Structural elements of ADP-ribosylation factor 1 required for functional interaction with cytohesin-1.
ADP-ribosylation factor 1 (ARF1) is a 20-kDa guanine nucleotide-binding protein involved in vesicular trafficking. Conversion of inactive ARF-GDP to active ARF-GTP is catalyzed by guanine nucleotide exchange proteins such as cytohesin-1. Cytohesin-1 and its Sec7 domain (C-1Sec7) exhibit guanine nucleotide exchange protein activity with ARF1 but not ARF-like protein 1 (ARL1), which is 57% identical in amino acid sequence. With chimeric proteins composed of ARF1 (F) and ARL1 (L) sequences we identified three structural elements responsible for this specificity. Cytohesin-1 increased [35S]guanosine 5'-(gamma-thio)triphosphate binding to L28/F (first 28 residues of L, remainder F) and to a much lesser extent F139/L, and mut13F139/L (F139/L with random sequence in the first 13 positions) but not Delta13ARF1 that lacks the first 13 amino acids; therefore, a nonspecific ARF N terminus was required for cytohesin-1 action. The N terminus was not, however, required for that of C-1Sec7. Both C-1Sec7 and cytohesin-1 effectively released guanosine 5'-(gamma-thio)triphosphate from ARF1, but only C-1Sec7 displaced the nonhydrolyzable GTP analog bound to mut13F139/L, again indicating that structure in addition to the Sec7 domain is involved in cytohesin-1 interaction. Some element(s) of the C-terminal region is also involved, because replacement of the last 42 amino acids with ARL sequence in F139L decreased markedly the interaction with cytohesin-1. Participation of both termini is consistent with the crystallographic structure of ARF in which the two terminal alpha-helices are in close proximity. ARF1 residues 28-50 are also important in the interaction with cytohesin-1; replacement of Lys-38 with Gln, the corresponding residue in ARL1, abolished the ability to serve as substrate for cytohesin-1 or C-1Sec7. These studies have defined multiple structural elements in ARF1, including switch 1 and the N and C termini, that participate in functional interactions with cytohesin-1 (or its catalytic domain C-1Sec7), which were not apparent from crystallographic analysis.
Pacheco-Rodriguez
G
G
Pulmonary-Critical Care Medicine Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892, USA. PachecoG@gwgate.nhlbi.nih.gov
Patton
W A
WA
Adamik
R
R
Yoo
H S
HS
Lee
F J
FJ
Zhang
G F
GF
Moss
J
J
Vaughan
M
M
D020823:ADP-Ribosylation Factor 1; D020727:ADP-Ribosylation Factors; D000595:Amino Acid Sequence; D000818:Animals; D002384:Catalysis; D002417:Cattle; D015815:Cell Adhesion Molecules / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors; D006150:Guanine Nucleotides / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid
D015815:Cell Adhesion Molecules; D020662:Guanine Nucleotide Exchange Factors; D006150:Guanine Nucleotides; C100723:cytohesin-1; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D019204:GTP-Binding Proteins; D020823:ADP-Ribosylation Factor 1; D020727:ADP-Ribosylation Factors