| 633201 | Molecular characterization of light chain 3. A microtubule binding subunit of MAP1A and MAP1B. | Mann SS and Hammarback JA, J Biol Chem 1994 Apr 15;269(15):11492-7. | Light chain 3 (LC3) is a subunit of the neuronal microtubule-associated proteins (MAPs), MAP1A and MAP1B. Recent findings show that the cDNAs for MAP1A and MAP1B encode polyproteins that contain the MAP1A 700;'>MAP1A or MAP1B heavy chain and a LC2 or LC1 subunit, respectively. We have sequenced a cDNA encoding rat LC3, and its sequence is not found in the MAP1A/LC2 or MAP1B/LC1 polyprotein cDNAs. The deduced amino acid sequence of LC3 is highly conserved between rat and mouse. Rat LC3 is a 16.4-kDa protein with a predicted pI of 9.2. It is encoded on a 1.7-kilobase mRNA. Our anti-LC3 antiserum shows that LC3 is abundant only in neurons and that the majority of LC3 in brain co-purifies with microtubules. Purified recombinant rat LC3 retains the ability to associate with microtubules assembled in the presence of brain MAPs and with microtubules assembled from purified tubulin. We propose that LC3 functions primarily as a MAP1A and MAP1B subunit and that its expression could regulate the microtubule binding activity of MAP1A and MAP1B. | 7908909 | 1994-08-01 |
| 13432230 | The guanylate kinase domain of the MAGUK PSD-95 binds dynamically to a conserved motif in MAP1a. | Reese ML, etal., Nat Struct Mol Biol. 2007 Feb;14(2):155-63. Epub 2007 Jan 14. | The postsynaptic density protein PSD-95 and related membrane-associated guanylate kinases are scaffolding proteins, whose modular interaction motifs organize protein complexes at cell junctions. The signature guanylate kinase domain (GK) contains elements of the protein's GMP-binding site but does n ot bind nucleotide. Instead, the GK domain has evolved from an enzyme to a protein-protein interaction motif. Here, we show that this canonical GMP-binding region interacts with microtubule-associated protein-1a (MAP1a) and we present a structural model. We determine the consensus GK-binding sequence in MAP1a and demonstrate that PSD-95 can use a similar interaction mode to bind diverse protein partners. Furthermore, we show that PSD-95 GK has adopted the conformational flexibility of the ancestral enzyme to bind its varied ligands, which suggests a mechanism of regulation. | 17220895 | 2007-02-01 |
| 11251910 | Mutations in the microtubule-associated protein 1A (Map1a) gene cause Purkinje cell degeneration. | Liu Y, etal., J Neurosci. 2015 Mar 18;35(11):4587-98. doi: 10.1523/JNEUROSCI.2757-14.2015. | The structural microtubule-associated proteins (MAPs) are critical for the organization of neuronal microtubules (MTs). Microtubule-associated protein 1A (MAP1A) is one of the most abundantly expressed MAPs in the mammalian brain. However, its in vivo function r emains largely unknown. Here we describe a spontaneous mouse mutation, nm2719, which causes tremors, ataxia, and loss of cerebellar Purkinje neurons in aged homozygous mice. The nm2719 mutation disrupts the Map1a gene. We show that targeted deletion of mouse Map1a gene leads to similar neurodegenerative defects. Before neuron death, Map1a mutant Purkinje cells exhibited abnormal focal swellings of dendritic shafts and disruptions in axon initial segment (AIS) morphology. Furthermore, the MT network was reduced in the somatodendritic and AIS compartments, and both the heavy and light chains of MAP1B, another brain-enriched MAP, was aberrantly distributed in the soma and dendrites of mutant Purkinje cells. MAP1A has been reported to bind to the membrane-associated guanylate kinase (MAGUK) scaffolding proteins, as well as to MTs. Indeed, PSD-93, the MAGUK specifically enriched in Purkinje cells, was reduced in Map1a(-/-) Purkinje cells. These results demonstrate that MAP1A functions to maintain both the neuronal MT network and the level of PSD-93 in neurons of the mammalian brain. | 25788676 | 2015-06-01 |
