Zhang, M., MacDonald, A. I., Hoyt, M. A. and Coffino, P. (2004) Proteasomes begin ornithine decarboxylase digestion at the C terminus. Journal of Biological Chemistry, 279(20), pp. 20959-20965. (doi: 10.1074/jbc.M314043200) (PMID:15016805)
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Abstract
Proteasomes denature folded protein substrates and thread them through a narrow pore that leads to the sequestered sites of proteolysis. Whether a protein substrate initiates insertion from its N or C terminus or in a random orientation has not been determined for any natural substrate. We used the labile enzyme ornithine decarboxylase (ODC), which is recognized by the proteasome via a 37-residue C-terminal tag, to answer this question. Three independent approaches were used to assess orientation as follows. 1) The 461-residue ODC protein chain was interrupted at position 305. The C-terminal fragment was degraded by purified proteasomes, but because processivity requires continuity of the polypeptide chain, the N-terminal fragment was spared. 2) A proteasome-inhibitory viral sequence prevented degradation when introduced near the C terminus but not when inserted elsewhere in ODC. 3) A bulky tightly folded protein obstructed in vivo degradation most effectively when positioned near the C terminus. These data demonstrate that the proteasome initiates degradation of this native substrate at the C terminus. The co-localization of entry site and degradation tag to the ODC C terminus suggests that recognition tags determine the site for initiating entry. Flexibility of a polypeptide terminus may promote the initiation of degradation.
Item Type: | Articles |
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Status: | Published |
Refereed: | Yes |
Glasgow Author(s) Enlighten ID: | MacDonald, Dr Alasdair |
Authors: | Zhang, M., MacDonald, A. I., Hoyt, M. A., and Coffino, P. |
College/School: | College of Medical Veterinary and Life Sciences > School of Infection & Immunity |
Journal Name: | Journal of Biological Chemistry |
Publisher: | American Society for Biochemistry and Molecular Biology |
ISSN: | 0021-9258 |
ISSN (Online): | 1083-351X |
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