Structure of rat procathepsin B: model for inhibition of cysteine protease activity by the proregion

Background: Cysteine proteases of the papain superfamily are synthesized as inactive precursors with a 60–110 residue N-terminal prosegment. The propeptides are potent inhibitors of their parent proteases. Although the proregion binding mode has been elucidated for all other protease classes, that o...

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Bibliographic Details
Published in:Structure (London) 1996-04, Vol.4 (4), p.405-416
Main Authors: Cygler, Miroslaw, Sivaraman, J, Grochulski, Pawel, Coulombe, René, Storer, Andrew C, Mort, John S
Format: Article
Language:English
Subjects:
Animals
Binding Sites
cathepsin B
Cathepsin B - chemistry
Cathepsin B - genetics
Cathepsin B - metabolism
Crystallography, X-Ray
cysteine protease
Cysteine Proteinase Inhibitors - chemistry
Cysteine Proteinase Inhibitors - metabolism
Enzyme Activation
Enzyme Precursors - chemistry
Enzyme Precursors - genetics
Enzyme Precursors - metabolism
Leucine - analogs & derivatives
Leucine - chemistry
Leucine - metabolism
Models, Molecular
procathepsin B
proenzyme
Protein Conformation
Rats
Recombinant Proteins - chemistry
Recombinant Proteins - genetics
Recombinant Proteins - metabolism
Substrate Specificity
three-dimensional structure
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Summary:Background: Cysteine proteases of the papain superfamily are synthesized as inactive precursors with a 60–110 residue N-terminal prosegment. The propeptides are potent inhibitors of their parent proteases. Although the proregion binding mode has been elucidated for all other protease classes, that of the cysteine proteases remained elusive. Results We report the three-dimensional structure of rat procathepsin B, determined at 2.8 å resolution. The 62-residue proregion does not form a globular structure on its own, but folds along the surface of mature cathepsin B. The N-terminal part of the proregion packs against a surface loop, with Trp24p (p indicating the proregion) playing a pivotal role in these interactions. Inhibition occurs by blocking access to the active site: part of the proregion enters the substrate-binding cleft in a similar manner to a natural substrate, but in a reverse orientation. Conclusion The structure of procathepsin B provides the first insight into the mode of interaction between a mature cysteine protease from the papain superfamily and its prosegment. Maturation results in only one loop of cathepsin B changing conformation significantly, replacing contacts lost by removal of the prosegment. Contrary to many other proproteases, no rearrangement of the N terminus occurs following activation. Binding of the prosegment involves interactions with regions of the enzyme remote from the substrate-binding cleft and suggests a novel strategy for inhibitor design. The region of the prosegment where the activating cleavage occurs makes little contact with the enzyme, leading to speculation on the activation mechanism.
ISSN:0969-2126
1878-4186
DOI:10.1016/S0969-2126(96)00046-9