| 2314804 | Exchange protein directly activated by cAMP (EPAC) interacts with the light chain (LC) 2 of MAP1A. | Magiera MM, etal., Biochem J. 2004 Sep 15;382(Pt 3):803-10. | Using EPAC1 (exchange protein directly activated by cAMP 1) as bait in two-hybrid screens of foetal and adult human brain libraries, we identified the LC2 (light chain 2) of MAP1A (microtubule-associated protein 1A) as a protein capable of interaction with EPAC1 . We applied an immunoprecipitation assay to demonstrate protein interaction between EPAC1 and LC2 in co-transfected human embryonic kidney 293 cells. EPAC2 also co-immunoprecipitated with LC2 from extracts of rat cerebellum. Immunolocalization in co-transfected human embryonic kidney 293 cells revealed that EPAC1 co-localizes with LC2 throughout the cell body. We found that endogenous EPAC2 is also immunolocalized with LC2 in PC12 cells. Immunolocalization of EPAC1 in transfected COS1 cells showed that EPAC1 is associated with the perinuclear region surrounding the nucleus and filamentous structures throughout the cell. Removal of the cAMP-binding domain of EPAC1 (DeltacAMP-EPAC1) appeared to disrupt targeting of EPAC1 in cells resulting in a more dispersed staining pattern. Using two-hybrid assay, we tested the ability of LC2 to interact with DeltacAMP-EPAC1 and DeltaDEP-EPAC1, which lacks a DEP domain (dishevelled, Egl-10 and pleckstrin homology domain). We found that deletion of the cAMP-binding domain inhibited interaction between EPAC1 and LC2 in a two-hybrid assay, but removal of the DEP domain had little effect. LC2 was found to interact with a glutathione-S-transferase-fusion protein of the cAMP-binding domain of EPAC1 in a pull-down assay, but not the DEP, REM (Ras exchange motif) or CAT (catalytic) domains. Together with our two-hybrid results, this suggests that the cAMP-binding domain of EPAC1 mediates interaction with LC2. | 15202935 | 2004-11-01 |
| 155230745 | Caldendrin but not calmodulin binds to light chain 3 of MAP1A/B: an association with the microtubule cytoskeleton highlighting exclusive binding partners for neuronal Ca(2+)-sensor proteins. | Seidenbecher CI, etal., J Mol Biol. 2004 Feb 27;336(4):957-70. doi: 10.1016/j.jmb.2003.12.054. | Caldendrin is a neuronal Ca(2+)-sensor protein (NCS), which represents the closest homologue of calmodulin (CaM) in nerve cells. It is tightly associated with the somato-dendritic cytoskeleton of neurons and highly enriched in the postsynaptic cytomatrix. Here, we report that caldendrin specifically associates with the microtubule cytoskeleton via an interaction with light chain 3 (LC3), a microtubule component with sequence homology to the GABAA receptor-associated protein (GABARAP), which is, like LC3, probably involved in cellular transport processes. Interestingly, two binding sites exist in LC3 for caldendrin from which only one exhibits a strict Ca(2+)-dependency for the interaction to take place but both require the presence of the first two EF-hands of caldendrin. CaM, however, is not capable of binding to LC3 at both sites despite its high degree of primary structure similarity with caldendrin. Computer modelling suggests that this might be explained by an altered distribution of surface charges at the first two EF-hands rendering each molecule, in principle, specific for a discrete set of binding partners. These findings provide molecular evidence that NCS can transduce signals to a specific target interaction irrespective of Ca(2+)-concentrations and CaM-levels. | 15095872 | 2004-02-27 |
