From Proteopedia
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Bovine Pancreatic Trypsin Inhibitor (BPTI) Mutant with Altered Binding Loop Sequence
BPTI is a single chain polypeptide with 58 amino acids. It's secondary structure includes one and . The beta sheet consists of (Ile18 to Asn 24 and Leu 29 to Tyr 35) with a consisting of four residues (Ala 25, Lys 26, Ala 27, Gly 28). Alpha helix
is 4 residues (Asp 3 to Cys 6), and is 8 residues (Ala 48 to Cys 55). There are three intrachain disulfide bonds in this polypeptide, one between , one between , and one between . These are important for BPTI's stability and its ability to withstand the harsh conditions of the digestive system. This protein has a (gray) with polar and charged residues (purple) extending mostly on the . The N-terminus and C-terminus are in contact through a salt bridge.
BPTI interacts with 98 as well as 4 . Ligand binds the protein through hydrophobic interactions between Glu 7, Lys 7, and Phe 41, as well as through 3 hydrogen bonds to Arg 42. Three water molecules are also interact with this ligand. Ligand has hydrophobic interaction with Ala 40, two hydrogen bonds with Arg 20, and one hydrogen bond with Tyr 35. Ligand
has hydrophobic interaction with Pro 2 and one hydrogen bond with Arg 1. Ligand has hydrophobic interaction with Cys 14.
This particular mutant of BPTI contains several residue substitutions within these loop, including a substitution at , which is is normally Lys but has been replaced by Arg.
