title: Structure and dynamics of the homodimeric dynein light chain km23.
abstract: km23 (96 residues, 11 kDa) is the mammalian ortholog of Drosophila roadblock, the founding member of LC7/robl/km23 class of dynein light chains. km23 has been shown to be serine-phosphorylated following TGFbeta receptor activation and to bind the dynein intermediate chain in response to such phosphorylation. Here, we report the three-dimensional solution structure of km23, which is shown to be that of a homodimer, similar to that observed for the heterodimeric complex formed between p14 and MP1, two distantly related members of the MglB/robl superfamily, but distinct from the LC8 and Tctex-1 classes of dynein light chains, which also adopt homodimeric structures. The conserved surface residues of km23, including three serine residues, are located predominantly on a single face of the molecule. Adjacent to this face is a large cleft formed by the incomplete overlap of loops from opposite monomers. As shown by NMR relaxation data collected at two fields, several cleft residues are flexible on the ns-ps and ms-mus timescales. Based on these observations, we propose that the patch of conserved residues on the central face of the molecule corresponds to the site at which km23 binds the dynein intermediate chain and that the flexible cleft formed between the overlap of loops from the two monomers corresponds to the site at which km23 binds other partners, such as the TGFbeta type II receptor or Smad2.
authors.affiliation: Department of Biochemistry, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA.
authors.forename: Udayar
authors.initials: U
authors.lastname: Ilangovan
authors.forename: Wei
authors.initials: W
authors.lastname: Ding
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhong
authors.forename: Christina L
authors.initials: CL
authors.lastname: Wilson
authors.forename: Jay C
authors.initials: JC
authors.lastname: Groppe
authors.forename: James T
authors.initials: JT
authors.lastname: Trbovich
authors.forename: Jorge
authors.initials: J
authors.lastname: Zúñiga
authors.forename: Borries
authors.initials: B
authors.lastname: Demeler
authors.forename: Qian
authors.initials: Q
authors.lastname: Tang
authors.forename: Guofeng
authors.initials: G
authors.lastname: Gao
authors.forename: Kathleen M
authors.initials: KM
authors.lastname: Mulder
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Hinck
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins / Q000235:genetics; D018360:Crystallography, X-Ray; D056445:Cytoplasmic Dyneins; D019281:Dimerization; D004330:Drosophila; D029721:Drosophila Proteins / Q000235:genetics; D004398:Dyneins / Q000737:chemistry* / Q000235:genetics; D006801:Humans; D007527:Isoenzymes / Q000737:chemistry / Q000235:genetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D011487:Protein Conformation; D012694:Serine / Q000737:chemistry
chemical_list: D002352:Carrier Proteins; C504797:DYNLRB1 protein, human; D029721:Drosophila Proteins; D007527:Isoenzymes; C120447:robl protein, Drosophila; D012694:Serine; D056445:Cytoplasmic Dyneins; D004398:Dyneins