title: Solution structure of ApaG from Xanthomonas axonopodis pv. citri reveals a fibronectin-3 fold.
abstract: ApaG proteins are found in a wide variety of bacterial genomes but their function is as yet unknown. Some eukaryotic proteins involved in protein-protein interactions, such as the human polymerase delta-interacting protein (PDIP38) and the F Box A (FBA) proteins, contain ApaG homology domains. We have used NMR to determine the solution structure of ApaG protein from the plant pathogen Xanthomonas axonopodis pv. citri (ApaG(Xac)) with the aim to shed some light on its molecular function. ApaG(Xac) is characterized by seven antiparallel beta strands forming two beta sheets, one containing three strands (ABE) and the other four strands (GFCC'). Relaxation measurements indicate that the protein has a quite rigid structure. In spite of the presence of a putative GXGXXG pyrophosphate binding motif ApaG(Xac) does not bind ATP or GTP, in vitro. On the other hand, ApaG(Xac) adopts a fibronectin type III (Fn3) fold, which is consistent with the hypothesis that it is involved in mediating protein-protein interactions. The fact that the proteins of ApaG family do not display significant sequence similarity with the Fn3 domains found in other eukaryotic or bacterial proteins suggests that Fn3 domain may have arisen earlier in evolution than previously estimated.
authors.affiliation: Department of Chemical Science and Technology, University of Rome, Tor Vergata, Italy.
authors.forename: Daniel O
authors.initials: DO
authors.lastname: Cicero
authors.forename: Gian M
authors.initials: GM
authors.lastname: Contessa
authors.forename: Thelma A
authors.initials: TA
authors.lastname: Pertinhez
authors.forename: Mariana
authors.initials: M
authors.lastname: Gallo
authors.forename: Angela M
authors.initials: AM
authors.lastname: Katsuyama
authors.forename: Maurizio
authors.initials: M
authors.lastname: Paci
authors.forename: Chuck S
authors.initials: CS
authors.lastname: Farah
authors.forename: Alberto
authors.initials: A
authors.lastname: Spisni
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D029681:Arabidopsis Proteins / Q000737:chemistry; D001426:Bacterial Proteins / Q000737:chemistry*; D019143:Evolution, Molecular; D005353:Fibronectins / Q000737:chemistry*; D018583:Pliability; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012996:Solutions; D053532:Xanthomonas axonopodis / Q000737:chemistry*
chemical_list: D029681:Arabidopsis Proteins; D001426:Bacterial Proteins; D005353:Fibronectins; D012996:Solutions