View metadata, citation and similar papers at core.ac.uk brought to you by CORE Researchprovided Article by Elsevier1193 - Publisher Connector The prosequence of procaricain forms an a-helical domain that prevents access to the substrate-binding cleft Matthew R Groves, Mark AJ Taylor, Mandy Scott, Nicola J Cummings Richard W Pickersgill* and John A Jenkins* Background: Cysteine proteases are involved in a variety of cellular processes Address: Department of Food Macromolecular including cartilage degradation in arthritis, the progression of Alzheimer’s Science, Institute of Food Research, Earley Gate, disease and cancer invasion: these enzymes are therefore of immense biological Whiteknights Road, Reading, RG6 6BZ, UK. importance. Caricain is the most basic of the cysteine proteases found in the *Corresponding authors. latex of Carica papaya. It is a member of the papain superfamily and is E-mail:
[email protected] homologous to other plant and animal cysteine proteases. Caricain is naturally
[email protected] expressed as an inactive zymogen called procaricain. The inactive form of the Key words: caricain, cysteine protease, density protease contains an inhibitory proregion which consists of an additional 106 modification, X-ray structure, zymogen N-terminal amino acids; the proregion is removed upon activation. Received: 25 June 1996 Results: The crystal structure of procaricain has been refined to 3.2 Å Revisions requested: 23 July 1996 Revisions received: 12 August 1996 resolution; the final model consists of three non-crystallographically related Accepted: 28 August 1996 molecules. The proregion of caricain forms a separate globular domain which binds to the C-terminal domain of mature caricain.