High impact information on ARFIP1

• Here we show that Arfaptin binds specifically to GTP-bound Arf1 and Arf6, but binds to Rac.GTP and Rac.GDP with similar affinities [1].
• We show that this survival effect involves the ADP-ribosylation factor-interacting protein arfaptin 2, the levels of which are increased in HD patients [2].
• Arfaptin 1, a approximately 39-kDa protein based on the deduced amino acid sequence, had been initially identified in a yeast two-hybrid screen using dominant active ARF3 (Q71L) as bait with an HL-60 cDNA library [3].
• Arfaptin 2, found in the same two-hybrid screen as arfaptin 1, is 60% identical in amino acid sequence and may or may not have an analogous function [3].
• It was suggested that arfaptin 1 may be involved in Golgi functions, since the FLAG-tagged protein was associated with Golgi membranes when expressed in COS-7 cells and could be bound to Golgi in vitro in an ADP-ribosylation factor (ARF)- and GTPgammaS-dependent, brefeldin A-inhibited fashion [3].

Biological context of ARFIP1

• Employing yeast two-hybrid screening of an HL60 cDNA library using a constitutively active mutant of ARF3 (ARF3.Q71L), as a probe, we have identified a cDNA encoding a novel protein with a calculated molecular mass of 38.6 kDa, which we have named arfaptin 1 [4].
• Utilizing several deletion mutants of arfaptin 1 it is shown that the association of arfaptin 1 with myrARF3 is mediated via two binding sites on arfaptin 1 [5].

Anatomical context of ARFIP1

• When expressed in COS cells, arfaptin 1 was localized to the Golgi complex [4].
• Arfaptin 1 in cytosol was recruited to Golgi membranes by ARF in a guanosine 5'-O-(3-thiotriphosphate)-dependent and brefeldin A-sensitive manner [4].

Associations of ARFIP1 with chemical compounds

• Arfaptin effects on guanine nucleotide binding by ARFs were minimal whether or not a purified ARF guanine nucleotide-exchange protein was present [3].

Other interactions of ARFIP1

• Arfaptin 1 inhibited activation of both enzymes in a concentration-dependent manner and was without effect in the absence of ARF [3].
• However, a second group reported that POR1, a truncated form of arfaptin, bound to GTP-Rac1 [6].
• Here it is shown that the dimeric helical domain of Arfaptin superimposes with a monomeric helical domain from the Dbl homology domain of Tiam, a guanine nucleotide exchange factor (GEF) for Rac, in their respective complexes with Rac [7].
• PICK1 is a 416 amino acid protein that contains a PDZ domain, a coiled-coil motif/arfaptin homology domain and an acidic c-terminal [8].
• This view has been challenged by recent structural and biochemical studies of the Arfaptin/Por protein, which interacts equally well with the GDP- and GTP-bound forms of the G protein Rac [7].

References