| 10059665 | Interaction of casein kinase 1 delta (CK1 delta) with the light chain LC2 of microtubule associated protein 1A (MAP1A). | Wolff S, etal., Biochim Biophys Acta. 2005 Sep 10;1745(2):196-206. | CK1delta, a member of the casein kinase 1 family of serine/threonine specific kinases, has been shown to be involved in the regulation of microtubule dynamics. We have now identified a 176 aa fragment of the light chain LC2 of MAP1A (termed LC2-P16) specificall y interacting with CK1delta. Two CK1delta interacting domains of LC2 were identified, located between aa 2629 and 2753 close to aa 2683 and between aa 2712 and 2805 of LC2. The two regions necessary for the interaction of LC2 with CK1delta have been mapped between aa 76-103 and aa 351-375 of CK1delta. Furthermore, LC2 has been identified as a new substrate of CK1delta. We therefore propose a model in which CK1delta could modulate microtubule dynamics by changing the phosphorylation status of the light chain LC2 of MAP1A. | 15961172 | 2005-08-01 |
| 71122 | Microtubule-associated protein 1A (MAP1A) and MAP1B: light chains determine distinct functional properties. | Noiges R, etal., J Neurosci 2002 Mar 15;22(6):2106-14. | The microtubule-associated proteins 1A (MAP1A) and 1B (MAP1B) are distantly related protein complexes consisting of heavy and light chains and are thought to play a role in regulating the neuronal cytoskeleton, MAP1B during neuritogenesis and MAP1A eight:700;'>MAP1A in mature neurons. To elucidate functional differences between MAP1B and MAP1A and to determine the role of the light chain in the MAP1A protein complex, we chose to investigate the functional properties of the light chain of MAP1A (LC2) and compare them with the light chain of MAP1B (LC1). We found that LC2 binds to microtubules in vivo and in vitro and induces rapid polymerization of tubulin. A microtubule-binding domain in its NH(2) terminus was found to be necessary and sufficient for these activities. The analysis of LC1 revealed that it too bound to microtubules and induced tubulin polymerization via a crucial but structurally unrelated NH(2)-terminal domain. The two light chains differed, however, in their effects on microtubule bundling and stability in vivo. Furthermore, we identified actin filament binding domains located at the COOH terminus of LC2 and LC1 and obtained evidence that binding to actin filaments is attributable to direct interaction with actin. Our findings establish LC2 as a crucial determinant of MAP1A function, reveal LC2 as a potential linker of neuronal microtubules and microfilaments, and suggest that the postnatal substitution of MAP1B by MAP1A leads to expression of a protein with an overlapping but distinct set of functions. | 11896150 | 2002-07-01 |
| 405650353 | The role of MAP1A light chain 2 in synaptic surface retention of Cav2.2 channels in hippocampal neurons. | Leenders AG, etal., J Neurosci. 2008 Oct 29;28(44):11333-46. doi: 10.1523/JNEUROSCI.3078-08.2008. | Ca(v)2.2 channels are localized at nerve terminals where they play a critical role in neurotransmission. However, the determinant that controls surface retention of these channels has not been identified. Here, we report that presynaptic surface localization of Ca(v)2.2 is mediated through its inter action with light chain 2 (LC2) of microtubule-associated protein MAP1A. Deletion of a 23-residue binding domain within the Ca(v)2.2 C terminus resulted in reduced synaptic distribution of the mutant channels. Using an antibody generated against an extracellular epitope of Ca(v)2.2, we demonstrate that interfering the interaction with LC2 reduced surface expression of endogenous Ca(v)2.2 at presynaptic boutons. In addition, the disruption of LC2-Ca(v)2.2 coupling reduced Ca(2+)-influx into nerve terminals through Ca(v)2.2 and impaired activity-dependent FM4-64 uptake. The treatments of neurons with Latrunculin A to disrupt actin filaments resulted in reduced density of surface Ca(v)2.2-positive boutons. Furthermore, LC2NT, a LC2 truncated mutant lacking the actin-binding domain, could not rescue Ca(v)2.2 surface expression after suppressing LC2 expression with RNAi. Because actin filaments are major cytomatric components at the presynaptic boutons, these observations suggest a mechanism by which LC2 provides anchoring of surface Ca(v)2.2 to the actin cytoskeleton, thus contributing to presynaptic function. | 18971475 | 2008-10-29 |
