title: Giardia gene predicts a 183 kDa nucleotide-binding head-stalk protein.
abstract: Previously described extended proteins from the cytoskeleton of Giardia lamblia (beta-giardin, median body protein) have been found to be segmented coiled coils with regular structural repeat patterns in their amino acid sequences. Screening a lambda ZAPII library derived from Giardia genomic DNA with an antibody directed against a 34 x 10(3) M(r) giardin isoform selected a gene encoding a much larger polypeptide chain (HPSR2), the sequence of which was determined by chromosome walking the open reading frame. The complete gene has been cloned and expressed as a recombinant protein of 183 x 10(3) M(r). The predicted amino acid sequence of the protein has identifiable features suggesting that it might be a motor protein with an amino-terminal hydrolytic domain attached to a long coiled coil stalk. The presumed head domain is 211 residues and contains a P-loop sequence conserved in purine nucleotide-binding proteins. The remaining 1409 amino acids mainly make up a region of heptad repeats such as in myosin or the kinesin stalk, ending in a small (67 amino acids) carboxy-terminal domain. Fourier analysis of the predicted stalk shows the presence of a strong physical repeat created by regular heptad phase changes dividing the coil into segments of 25 residues. This structure most closely resembles the smaller microtubule-associated median body protein which has segments of 24 residues.
authors.affiliation: Department of Life Science, Nottingham University, U.K..
authors.forename: J
authors.initials: J
authors.lastname: Marshall
authors.forename: D V
authors.initials: DV
authors.lastname: Holberton
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016386:Chromosome Walking; D003001:Cloning, Molecular; D017124:Conserved Sequence; D003598:Cytoskeletal Proteins / Q000096:biosynthesis / Q000235:genetics; D016054:DNA, Protozoan / Q000302:isolation & purification; D015870:Gene Expression; D015723:Gene Library; D017125:Genes, Protozoan; D016829:Giardia lamblia / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D016133:Polymerase Chain Reaction; D017433:Protein Structure, Secondary; D015800:Protozoan Proteins / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics*; D011817:Rabbits; D011994:Recombinant Proteins / Q000096:biosynthesis; D015183:Restriction Mapping; D017386:Sequence Homology, Amino Acid
chemical_list: D003598:Cytoskeletal Proteins; D016054:DNA, Protozoan; C096301:HPSR2 protein, Giardia intestinalis; D015800:Protozoan Proteins; D011994:Recombinant Proteins; C038207:giardin protein, Giardia lamblia