Properties of the Interaction of Arf-like Protein 2 with PDEδ

Arf-like proteins (Arl) share certain characteristic features with the Arf subfamily of Ras superfamily proteins, but their function is unknown. Here, we show by a variety of spectroscopic techniques that Arl2, unlike most other Ras-related proteins, has micromolar rather than picomolar affinity for nucleotides. As a consequence of low affinity, nucleotide dissociation rates are rather fast, arguing that it is not regulated by guanine nucleotide exchange factors. Arl2 is isolated as prey in a yeast double hybrid screen using phosphodiesterase 6δ (PDEδ) as bait. This interaction is dependent on GTP, and the binding of PDEδ substantially stabilizes GTP binding, increasing affinity and decreasing dissociation rates by a similar factor. Among all Arl proteins tested, PDEδ only interacted with the closely related proteins Arl2 and Arl3, strongly suggesting that Arl2/3 are specific regulators of PDEδ.