Mutational analysis of βCOP (Sec26p) identifies an appendage domain critical for function
1 Graduate Program in Comparative Biomedical Sciences, Cornell University, Ithaca NY 14853, USA
2 Graduate Program in Pharmacology, Cornell University, Ithaca, NY 14853, USA
3 Graduate Program in Biophysics, Cornell University, Ithaca, NY 14853, USA
4 Department of Molecular Medicine, Cornell University, Ithaca, NY 14853, USA
5 Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA
6 Department of Molecular Medicine, Cornell University, C4-109 Veterinary Medical Center, Ithaca, NY 14853, USA
BMC Cell Biology 2008, 9:3 doi:10.1186/1471-2121-9-3Published: 22 January 2008
The appendage domain of the γCOP subunit of the COPI vesicle coat bears a striking structural resemblance to adaptin-family appendages despite limited primary sequence homology. Both the γCOP appendage domain and an equivalent region on βCOP contain the FxxxW motif; the conservation of this motif suggested the existence of a functional appendage domain in βCOP.
Sequence comparisons in combination with structural prediction tools show that the fold of the COOH-terminus of Sec26p is strongly predicted to closely mimic that of adaptin-family appendages. Deletion of the appendage domain of Sec26p results in inviability in yeast, over-expression of the deletion construct is dominant negative and mutagenesis of this region identifies residues critical for function. The ArfGAP Glo3p was identified via suppression screening as a potential downstream modulator of Sec26p in a manner that is independent of the GAP activity of Glo3p but requires the presence of the COOH-terminal ISS motifs.
Together, these results indicate an essential function for the predicted βCOP appendage and suggest that both COPI appendages perform a biologically active regulatory role with a structure related to adaptin-family appendage domains.