Novel SCAMPs lacking NPF repeats: ubiquitous and synaptic vesicle-specific forms implicate SCAMPs in multiple membrane-trafficking functions

J Neurosci. 2000 Nov 1;20(21):7941-50. doi: 10.1523/JNEUROSCI.20-21-07941.2000.

Abstract

In vertebrates, secretory carrier membrane proteins (SCAMPs) 1-3 constitute a family of putative membrane-trafficking proteins composed of cytoplasmic N-terminal sequences with NPF repeats, four central transmembrane regions (TMRs), and a cytoplasmic tail. SCAMPs probably function in endocytosis by recruiting EH-domain proteins to the N-terminal NPF repeats but may have additional functions mediated by their other sequences. We now demonstrate that SCAMPs form a much larger and more heterogeneous protein family than envisioned previously, with an evolutionary conservation extending to invertebrates and plants. Two novel vertebrate SCAMPs (SCAMPs 4 and 5), single SCAMP genes in Caenorhabditis elegans and Drosophila melanogaster, and multiple SCAMPs in Arabidopsis thaliana were identified. Interestingly, the novel SCAMPs 4 and 5 lack the N-terminal NPF repeats that are highly conserved in all other SCAMPs. RNA and Western blotting experiments showed that SCAMPs 1-4 are ubiquitously coexpressed, whereas SCAMP 5 is only detectable in brain where it is expressed late in development coincident with the elaboration of mature synapses. Immunocytochemistry revealed that SCAMP 5 exhibits a synaptic localization, and subcellular fractionations demonstrated that SCAMP 5 is highly enriched in synaptic vesicles. Our studies characterize SCAMPs as a heterogeneous family of putative trafficking proteins composed of three isoforms that are primarily synthesized outside of neurons (SCAMPs 2-4), one isoform that is ubiquitously expressed but highly concentrated on synaptic vesicles (SCAMP 1), and one brain-specific isoform primarily localized to synaptic vesicles (SCAMP 5). The conservation of the TMRs in all SCAMPs with the variable presence of N-terminal NPF repeats suggests that in addition to the role of some SCAMPs in endocytosis mediated by their NPF repeats, all SCAMPs perform a "core" function in membrane traffic mediated by their TMRs.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Biological Transport / genetics
  • COS Cells
  • Caenorhabditis elegans / genetics
  • Carrier Proteins / genetics*
  • Carrier Proteins / metabolism*
  • Drosophila melanogaster / genetics
  • Expressed Sequence Tags
  • Intracellular Membranes / metabolism*
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism
  • Mice
  • Molecular Sequence Data
  • Multigene Family / genetics
  • Organ Specificity / genetics
  • Peas / genetics
  • Protein Isoforms / genetics
  • Protein Isoforms / metabolism
  • RNA, Messenger / analysis
  • Rats
  • Repetitive Sequences, Amino Acid / genetics*
  • Sequence Alignment
  • Sequence Homology, Amino Acid
  • Synaptic Vesicles / metabolism*
  • Synaptosomes / metabolism
  • Transfection
  • Vesicular Transport Proteins

Substances

  • Carrier Proteins
  • Membrane Proteins
  • Protein Isoforms
  • RNA, Messenger
  • Scamp1 protein, mouse
  • Vesicular Transport Proteins

Associated data

  • GENBANK/AF240784
  • GENBANK/AF241833
  • GENBANK/AF241834
  • GENBANK/AF295102
  • GENBANK/AF295402
  • GENBANK/AF295403
  • GENBANK/AF295404
  • GENBANK/AF295405