A subcomplex comprising TRAPPC11, TRAPPC12, TRAPPC13 and the fungal TRAPPC2L homolog, Tca17, directs TRAPPIII to autophagy.

Transport protein particle complexes (TRAPPs) are master regulators of membrane trafficking. TRAPPs are targeted to different locales by pathway-specific subunits decorating a core hetero-heptamer to build TRAPPII (Golgi exit) and TRAPPIII (autophagosomes and ER-Golgi trafficking). Metazoan and Arabidopsis TRAPPIII have three components, TRAPPC11, TRAPPC12 and TRAPPC13 (hereafter denoted TRAPPC11/12/13), that are absent from budding yeast. We studied TRAPPC11/12/13 in the related ascomycete Aspergillus nidulans, where TRAPPC11 and TRAPPC12 localize to pre-autophagosomes and their ablation impairs autophagy. We found that two stable subcomplexes containing Tca17, the homolog of metazoan TRAPPC2L, coexist - one includes the TRAPPII-specific subunits Trs120, Trs130 and Trs65 whereas the other contains the TRAPPIII-specific subunits TRAPPC11/12/13. Both are recruited to core TRAPP by Tca17, which therefore plays a crucial role by determining the physiological role of TRAPP. TRAPPIII also exists in two versions, TRAPPIIIa and TRAPPIIIb, both of which contain Trs85, the homolog of metazoan TRAPPC8, but with only TRAPPIIIb containing TRAPPC11/12/13, which target TRAPPIII to autophagy. This study might help characterize potentially pathogenic mutations affecting human TRAPPC11/12/13, facilitating assessment of their functional consequences in a genetically amenable ascomycete.