BLOC-1 function in cargo sorting towards lysosome-related organelles

Tuesday, October 25, 2011 — Poster Session II
Noon – 2:00 p.m.	Natcher Conference Center	NICHD	CELLBIO-20

* FARE Award Winner

Authors

• C Schindler
• D Nemecek
• A Steven
• J Bonifacino

Abstract

Biogenesis of lysosome-related organelle complexes (BLOC) are specifically involved in protein trafficking from endosomes to lysosome-related organelles (LROs), but not to conventional lysosomes. Mutations in these complexes, or in the endosomal cargo sorting complex Adaptor protein-3 (AP-3), cause Hermansky-Pudlak-Syndrome as consequence of defective LRO biogenesis. The octameric BLOC-1 complex is required to transport critical components of LROs, but its molecular function remains elusive. For this study, we expressed and purified octameric BLOC-1 from E. coli. We characterized the overall structure of purified BLOC-1 by negative staining EM and mapped individual subunits within the complex. Additional studies showed that recombinant BLOC-1 directly and specifically interacts with the core region of AP-3, which is involved in cargo recognition and with the cytosolic tails of the LRO-destined cargo proteins Trp1, Tyrosinase and Pmel17, but not with cargo for conventional lysosomes, indicating that BLOC-1 is a co-factor for AP-3-dependent sorting towards LROs. Moreover BLOC-1 specifically interacts with the endosomal SNARE proteins Syntaxin13 and SNAP-25, suggesting that BLOC-1 might regulate SNARE-dependent fusion processes. We plan to elucidate the molecular role of BLOC-1 by establishing a network of interactions and by functionally linking these to well-understood steps in cargo sorting and LRO biogenesis.

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