title: The adaptor function of TRAPPC2 in mammalian TRAPPs explains TRAPPC2-associated SEDT and TRAPPC9-associated congenital intellectual disability.
abstract: BACKGROUND
  The TRAPP (Transport protein particle) complex is a conserved protein complex functioning at various steps in vesicle transport. Although yeast has three functionally and structurally distinct forms, TRAPPI, II and III, emerging evidence suggests that mammalian TRAPP complex may be different. Mutations in the TRAPP complex subunit 2 (TRAPPC2) cause X-linked spondyloepiphyseal dysplasia tarda, while mutations in the TRAPP complex subunit 9 (TRAPPC9) cause postnatal mental retardation with microcephaly. The structural interplay between these subunits found in mammalian equivalent of TRAPPI and those specific to TRAPPII and TRAPPIII remains largely unknown and we undertook the present study to examine the interaction between these subunits. Here, we reveal that the mammalian equivalent of the TRAPPII complex is structurally distinct from the yeast counterpart thus leading to insight into mechanism of disease.
  
  
  RESULTS
  We analyzed how TRAPPII- or TRAPPIII- specific subunits interact with the six-subunit core complex of TRAPP by co-immunoprecipitation in mammalian cells. TRAPPC2 binds to TRAPPII-specific subunit TRAPPC9, which in turn binds to TRAPPC10. Unexpectedly, TRAPPC2 can also bind to the putative TRAPPIII-specific subunit, TRAPPC8. Endogenous TRAPPC9-positive TRAPPII complex does not contain TRAPPC8, suggesting that TRAPPC2 binds to either TRAPPC9 or TRAPPC8 during the formation of the mammalian equivalents of TRAPPII or TRAPPIII, respectively. Therefore, TRAPPC2 serves as an adaptor for the formation of these complexes. A disease-causing mutation of TRAPPC2, D47Y, failed to interact with either TRAPPC9 or TRAPPC8, suggesting that aspartate 47 in TRAPPC2 is at or near the site of interaction with TRAPPC9 or TRAPPC8, mediating the formation of TRAPPII and/or TRAPPIII. Furthermore, disease-causing deletional mutants of TRAPPC9 all failed to interact with TRAPPC2 and TRAPPC10.
  
  
  CONCLUSIONS
  TRAPPC2 serves as an adaptor for the formation of TRAPPII or TRAPPIII in mammalian cells. The mammalian equivalent of TRAPPII is likely different from the yeast TRAPPII structurally.
authors.affiliation: School of Biomedical Sciences, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong SAR, People's Republic of China.
authors.forename: Min
authors.initials: M
authors.lastname: Zong
authors.forename: Xing-gang
authors.initials: XG
authors.lastname: Wu
authors.forename: Cecilia W L
authors.initials: CW
authors.lastname: Chan
authors.forename: Mei Y
authors.initials: MY
authors.lastname: Choi
authors.forename: Hsiao Chang
authors.initials: HC
authors.lastname: Chan
authors.forename: Julian A
authors.initials: JA
authors.lastname: Tanner
authors.forename: Sidney
authors.initials: S
authors.lastname: Yu
mesh_terms: D000818:Animals; D016466:CHO Cells; D019556:COS Cells; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D006224:Cricetinae; D003412:Cricetulus; D040181:Genetic Diseases, X-Linked / Q000235:genetics / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D008607:Intellectual Disability / Q000235:genetics / Q000378:metabolism*; D036341:Intercellular Signaling Peptides and Proteins; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D009154:Mutation; D010009:Osteochondrodysplasias / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D036341:Intercellular Signaling Peptides and Proteins; D026901:Membrane Transport Proteins; C120759:TRAPPC2 protein, human; C569828:TRAPPC8 protein, human; C503887:TRAPPC9 protein, human; D014157:Transcription Factors; D033921:Vesicular Transport Proteins; C406327:transport protein particle, TRAPP; D049452:Green Fluorescent Proteins