The penta-EF-hand protein ALG-2 interacts with a region containing PxY repeats in Alix/AIP1, which is required for the subcellular punctate distribution of the amino-terminal truncation form of Alix/AIP1.
ALG-2 is a Ca(2+)-binding protein that belongs to the penta-EF-hand protein family and associates with several proteins, including annexin VII, annexin XI, and Alix/AIP1, in a Ca(2+)-dependent manner. The yeast two-hybrid system and a biotin-tagged ALG-2 overlay assay were carried out to characterize the interaction between ALG-2 and Alix. The region corresponding to amino acid residues 794 to 827 in the carboxy-terminal proline-rich region of Alix was sufficient to confer the ability to interact directly with ALG-2. This region includes four-tandem PxY repeats. Alanine substitutions indicated that seven proline residues in this region, four in the PxY repeats, and four tyrosine residues in the PxY repeats are crucial for the binding affinity with ALG-2. Endogenous ALG-2 was co-immunoprecipitated in the presence of Ca(2+) with FLAG-tagged Alix or FLAG-tagged Alix Delta EBS, a deletion mutant lacking the endophilin binding consensus sequence, but not with FLAG-tagged Alix Delta ABS, another mutant lacking the region comprising amino acids 798-841, from the lysates of HEK293 cells transfected with each FLAG-tagged protein expression construct. FLAG-tagged ALG-2 overexpressed in HEK293 cells was also co-immunoprecipitated with Alix in a Ca(2+)-dependent fashion, whereas FLAG-tagged ALG-2(E47A/E114A), a Ca(2+)-binding deficient mutant of ALG-2, was not detected in the immunoprecipitates of Alix even in the presence of Ca(2+). Fluorescent microscopic analyses using the carboxy-terminal half of Alix fused with green fluorescent protein (GFP-AlixCT) revealed that endogenous ALG-2 in HeLa cells exhibits a dot-like pattern overlapping with exogenously expressed GFP-AlixCT, and the distribution of GFP-AlixCT Delta ABS is observed diffusely in the cytoplasm. These results indicate the requirement of ABS in Alix for the efficient accumulation of AlixCT and raise the possibility that ALG-2 participates in membrane trafficking through a Ca(2+)-dependent interaction with Alix.
Laboratory of Molecular and Cellular Regulation, Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601.
Hideki
H
Shibata
Keiko
K
Yamada
Takako
T
Mizuno
Chiharu
C
Yorikawa
Hiroshi
H
Takahashi
Hirokazu
H
Satoh
Yasuyuki
Y
Kitaura
Masatoshi
M
Maki
D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D051017:Apoptosis Regulatory Proteins; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins; D002460:Cell Line; D020832:EF Hand Motifs; D056827:Endosomal Sorting Complexes Required for Transport; D051528:Guanylate Kinases; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D017354:Point Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary / Q000235:genetics; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D020449:Repetitive Sequences, Amino Acid; D013347:Subcellular Fractions / Q000378:metabolism; D020798:Two-Hybrid System Techniques
D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D056827:Endosomal Sorting Complexes Required for Transport; C097753:PDCD6 protein, human; C117020:PDCD6IP protein, human; D011506:Proteins; D051528:Guanylate Kinases; C485777:MAGI2 protein, human