Maltose-binding protein
0Maltose-binding protein, by Wikipedia https://en.wikipedia.org/wiki?curid=10035262 / CC BY SA 3.0
#Proteins
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 encoded by the malE gene of Escherichia coli.
The malE gene codes for a precursor polypeptide （396 amino acid residues） which yields the mature MBP （370 residues） upon cleavage of the NH2-terminal extension （26 residues）.
The precursor and mature forms of MBP do not contain any cysteine residues.
MBP is a monomeric protein.
Crystal structures have shown that MBP is divided into two distinct globular domains that are connected by three short polypeptide segments.
The two domains are separated by a deep groove that contains the maltose/maltodextrin binding site.
Comparison of the structures of the liganded and unliganded forms of MBP has shown that the binding of maltose induces a major conformational change that closes the groove by a rigid motion of the two domains around the linking polypeptide hinge.
Both precursor and mature forms of MBP are functional for the binding of maltose.
The NH2-terminal extension decreases the folding rate of the precursor form of MBP relative to its mature form by at least 5 fold, but it has no effect on the unfolding rate.
The equilibrium unfolding of MBP can be modelled by a two-state mechanism with a stability ∆G（H2O） equal to 9.
45 kcal mol−1 at 25 °C, pH 7.
6.
MBP is exported into the periplasmic space of E. coli.
The NH2-terminal extension of MBP, also termed signal peptide, has two roles: （i） it slows down folding of the newly synthesized polypeptide, and （ii） it directs this polypeptide to the membrane and SecYEG translocon.
Once folded, the precursor can no longer enter the translocation p...
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