Selective carboxyl methylation of structurally altered calmodulins in Xenopus oocytes

Journal Article · Wed Dec 05 04:00:00 EST 1990 · Journal of Biological Chemistry; (USA)

OSTI ID:6229580

Desrosiers, R R; Romanik, E A; O'Connor, C M ^[1]

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1. Worcester Foundation for Experimental Biology, Shrewsbury, MA (USA)

The eucaryotic protein carboxyl methyltransferase specifically modifies atypical D-aspartyl and L-isoaspartyl residues which are generated spontaneously as proteins age. The selectivity of the enzyme for altered proteins in intact cells was explored by co-injecting Xenopus laevis oocytes with S-adenosyl-L-(methyl-3H)methionine and structurally altered calmodulins generated during a 14-day preincubation in vitro. Control experiments indicated that the oocyte protein carboxyl methyltransferase was not saturated with endogenous substrates, since protein carboxyl methylation rates could be stimulated up to 8-fold by increasing concentrations of injected calmodulin. The oocyte protein carboxyl methyltransferase showed strong selectivities for bovine brain and bacterially synthesized calmodulins which had been preincubated in the presence of 1 mM EDTA relative to calmodulins which had been preincubated with 1 mM CaCl2. Radioactive methyl groups were incorporated into base-stable linkages with recombinant calmodulin as well as into carboxyl methyl esters following its microinjection into oocytes. This base-stable radioactivity most likely represents the trimethylation of lysine 115, a highly conserved post-translational modification which is present in bovine and Xenopus but not in bacterially synthesized calmodulin. Endogenous oocyte calmodulin incorporates radioactivity into both carboxyl methyl esters and into base-stable linkages following microinjection of oocytes with S-adenosyl-(methyl-3H)methionine alone. The rate of oocyte calmodulin carboxyl methylation in injected oocytes is calculated to be similar to that of lysine 115 trimethylation, suggesting that the rate of calmodulin carboxyl methylation is similar to that of calmodulin synthesis. At steady state, oocyte calmodulin contains approximately 0.0002 esters/mol of protein, which turn over rapidly.

• OSTI ID: 6229580
• Journal Information: Journal of Biological Chemistry; (USA), Journal Name: Journal of Biological Chemistry; (USA) Vol. 265:34; ISSN JBCHA; ISSN 0021-9258
• Country of Publication: United States
• Language: English

Related Subjects

550501* -- Metabolism-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ALKALINE EARTH METAL COMPOUNDS
AMINO ACIDS
AMPHIBIANS
ANIMALS
AQUATIC ORGANISMS
BACTERIA
BODY
BRAIN
CALCIUM CHLORIDES
CALCIUM COMPOUNDS
CALCIUM HALIDES
CALMODULIN
CARBOXYLIC ACIDS
CATTLE
CENTRAL NERVOUS SYSTEM
CHELATING AGENTS
CHEMICAL REACTIONS
CHLORIDES
CHLORINE COMPOUNDS
DOMESTIC ANIMALS
DRUGS
EDTA
ENZYMES
ESCHERICHIA COLI
FROGS
GERM CELLS
HALIDES
HALOGEN COMPOUNDS
HYDROGEN COMPOUNDS
ISOTOPE APPLICATIONS
LIPOTROPIC FACTORS
MAMMALS
METABOLISM
METHIONINE
METHYL TRANSFERASES
METHYLATION
MICROORGANISMS
NERVOUS SYSTEM
OOCYTES
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC SULFUR COMPOUNDS
ORGANS
POST-TRANSLATION MODIFICATION
PROTEINS
RUMINANTS
SPECIFICITY
TRACER TECHNIQUES
TRANSFERASES
TRITIUM COMPOUNDS
VERTEBRATES