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Updated: May 30, 2026

In vivo and in vitro Studies of Adaptor-clathrin Interaction
Published on: January 26, 2011
Structure and function of ALG-2, a penta-EF-hand calcium-dependent adaptor protein
Masatoshi Maki1, Hironori Suzuki, Hideki Shibata
1Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan. mmaki@agr.nagoya-u.ac.jp
Apoptosis-linked gene 2 (ALG-2) is a calcium-dependent adaptor protein that binds to specific proline-rich motifs. Its structure and binding properties are crucial for protein complex stabilization in cellular transport systems.
Area of Science:
- Molecular Biology
- Structural Biology
- Cell Biology
Background:
- Apoptosis-linked gene 2 (ALG-2) is a highly conserved penta-EF-hand (PEF) protein found across eukaryotes.
- ALG-2 shares structural similarities with calpain subunits and forms homo- and heterodimers with peflin.
- Unlike calmodulin, ALG-2 binds proteins via distinct proline-rich motifs in a calcium-dependent manner.
Purpose of the Study:
- To elucidate the structural basis of ALG-2's protein interactions.
- To characterize the calcium-dependent binding mechanisms of ALG-2 and its isoforms.
- To understand ALG-2's role as an adaptor protein in cellular transport.
Main Methods:
- X-ray crystallography was used to determine the structures of ALG-2 and its complexes.
- Analysis of protein-protein interactions with various proline-rich motifs, including PPYP(X)nYP and PXPGF.
- Comparison of the binding capabilities of ALG-2 and its alternatively spliced isoform, ALG-2(ΔGF122).
Main Results:
- ALG-2 forms dimers with a common eight α-helix structure and anti-parallel EF5 pairing.
- Calcium binding to ALG-2 induces conformational changes, opening a pocket for PPYP motif binding.
- The ALG-2(ΔGF122) isoform loses ALIX binding but retains Sec31A binding, indicating motif specificity.
- ALG-2 dimers possess two binding sites, functioning as calcium-dependent adaptors in ESCRT and ER-to-Golgi transport.
Conclusions:
- ALG-2 acts as a versatile calcium-dependent adaptor protein, bridging protein complexes.
- Its distinct proline-binding motifs and calcium sensitivity enable specific interactions.
- ALG-2 plays a significant role in intracellular trafficking pathways, including ESCRT and ER-to-Golgi transport.
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