期刊
EMBO JOURNAL
卷 19, 期 2, 页码 187-198出版社
WILEY-BLACKWELL
DOI: 10.1093/emboj/19.2.187
关键词
endocytosis; internalization signal; protein targeting; receptor downregulation; ubiquitin
资金
- NIDDK NIH HHS [R01 DK053257, DK53257] Funding Source: Medline
- NIGMS NIH HHS [T32GM08061, T32 GM008061] Funding Source: Medline
Ubiquitin modification of signal transducing receptors at the plasma membrane is necessary for rapid receptor internalization and downregulation, We have investigated whether ubiquitylation alters a receptor cytoplasmic tail to reveal a previously masked internalization signal, or whether ubiquitin itself carries an internalization signal. Using an alpha-factor receptor-ubiquitin chimeric protein, we demonstrate that monoubiquitin can mediate internalization of an activated receptor that lacks all cytoplasmic tail sequences. Furthermore, fusion of ubiquitin in-frame to the stable plasma membrane protein Pma1p stimulates endocytosis of this protein. Ubiquitin does not carry a functional tyrosine- or di-leucine-based internalization signal. Instead, the three-dimensional structure of the folded ubiquitin polypeptide carries an internalization signal that consists of two surface patches surrounding the critical residues Phe4 and Ile44. We conclude that ubiquitin functions as a novel regulated internalization signal that can be appended to a plasma membrane protein to trigger downregulation.
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