The Medium Subunits of Adaptor Complexes Recognize Distinct but Overlapping Sets of Tyrosine-based Sorting Signals

doi:10.1074/jbc.273.40.25915

The Medium Subunits of Adaptor Complexes Recognize Distinct but Overlapping Sets of Tyrosine-based Sorting Signals*

From The ^‡Division of Molecular Genetics, Chiba University Graduate School of Medicine, 1-8-1 Inohana, Chuo-ku, Chiba 260-8670, Japan and the ^§Cell Biology and Metabolism Branch, NICHD, National Institutes of Health, Bethesda, Maryland 20892

Abstract

Tyrosine-based sorting signals conforming to the motif YXXØ (Y is tyrosine, X is any amino acid, and Ø is an amino acid with a bulky hydrophobic side chain (leucine, isoleucine, phenylalanine, methionine, valine)) interact with the medium (μ) subunits of clathrin adaptor (AP) complexes. We have analyzed the selectivity of interaction between YXXØ signals and the μ1, μ2, and μ3 (A or B) subunits of the AP-1, AP-2, and AP-3 complexes, respectively, by screening a combinatorial XXXYXXØ library using the yeast two-hybrid system. All the medium subunits were found to prefer proline at position Y+2, suggesting that YXXØ signals are stabilized by a bend in the polypeptide backbone. Other than for this common preference, each medium subunit favored specific sets of residues at the X and Ø positions; these preferences were consistent with the proposed roles of the different adaptor complexes in rapid endocytosis and lysosomal targeting. A considerable specificity overlap was also revealed by these analyses, suggesting that additional factors, such as the context of the signals, must be important determinants of recognition.

Footnotes

↵* This work was supported in part by grants-in-aids for scientific research from the Ministry of Education, Science, and Culture of Japan (to H. O. and T. S.), the Naito Foundation (to H. O.), and the Uehara Memorial Foundation (to H. O.).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.
↵¶ To whom correspondence should be addressed: NICHD, National Institutes of Health, Bldg. 18T Rm. 101, 18 Library Dr., MSC 5430, Bethesda, MD 20892-5430. Tel.: 301-496-6368; Fax: 301-402-0078; E-mail:juan{at}helix.nih.gov.
Abbreviations:

TGN

trans-Golgi network

3AT

3-amino-1,2,4-triazole

SED

standard error of the difference.
- Received May 27, 1998.
The American Society for Biochemistry and Molecular Biology, Inc.