Tissue-specific alternative splicing generates two synaptojanin isoforms with differential membrane binding properties.
Synaptojanin is an Src homology 3 domain-binding inositol 5-phosphatase that is thought to function in synaptic vesicle endocytosis. It is encoded by a cDNA with two open reading frames separated by an in-frame stop codon. The first open reading frame encodes a 145-kDa form of the protein, whereas a 170-kDa isoform appears to be composed of both open reading frames and contains additional Src homology 3 domain-binding consensus sequences. Here, we demonstrate that the two synaptojanin isoforms are generated by the alternative use of an exon containing the stop codon. Whereas the 145-kDa isoform is highly enriched in adult brain, the 170-kDa isoform is excluded from this tissue and has a widespread distribution in non-neuronal cells. Unlike the 145-kDa isoform, which can be removed from membranes by a low salt wash, the 170-kDa isoform remains membrane-associated, even in the presence of 1 salt. Further, the 170-kDa form, but not the 145-kDa form, can be isolated from membranes as part of a large molecular weight complex. These properties may allow the 170-kDa isoform of synaptojanin to play a unique and perhaps more general role in endocytosis as compared with the 145-kDa isoform.
Ramjaun
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AR
Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec H3A 2B4, Canada.
McPherson
P S
PS
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D001483:Base Sequence; D001921:Brain / Q000254:growth & development / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D018076:DNA, Complementary; D004705:Endocytosis; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D016716:PC12 Cells; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D011485:Protein Binding; D018909:src Homology Domains
D018076:DNA, Complementary; D009419:Nerve Tissue Proteins; C097702:synaptojanin; D010744:Phosphoric Monoester Hydrolases