Identification of an Evolutionarily Conserved Heterotrimeric Protein Complex Involved in Protein Targeting

doi:10.1074/jbc.273.48.31633

Identification of an Evolutionarily Conserved Heterotrimeric Protein Complex Involved in Protein Targeting*

From the ^‡Howard Hughes Medical Institute,^§Department of Internal Medicine and ^‖Biological Chemistry, the ^**Department of Neurology, University of Michigan Medical Center, Ann Arbor, Michigan 48109, and Veterans Affairs Medical Center GRECC, Ann Arbor, Michigan 48105, and the ^¶Department of Developmental Biology, Stanford University School of Medicine, Stanford California 94305

Abstract

In Caenorhabditis elegans,lin-2, lin-7, and lin-10genetically interact to control the trafficking of the Let-23 growth factor receptor to the basolateral surface of body epithelia. The human homologue of the lin-10 gene has recently been identified as a member of the X11 gene family. The X11 proteins contain one phosphotyrosine binding (PTB) and two PSD-95·Dlg·ZO-1 (PDZ) domains as well as an extended amino terminus. We have previously shown that the PTB domain of X11α (also known as Mint1) can bind to the amyloid precursor protein (APP) in a phosphotyrosine-independent fashion and can markedly inhibit the processing of APP to the amyloid β (Aβ) peptide. Here, we report that X11α directly binds to the mammalian homologue of Lin-2 (mLin-2), also known as CASK. This binding is mediated by direct interaction between the Calmodulin Kinase II (CKII)-like domain of mLin-2 and the amino terminus of X11α. Furthermore, we can detect direct interactions between mLin-2 and mammalian Lin-7 (mLin-7). In mouse brain, we have identified a heterotrimeric complex that contains mLin-2, mLin-7, and X11α and that is likely important for the localization of proteins in polarized cells. This complex may play an important role in the trafficking and processing of APP in neurons.

Footnotes

↵* The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank™/EMBL Data Bank with accession number(s) AF070975.
↵‡ Investigator of the Howard Hughes Medical Institute. To whom correspondence should be addressed: Howard Hughes Medical Institute, University of Michigan Medical Ctr., Rm. 4570, MSRB II, 1150 W. Medical Center Dr., Ann Arbor, MI 48109-0650; Tel.: 734-764-3567; Fax: 734-763-9323; E-mail: bmargoli{at}uv1.im.med.umich.edu.
↵2 C. V. Whitfield, C. Benard, T. Barnes, S. Hekimi, and S. K. Kim, manuscript submitted.
↵3 J.-P. B., M. D.-B., and B. M., unpublished observations.
↵4 S. Straight, J.-P. Borg, and B. Margolis, unpublished observations.
Abbreviations:

PTB

phosphotyrosine binding domain

PDZ

PSD-95·Dlg·ZO-1

APP

amyloid precursor protein

CKII

calmodulin-dependent kinase II

mLin-2

mammalian Lin-2

mLin-7

mammalian Lin-7

Aβ

amyloid beta

EST

expressed sequence tag

GST

glutathioneS-transferase

HA

hemagglutinin

HRP

horseradish peroxidase

PAGE

polyacrylamide gel electrophoresis

TBS

Tris-buffered saline

GK

guanylate kinase

EGF

epidermal growth factor.
- Received August 24, 1998.
- Revision received October 5, 1998.
The American Society for Biochemistry and Molecular Biology, Inc.