Bacterially synthesized vertebrate calmodulin is a specific substrate for ubiquitination.

Published

Journal Article

Calmodulin purified from bacteria which express a cloned chicken calmodulin gene can be selectively conjugated with ubiquitin, using enzymes present in reticulocyte extracts. Analyses of peptide products generated from limited proteolytic digestion of the calmodulin conjugate containing a single ubiquitin indicate that lysine 115 on calmodulin is the site of linkage. This linkage site is identical to that previously reported for calmodulin purified from Dictyostelium discoideum. Substrate-dependent ATP hydrolysis by a partially purified ubiquitin conjugation enzyme system from reticulocyte extracts was used to determine the enzyme affinity to calmodulin. Km values of 7 and 9 microM were determined for dictyostelium and the bacterially expressed calmodulin, respectively. The bacterially expressed calmodulin, unlike the Dictyostelium protein, can also form conjugates containing a 2-5 molar ratio of ubiquitin but at a slower rate than that observed for conjugation at lysine 115. Results from these studies further support our hypothesis that the post-translational methylation of lysine 115 found in most forms of calmodulin serves the important function of protecting calmodulin from ubiquitination and from degradation by the cytoplasmic ubiquitin-dependent proteolytic pathway. The capability of the bacterially expressed calmodulin to form conjugates with a high molar ratio of ubiquitin suggests that the post-translational acetylation of the N terminus of calmodulin may serve a similar function.

Full Text

Duke Authors

Cited Authors

  • Gregori, L; Marriott, D; Putkey, JA; Means, AR; Chau, V

Published Date

  • February 25, 1987

Published In

Volume / Issue

  • 262 / 6

Start / End Page

  • 2562 - 2567

PubMed ID

  • 3029086

Pubmed Central ID

  • 3029086

International Standard Serial Number (ISSN)

  • 0021-9258

Language

  • eng

Conference Location

  • United States