the MBP–amylose interaction. The tag can enhance solubility and aid proper folding; it is typically removed by proteolysis using site-specific proteases such as Factor Xa or TEV protease to yield the target protein.

Limitations include the relatively large size of MBP, which can affect the behavior or activity of the fused protein, and the need for an additional cleavage step to remove the tag in downstream applications. Beyond expression, MBP is also employed as a crystallization chaperone in structural biology to stabilize challenging proteins for structural analysis.