Publikationsdatum:
2015-03-23
Beschreibung:
The oligomeric complex transport protein particle I (TRAPPI) mediates nucleotide exchange on the RAB GTPase RAB1/Ypt1. TRAPPII is composed of TRAPPI plus three additional subunits, Trs120, Trs130, and Trs65. Unclear is whether TRAPPII mediates nucleotide exchange on RAB1/Ypt1, RAB11/Ypt31, or both. In Aspergillus nidulans, RabORAB1 resides in the Golgi, RabERAB11 localizes to exocytic post-Golgi carriers undergoing transport to the apex, and hypA encodes Trs120. RabERAB11, but not RabORAB1, immunoprecipitates contain Trs120/Trs130/Trs65, demonstrating specific association of TRAPPII with RabERAB11 in vivo. hypA1ts rapidly shifts RabERAB11, but not RabORAB1, to the cytosol, consistent with HypATrs120 being specifically required for RabERAB11 activation. Missense mutations rescuing hypA1ts at 42 °C mapped to rabE, affecting seven residues. Substitutions in six, of which four resulted in 7- to 36-fold accelerated GDP release, rescued lethality associated to TRAPPII deficiency, whereas equivalent substitutions in RabORAB1 did not, establishing that the essential role of TRAPPII is facilitating RabERAB11 nucleotide exchange. In vitro, TRAPPII purified with HypATrs120-S-tag accelerates nucleotide exchange on RabERAB11 and, paradoxically, to a lesser yet substantial extent, on RabORAB1. Evidence obtained by exploiting hypA1-mediated destabilization of HypATrs120/HypCTrs130/Trs65 assembly onto the TRAPPI core indicates that these subunits sculpt a second RAB binding site on TRAPP apparently independent from that for RabORAB1, which would explain TRAPPII in vitro activity on two RABs. Using A. nidulans in vivo microscopy, we show that HypATrs120 colocalizes with RabERAB11, arriving at late Golgi cisternae as they dissipate into exocytic carriers. Thus, TRAPPII marks, and possibly determines, the Golgi–to–post-Golgi transition.
Print ISSN:
0027-8424
Digitale ISSN:
1091-6490
Thema:
Biologie
,
Medizin
,
Allgemeine Naturwissenschaft
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