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J Biol Chem. 2017 Feb 24;292(8):3506-3516. doi: 10.1074/jbc.M116.768077. Epub 2017 Jan 18.

Intramembrane Proteolysis of Astrotactins.

Author information

1
From the Departments of Molecular Biology and Genetics.
2
From the Departments of Molecular Biology and Genetics, jnathans@jhmi.edu.
3
Neuroscience, and.
4
Ophthalmology, Howard Hughes Medical Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.

Abstract

Astrotactins are vertebrate-specific membrane proteins implicated in neuron-glia interactions during central nervous system development and in hair follicle polarity during skin development. By studying epitope-tagged derivatives of mouse astrotactin-2 (Astn2) produced in transfected cells, we determined that the amino and carboxyl termini reside in the extracellular space and are initially linked by two transmembrane segments and a single cytoplasmic domain. We further show that Astn2 undergoes proteolytic cleavage in the second transmembrane domain (TM2) and that a disulfide bond holds the resulting two fragments together. Recombinant Astn1 also undergoes TM2 cleavage, as does Astn2 isolated from mouse cerebellum. Astn2 intramembrane proteolysis is insensitive to replacement of TM2 by the transmembrane domain of CD74 or by 21 alanines. However, replacement of TM2 by the transmembrane domain of CD4, the asialoglycoprotein receptor, or the transferrin receptor eliminates intramembrane proteolysis, as does leucine substitution of residues that overlap or are immediately upstream of the cleavage site. Replacement of the transmembrane domain of CD74 or the asialoglycoprotein receptor with Astn2 TM2 leads to the appearance of a carboxyl-terminal fragment consistent with intramembrane proteolysis. These experiments define a highly unusual transmembrane topology for the astrotactins, reveal intramembrane proteolysis as a feature of astrotactin maturation, and constrain the substrate sequences that are permissive for cleavage of one type 2 transmembrane segment.

KEYWORDS:

intramembrane proteolysis; membrane protein; protein processing; protein sequence; transmembrane domain

PMID:
28100779
PMCID:
PMC5336181
DOI:
10.1074/jbc.M116.768077
[Indexed for MEDLINE]
Free PMC Article

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