Crystal and molecular structure of the sulfhydryl protease calotropin DI at 3·2 Å resolution

U. Heinemann, G. P. Pal, R. Hilgenfeld, W. Saenger*

*Corresponding author for this work
33 Citations (Scopus)


The three-dimensional structure of the sulfhydryl protease calotropin DI from the madar plant, Calotropis gigantea, has been determined at 3·2 Å resolution using the multiple isomorphous replacement method with five heavy atom derivatives. A Fourier synthesis based on protein phases with a mean figure of merit of 0·857 was used for model building. The polypeptide backbone of calotropin DI is folded to form two distinct lobes, one of which is comprised mainly of α-helices, while the other is characterized by a system of all antiparallel pleated sheets. The overall molecular architecture closely resembles those found in the sulfhydryl proteases papain and actinidin. Despite the unknown amino acid sequence of calotropin DI a number of residues around its active center could be identified. These amino acid side-chains were found in a similar arrangement as the corresponding ones in papain and actinidin. The polypeptide chain between residues 1 and 18 of calotropin DI folds in a unique manner, providing a possible explanation for the unusual inability of calotropin DI to hydrolyze those synthetic substrates that papain and actinidin act upon.

Original languageEnglish
JournalJournal of Molecular Biology
Issue number4
Pages (from-to)591-606
Number of pages16
Publication statusPublished - 15.11.1982

Research Areas and Centers

  • Academic Focus: Center for Infection and Inflammation Research (ZIEL)


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