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| Presenter: |
| Vankatesha Basrur |
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| Institute: |
Lab or Branch |
| NCI |
Laboratory of Cell Biology |
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| Title: |
| Proteomic analysis of early melanosomes |
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| Authors: |
| V. Basrur, F. Yang, T. Kushimoto, Y. Higashimoto,
K. Yasumoto, J. Valencia, J. Muller, W.D. Vieira, H. Watabe
H, J. Shabanowitz, V.J. Hearing, D.F. Hunt, E. Appella. |
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| Abstract: |
| Melanin, a heterogeneous biopolymer produced
by melanocytes and by retinal pigment epithelial cells,
is synthesized and deposited in specialized membrane-bound
organelles known as melanosomes. Based on their morphology
and degree of melanization, melanosomes have been classified
into four developmental stages (stage I-IV). The biogenesis
of melanosomes is still a hotly debated area of pigment
cell research. Observations that many human diseases affect
pigmentation and lysosomal function suggest that both
types of organelles are closely related. Study of pigmentation
disorders through genetic and biochemical approaches has
thus far identified only 6 proteins as melanosome specific
proteins. Most of the biochemical characterization has
been carried out on the fully mature stage III and IV
melanosomes. However, study of early stage melanosomes,
which might shed light on their biogenesis, is limited
because of the difficulty in obtaining them in sufficiently
pure form for analysis. In this study, we used free flow
electrophoresis to enrich early melanosomes (stage I and
II) followed by mass spectrometry to comprehensively identify
the melanosome proteome. Using this approach, all 6 of
the known melanosome-specific proteins have been identified,
as have 56 proteins that are shared with other organelles
and 6 that are novel. The localization of the 6 novel
proteins in melanosomes has been confirmed using Western
blotting and confocal immunohistochemistry. These results
indicate that melanosomes represent modified lysosomes
with several ER components and only contain a limited
number of specific proteins that provide the melanosome
with its unique architecture and function. |
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