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Structural and biochemical properties show ARL3-GDP as a distinct GTP binding protein
R C Hillig1, M Hanzal-Bayer, M Linari
1Max-Planck-Institut für Molekulare Physiologie, Abteilung Strukturelle Biologie, Dortmund, Germany.
Structure (London, England : 1993)
|February 24, 2001
Summary
Arf-like protein 3 (ARL3) crystal structure reveals unique GDP binding independent of magnesium. This suggests ARL proteins may require specific effectors for activation, differing from Arf proteins.
Area of Science:
- Molecular Biology
- Structural Biology
- Biochemistry
Background:
- Arf-like (ARL) proteins are part of the Ras-related GTP binding protein superfamily.
- Their precise cellular functions remain largely unknown, though intracellular transport regulation is proposed.
- ARL proteins are found across diverse species in multiple isoforms.
Purpose of the Study:
- To elucidate the structural characteristics of the ARL3 subgroup of Ar proteins.
- To understand the mechanism of nucleotide binding and potential conformational changes in ARL3.
- To differentiate the activation mechanisms of ARL proteins from classical Arf proteins.
Main Methods:
- X-ray crystallography of murine ARL3-GDP at 1.7 Å resolution.
- Kinetic experiments using fluorescently labeled guanosine diphosphate (GDP).
Main Results:
- The crystal structure revealed an N-terminal extension of ARL3 anchored hydrophobically.
- ARL3-GDP binding is tight and independent of magnesium ions, attributed to a unique lysine residue.
- A beta sheet register shift is proposed to occur upon GTP binding, similar to Arf proteins.
Conclusions:
- ARL3 and ARL2 are distinct from Arf proteins due to their magnesium-independent GDP binding site.
- ARL protein activation may not require membrane association, unlike Arf proteins.
- ARL protein activation likely depends on effector proteins that stabilize GTP binding, rather than guanine nucleotide exchange factors (GEFs).