Disease relevance of calA

• Support for this comes from recent studies showing inhibition of protein synthesis by calmodulin antagonists in Ehrlich ascites tumor cells (Kumar, R. V., Panniers, R., Wolfman, A., and Henshaw, E.C. (1991) Eur. J. Biochem. 195, 313-319) [1].
• The use of [35S]calmodulin, labeled during its expression (VU-1-CaM) in Escherichia coli, visualized over 25 CaMBPs in Dictyostelium discoideum [2].

High impact information on calA

• Earlier studies had demonstrated that contractile vacuole membranes in Dictyostelium are extremely rich in calmodulin (Zhu, Q., and M. Clarke, 1992, J. Cell Biol. 118: 347-358) [3].
• This protein, termed MlcB, contains two EF-hand motifs and shares approximately 30% sequence identity with the N- and C-terminal lobes of calmodulin [4].
• In binding assays with immobilized calmodulin, arachidonic acid inhibited binding of calcineurin to calmodulin [5].
• Immunofluorescence analysis indicates that PAT1 colocalizes with bound calmodulin to intracellular membranes, probably components of the contractile vacuole complex [6].
• However, PAT1 lacks the highly conserved calmodulin-binding domain present in the C-terminal region of most plasma membrane Ca2+ ATPase-type enzymes [6].

Biological context of calA

• Purified calmodulin N-methyltransferase was incubated with extracts of rat tissues, and [methyl-3H]AdoMet and methylated proteins were resolved by electrophoresis in an attempt to discover substances other than calmodulin, but this enzyme only catalyzed the methylation of calmodulin, indicating a high degree of substrate specificity [7].
• The distribution, properties, and substrate specificity of S-adenosylmethionine:calmodulin (lysine) N-methyltransferse (EC 2.1.1.60, calmodulin N-methyltransferase) of the rat have been studied [7].
• Substrate-dependent ATP hydrolysis by a partially purified ubiquitin conjugation enzyme system from reticulocyte extracts was used to determine the enzyme affinity to calmodulin [8].
• 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 [8].
• Calmodulin activity is required for both cell fusion and pronuclear fusion [9].

Anatomical context of calA

• The endogenous 22-kDa calmodulin-binding activity was associated with ribosomes [1].
• Calmodulin N-methyltransferase was purified 470-fold with a 33% yield from rat testis cytosol, using ammonium sulfate precipitation and chromatography on DEAE-cellulose, CM-Sepharose, and Sephadex G-100 [7].
• Dictyostelium calmodulin also activated erythrocyte (Ca2+ + Mg2+)-ATPase and interacted with the inhibitory subunit of skeletal muscle troponin [10].
• Antibodies specific for Dictyostelium calmodulin were used in the present study to immunolocalize the contractile vacuole complex in relation to the Golgi complex (detected with wheat germ agglutinin) and the microtubule organizing center (MTOC, detected with anti-tubulin antibodies) [11].
• Despite this difference in localization, it is possible that vacuole-associated calmodulin in Dictyostelium cells and spindle-associated calmodulin in larger eukaryotic cells might perform a similar function, namely, regulating calcium levels [11].

Associations of calA with chemical compounds

• Dictyostelium calmodulin had one-third the specific activity of brain calmodulin in the Ca2+-dependent activation of brain cyclic nucleotide phosphodiesterase; this activation was inhibited for both proteins by 25 microM trifluoperazine [10].
• Three moles of methyl/mol of calmodulin were incorporated into lysine 115 of des(methyl)calmodulin, resulting in the formation of 1 mol of trimethyllysine at the site normally methylated in calmodulins from most species [7].
• Most interesting is the lack of trimethyllysine in Dictyostelium calmodulin [10].
• 5. The activity of the enzyme is not significantly altered by the presence of Ca2+, Ca2+ and calmodulin, EGTA, cAMP, or cGMP [12].
• Analyses of the cyanogen bromide fragments of the protein conjugate indicate that lysine 115 on calmodulin is the ubiquitin conjugation site [13].

Other interactions of calA

• Moreover, unlike calmodulin and CAF-1 expression, CBP1 mRNA is expressed preferentially during the multicellular stages of development [14].
• 3. By the addition of calmodulin, the inhibition of myosin heavy-chain phosphorylation was further enhanced [15].
• These two compounds as well as another Ca++ antagonist, 8-N,N-diethylamino)octyl-3,4,5-trimethoxy-benzoate (TMB-8) and a calmodulin inhibitor, N-(6-amino-hexyl)-5-chloro-1-naphthalene sulfonamide (W7), all specifically decrease cAMP-mediated prespore mRNA accumulation in a dose-dependent manner [16].
• Sequence analysis of the MyoD light chain showed it to be a unique protein, termed MlcD, that shares 44% sequence identity with Dictyostelium calmodulin and 43% sequence identity with Acanthamoeba castellanii myosin IC light chain [17].

Analytical, diagnostic and therapeutic context of calA

• We report the isolation and sequence determination of a cDNA containing most of the coding sequence for Dictyostelium discoideum calmodulin [18].
• Probing of Dictyostelium discoideum cell extracts after SDS-PAGE using (35)S-recombinant calmodulin (CaM) as a probe has revealed approximately three-dozen Ca(2+)-dependent calmodulin binding proteins [19].
• Chemical synthesis and expression of a calmodulin gene designed for site-specific mutagenesis [20].
• Isolation of homogeneous Dictyostelium CaM was accomplished in high yield by ion-exchange chromatography and Ca2+-dependent affinity chromatography on phenothiazine-Sepharose 4B [21].
• Purified CaM was used to raise high-affinity polyclonal antibodies suitable for immunoblotting, immunofluorescence, and immunoprecipitation experiments [22].

References