A Second Binding Site Revealed by C-Terminal Truncation of Calpain Small Subunit, a Penta-EF-Hand Protein

E. K. Leinala, J. S.C. Arthur, P. Grochulski, P. L. Davies, J. S. Elce, Z. Jia (Lead / Corresponding author)

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    6 Citations (Scopus)

    Abstract

    The subunits in calpain and in the related penta-EF-hand (PEF) proteins are bound through contacts between the unpaired EF-hand 5 from each subunit. To study subunit binding further, a tetra-EF-hand 18 kDa N- and C-terminally truncated form of the calpain small subunit was prepared (18k). This protein does not combine with the calpain large subunit to form active calpain, but forms homodimers in solution, as shown by ultracentrifugation. The X-ray structure of the 18k protein in the presence of cadmium was solved to a resolution of 2.0 Å. The structure of the monomer is almost identical to the known structure of the calpain small subunit, but the 18k protein forms an oligomer in the crystal by the use of two binding sites. One of these sites is an artefact arising from the C-terminal truncation, but the other is a naturally occurring site that is fully exposed to water in intact purified calpain. The characteristics of this site suggest that it may be important in binding other protein modulators involved in the regulation of calpain and of PEF proteins.

    Original languageEnglish
    Pages (from-to)649-655
    Number of pages7
    JournalProteins: Structure, Function and Genetics
    Volume53
    Issue number3
    DOIs
    Publication statusPublished - 15 Nov 2003

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