Disease relevance of GAP43

• Toward this end, it was demonstrated that recombinant neuromodulin purified from Escherichia coli and bovine neuromodulin were phosphorylated with similar Km values and stoichiometries and that protein kinase C mediated phosphorylation of both proteins abolished binding to calmodulin-Sepharose [1].
• Unlike the case for receptors, however, the GAP-43 effect is not blocked by pertussis toxin, nor affected by the presence or absence of beta gamma or of phospholipids [2].

Psychiatry related information on GAP43

• Motor activity at 30 days of age, but not at other ages, produced a unilateral reduction (-29.5%; p<0.001) in the level of GAP-43/B-50 endogenous phosphorylation in the contralateral striatum with respect to the ipsilateral side, while non-trained control animals did not show asymmetric differences [3].
• Here we confirm and extend this observation, describing that a one trial inhibitory avoidance learning was associated with rapid and specific increases in B-50/GAP-43 phosphorylation in vitro and in PKC activity in hippocampal synaptosomal membranes [4].

High impact information on GAP43

• GAP-43 is a neuronal protein that increases guanine nucleotide exchange by heterotrimeric G proteins [5].
• Two cysteine residues near the N-terminus of GAP-43 are subject to palmitoylation, and are necessary for membrane binding as well as for G(o) activation [5].
• This stimulatory effect of mastoparan was mimicked by GAP-43, an activator of the granule-associated Go, and specifically inhibited by antibodies against Galphao [6].
• These results suggest that the calmodulin-binding domain of GAP-43 is directly involved in the GAP-43-membrane interaction and undergoes a conformational change upon binding to phospholipid membranes [7].
• This provides structural confirmation for two binding modes and suggests that CaM regulates the biological activities of RC3 and GAP-43 through an allosteric, Ca(2+)-sensitive mechanism that can be uncoupled by protein kinase C-mediated phosphorylation [8].

Biological context of GAP43

• Phosphorylation by casein kinase II did not affect the ability of neuromodulin to bind to calmodulin-Sepharose [9].
• A comparison of the amino acid sequence of neurogranin with that of the brain-specific PKC substrate neuromodulin, revealed a strikingly conserved amino acid sequence AA(X)KIQA-SFRGH(X)(X)RKK(X)K [10].
• A mass spectrometric study on the in vivo posttranslational modification of GAP-43 [11].
• Neuromodulin (p57, GAP-43, F1, B-50) is a major neural-specific, calmodulin binding protein found in brain, spinal cord, and retina that is associated with membranes [12].
• We propose that the amino acid sequence shared by neurogranin and neuromodulin reflects a functional relationship between these two proteins and that the consensus sequence represents a conserved PKC phosphorylation site and a calmodulin binding domain that characterizes a class of brain-specific PKC substrates [10].

Anatomical context of GAP43

• GAP-43 is a neuronal protein associated with the cytosolic face of the growth cone plasma membrane and stimulates binding of guanosine 5'-3-O-(thio)triphosphate (GTP gamma S) to Go (Strittmatter, S. M., Valenzuela, D., Kennedy, T. E., Neer, E. J., and Fishman, M. C. (1990) Nature 344, 836-841) [2].
• Phosphorylation of the casein kinase II domain of B-50 (GAP-43) in rat cortical growth cones [13].
• Immunohistochemical studies using these carboxy-terminal antipeptide antibodies revealed a widespread distribution of GAP-43 immunoreactivity throughout the adult rat brain and spinal cord, in a pattern generally consistent with earlier histochemical studies [14].
• B50/neuromodulin is a neuronal phosphoprotein that is found in association with the inner membrane of nerve cells [15].

Associations of GAP43 with chemical compounds

• Characterization of the calmodulin binding domain of neuromodulin. Functional significance of serine 41 and phenylalanine 42 [16].
• The sensitivity of the neuromodulin/calmodulin binding interaction to negative charge at serine 41 was determined by substitution of serine 41 with an aspartate or an asparagine residue [16].
• There is specificity to the interaction, in that GAP-43 increases GTP gamma S binding to recombinant alpha o and alpha i1, but not to recombinant alpha s [2].
• A rapid purification method for neuromodulin was developed taking advantage of its newly discovered property, solubility in 2.5% perchloric acid, and of its previously recognized calmodulin-binding property [17].
• One of these phosphatases, which represented approximately 60% of the total neuromodulin phosphatase activity, was tentatively identified as calcineurin by its requirement for Ca2+ and calmodulin (CaM) and inhibition of its activity by chlorpromazine [12].

Other interactions of GAP43

• Dephosphorylation of neuromodulin by calcineurin [12].
• Phosphorylation reverses the membrane association of peptides that correspond to the basic domains of MARCKS and neuromodulin [18].

Analytical, diagnostic and therapeutic context of GAP43

• Recombinant neuromodulin was phosphorylated by using protein kinase C and [gamma-32P]ATP and digested with trypsin, and the resulting peptides were separated by HPLC [1].
• We examine RC3.CaM and GAP-43.CaM interactions by circular dichroism spectroscopy using purified, recombinant RC3 and GAP-43, sequence variants of RC3 displaying qualitative and quantitative differences in CaM binding affinities, and overlapping peptides that cumulatively span the entire amino acid sequence of RC3 [8].
• The titration of enzyme with increasing neuromodulin concentrations demonstrated a concentration-dependent decrease in enzyme activity [19].
• This contralateral change in GAP-43 phosphorylation correlated with the running speed developed by the animals [(r=0.9443, p=0.0046, n=6, relative to control group) and (r=0.8813, p=0.0203, n=6, with respect to the ipsilateral side of the exercised animals)] [3].
• Polyclonal antipeptide antibodies raised in rabbits were affinity purified and their specificity for GAP-43 tested by Western blotting [14].

References