Translation rate of human tyrosinase determines its N-linked glycosylation level

Tyrosinase is a type I membrane glycoprotein essential for melanin synthesis. Mutations in tyrosinase lead to albinism due, at least in part, to aberrant retention of the protein in the endoplasmic reticulum and subsequent degradation by the cytosolic ubiquitin-proteasomal pathway. A similar prematu...

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Bibliographic Details
Published in:The Journal of biological chemistry 2001-02, Vol.276 (8), p.5924
Main Authors: Ujvari, A, Aron, R, Eisenhaure, T, Cheng, E, Parag, H A, Smicun, Y, Halaban, R, Hebert, D N
Format: Article
Language:English
Subjects:
Amino Acid Sequence
Animals
Cell-Free System
Cells, Cultured
Consensus Sequence
Endoplasmic Reticulum - metabolism
Glycosylation
Humans
Melanocytes - metabolism
Melanoma, Experimental - metabolism
Membrane Glycoproteins - biosynthesis
Mice
Monophenol Monooxygenase - biosynthesis
Protein Biosynthesis
Protein Processing, Post-Translational
Protein Transport
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Summary:Tyrosinase is a type I membrane glycoprotein essential for melanin synthesis. Mutations in tyrosinase lead to albinism due, at least in part, to aberrant retention of the protein in the endoplasmic reticulum and subsequent degradation by the cytosolic ubiquitin-proteasomal pathway. A similar premature degradative fate for wild type tyrosinase also occurs in amelanotic melanoma cells. To understand critical cotranslational events, the glycosylation and rate of translation of tyrosinase was studied in normal melanocytes, melanoma cells, an in vitro cell-free system, and semi-permeabilized cells. Site-directed mutagenesis revealed that all seven N-linked consensus sites are utilized in human tyrosinase. However, glycosylation at Asn-290 (Asn-Gly-Thr-Pro) was suppressed, particularly when translation proceeded rapidly, producing a protein doublet with six or seven N-linked core glycans. The inefficient glycosylation of Asn-290, due to the presence of a proximal Pro, was enhanced in melanoma cells possessing 2-3-fold faster (7.7-10.0 amino acids/s) protein translation rates compared with normal melanocytes (3.5 amino acids/s). Slowing the translation rate with the protein synthesis inhibitor cycloheximide increased the glycosylation efficiency in live cells and in the cell-free system. Therefore, the rate of protein translation can regulate the level of tyrosinase N-linked glycosylation, as well as other potential cotranslational maturation events.
ISSN:0021-9258
DOI:10.1074/jbc.M009203200