Expression of Concern: N-terminal palmitoylation within the appropriate amino acid environment conveys on NOS2 the ability to progress along the intracellular sorting pathways. J. Cell Sci. doi: 10.1242/jcs.02878

Following elucidation of the structures of the flavin components of succinate dehydrogenase (SD) as N (3) -histidyl-8α-FAD and of monoamine oxidase (MAO) as cysteinyl-8α-FAD and determination of the peptide sequences around the flavin sites of these enzymes, attention has been focused on the covalently bound FAD of Chromatium cytochrome c-552. As documented in preliminary communications, the FAD moiety of this enzyme is also substituted at the 8α-position, as judged from ESR hyderfine structure of the free radical cation and the characteristic hypsochromic shift of the second absorption band of the neutral flavoquinone in purified preparations of the flavin. Definite proof has come from the liberation of 8-carbxyriboflavin on performic acid treatment of the enzyme. In regard to ESR and optical spectra and the tendency of the purified flavin (liberated by proteolysis) to undergo autooxidation with a further hypsochromic shift of the second absorption band and increased fluorescence, the flavin resembles the MAO flavin. The fact that fluorescence is >90% quenched at all pH values even at the FMN level and doees not vary with pH between 3.2 and 8 also suggests a thioether linkage as in cysteinyl riboflavin. In many respects, however, the Chromatium flavin differs from cysteinyl riboflavin. Highly purified preparations from tryptic-chymotryptic digests give a positive chloroplatinic test. Electrophoresis clearly shows the presence of carboxyl and amino groups but the peptide gives no characteristic ninhydrin reaction and amino acid analysis of performic acid oxidized samples yields cysteic acid and threonine in amounts less than equimolar to the flavin. The amino acid environment around the flavin may account for these results although a linkage other than a thioether remains a possibility.

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Amino Acids Regulate Retrieval of the Yeast General Amino Acid Permease from the Vacuolar Targeting Pathway

Molecular Biology of the Cell ◽

10.1091/mbc.e05-07-0669 ◽

2006 ◽

Vol 17 (7) ◽

pp. 3031-3050 ◽

Cited By ~ 55

Author(s):

Marta Rubio-Texeira ◽

Chris A. Kaiser

Keyword(s):

Amino Acids ◽

Plasma Membrane ◽

Amino Acid ◽

Membrane Trafficking ◽

Amino Acid Permease ◽

A Genome ◽

High Amino Acid ◽

General Amino Acid Permease ◽

Intracellular Sorting ◽

Amino Acid Concentrations

Intracellular sorting of the general amino acid permease (Gap1p) in Saccharomyces cerevisiae depends on availability of amino acids such that at low amino acid concentrations Gap1p is sorted to the plasma membrane, whereas at high concentrations Gap1p is sorted to the vacuole. In a genome-wide screen for mutations that affect Gap1p sorting we identified deletions in a subset of components of the ESCRT (endosomal sorting complex required for transport) complex, which is required for formation of the multivesicular endosome (MVE). Gap1p-GFP is delivered to the vacuolar interior by the MVE pathway in wild-type cells, but when formation of the MVE is blocked by mutation, Gap1p-GFP efficiently cycles from this compartment to the plasma membrane, resulting in unusually high permease activity at the cell surface. Importantly, cycling of Gap1p-GFP to the plasma membrane is blocked by high amino acid concentrations, defining recycling from the endosome as a major step in Gap1p trafficking under physiological control. Mutations in LST4 and LST7 genes, previously identified for their role in Gap1p sorting, similarly block MVE to plasma membrane trafficking of Gap1p. However, mutations in other recycling complexes such as the retromer had no significant effect on the intracellular sorting of Gap1p, suggesting that Gap1p follows a genetically distinct pathway for recycling. We previously found that Gap1p sorting from the Golgi to the endosome requires ubiquitination of Gap1p by an Rsp5p ubiquitin ligase complex, but amino acid abundance does not appear to significantly alter the accumulation of polyubiquitinated Gap1p. Thus the role of ubiquitination appears to be a signal for delivery of Gap1p to the MVE, whereas amino acid abundance appears to control the cycling of Gap1p from the MVE to the plasma membrane.

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Amino acid environment determines expression of carbamoylphosphate synthetase and phosphoenolpyruvate carboxykinase in embryonic rat hepatocytes

In Vitro Cellular & Developmental Biology ◽

10.1007/bf02623291 ◽

1985 ◽

Vol 21 (11) ◽

pp. 606-611 ◽

Cited By ~ 5

Author(s):

Wouter H. Lamers ◽

Marian Roon ◽

Piet G. Mooren ◽

André Graaf ◽

Robert Charles

Keyword(s):

Amino Acid ◽

Phosphoenolpyruvate Carboxykinase ◽

Rat Hepatocytes ◽

Carbamoylphosphate Synthetase ◽

Acid Environment

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Intracellular sorting and targeting of melanosomal membrane proteins: identification of signals for sorting of the human brown locus protein, gp75.

The Journal of Cell Biology ◽

10.1083/jcb.130.4.807 ◽

1995 ◽

Vol 130 (4) ◽

pp. 807-820 ◽

Cited By ~ 111

Author(s):

S Vijayasaradhi ◽

Y Xu ◽

B Bouchard ◽

A N Houghton

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Membrane Proteins ◽

Surface Protein ◽

Melanin Pigment ◽

Pigment Synthesis ◽

Amino Terminal ◽

Cytoplasmic Organelles ◽

Intracellular Sorting ◽

Carboxy Terminal

The structural and functional integrity of cytoplasmic organelles is maintained by intracellular mechanisms that sort and target newly synthesized proteins to their appropriate cellular locations. In melanocytic cells, melanin pigment is synthesized in specialized organelles, melanosomes. A family of melanocyte-specific proteins, known as tyrosinase-related proteins that regulate melanin pigment synthesis, is localized to the melanosomal membrane. The human brown locus protein, tyrosinase-related protein-1 or gp75, is the most abundant glycoprotein in melanocytic cells, and is a prototype for melanosomal membrane proteins. To investigate the signals that allow intracellular retention and sorting of glycoprotein (gp)75, we constructed protein chimeras containing the amino-terminal extracellular domain of the T lymphocyte surface protein CD8, and transmembrane and cytoplasmic domains of gp75. In fibroblast transfectants, chimeric CD8 molecules containing the 36-amino acid cytoplasmic domain of gp75 were retained in cytoplasmic organelles. Signals in the gp75 cytoplasmic tail alone, were sufficient for intracellular retention and targeting of the chimeric proteins to the endosomal/lysosomal compartment. Analysis of subcellular localization of carboxy-terminal deletion mutants of gp75 and the CD8/gp75 chimeras showed that deletion of up amino acids from the gp75 carboxyl terminus did not affect intracellular retention and sorting, whereas both gp75 and CD8/gp75 mutants lacking the carboxyl-terminal 27 amino acids were transported to the cell surface. This region contains the amino acid sequence, asn-gln-pro-leu-leu-thr, and this hexapeptide is conserved among other melanosomal proteins. Further evidence showed that this hexapeptide sequence is necessary for intracellular sorting of gp75 in melanocytic cells, and suggested that a signal for sorting melanosomal proteins along the endosomal/lysosomal pathway lies within this sequence. These data provide evidence for common signals for intracellular sorting of melanosomal and lysosomal proteins, and support the notion that lysosomes and melanosomes share a common endosomal pathway of biogenesis.

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