title: XC1028 from Xanthomonas campestris adopts a PilZ domain-like structure without a c-di-GMP switch.
abstract: The crystal structure of XC1028 from Xanthomonas campestris has been determined to a resolution of 2.15 A using the multiple anomalous dispersion approach. It bears significant sequence identity and similarity values of 64.10% and 70.09%, respectively, with PA2960, a protein indispensable for type IV pilus-mediated twitching motility, after which the PilZ motif was first named. However, both XC1028 and PA2960 lack detectable c-di-GMP binding capability. Although XC1028 adopts a structure comprising a five-stranded beta-barrel core similar to other canonical PilZ domains with robust c-di-GMP binding ability, considerable differences are observed in the N-terminal motif; XC1028 assumes a compact five-stranded beta-barrel without an extra long N-terminal motif, whereas other canonical PilZ domains contain a long N-terminal sequence embedded with an essential "c-di-GMP switch" motif. In addition, a beta-strand (beta1) in the N-terminal motif, running in exactly opposite polarity to that of XC1028, is found inserted into the parallel beta3/beta1' strands, forming a completely antiparallel beta4 downward arrow beta3 upward arrow beta1 downward arrow beta1' upward arrow sheet in the canonical PilZ domains. Such dramatic structural differences at the N-terminus may account for the diminished c-di-GMP binding capability of XC1028, and suggest that interactions with additional proteins are necessary to bind c-di-GMP for type IV fimbriae assembly.
authors.affiliation: Institute of Biochemistry, National Chung-Hsing University, Taichung, 40227, Taiwan, Republic of China.
authors.forename: Tso-Ning
authors.initials: TN
authors.lastname: Li
authors.forename: Ko-Hsin
authors.initials: KH
authors.lastname: Chin
authors.forename: Jyung-Hurng
authors.initials: JH
authors.lastname: Liu
authors.forename: Andrew H-J
authors.initials: AH
authors.lastname: Wang
authors.forename: Shan-Ho
authors.initials: SH
authors.lastname: Chou
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D006152:Cyclic GMP / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D040681:Structural Homology, Protein; D016959:Xanthomonas campestris / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; C097615:PilZ protein, Pseudomonas aeruginosa; D006152:Cyclic GMP