title: Ca2+-loaded spherulin 3a from Physarum polycephalum adopts the prototype gamma-crystallin fold in aqueous solution.
abstract: Spherulin 3a is the most abundantly expressed cytosolic protein in spherulating plasmodia of the slime mold Physarum polycephalum. High yields of unlabeled, uniformly 15N and uniformly 13C/15N-labeled recombinant spherulin 3a from Escherichia coli could be produced by a simple protocol described here. The three-dimensional solution structure of Ca2+-loaded spherulin 3a was determined by homo- and heteronuclear NMR spectroscopy. The structure of monomeric spherulin 3a consists of two pleated beta-sheets plus a short alpha-helix arranged into the gamma-crystallin fold. The beta-sheets comprise two intertwined Greek-key motifs. An additional N-terminal beta-strand is unique to spherulin 3a. Complexation of calcium ions greatly enhances overall conformational stability of the protein. The average atomic root-mean-square deviations (r.m.s.d.) for heavy atoms in beta-strands were 0.34(+/-0.16) A for the backbone atoms and 0.73(+/-0.40) A for all atoms. The corresponding r.m.s.d. values for heavy atoms in the whole protein were 0.62(+/-0.42) A for the backbone atoms and 0.99(+/-0.65) A for all atoms. We show the structural relationship between spherulin 3a, a myxomycete dormancy protein, and crystallins from the vertebrate eye lens. Since spherulin 3a has a structure corresponding to one domain of bovine gammaB(II)-crystallin, it represents a hypothetical ancestral gamma-crystallin precursor structure.
authors.affiliation: Max-Planck-Institut für Biochemie, Martinsried, D-82152, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Rosinke
authors.forename: C
authors.initials: C
authors.lastname: Renner
authors.forename: E M
authors.initials: EM
authors.lastname: Mayr
authors.forename: R
authors.initials: R
authors.lastname: Jaenicke
authors.forename: T A
authors.initials: TA
authors.lastname: Holak
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium; D003046:Coccidioidin / Q000648:ultrastructure*; D003459:Crystallins / Q000737:chemistry*; D005656:Fungal Proteins / Q000737:chemistry / Q000648:ultrastructure*; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D016839:Physarum polycephalum / Q000737:chemistry*; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D015800:Protozoan Proteins; D011994:Recombinant Proteins
chemical_list: D003459:Crystallins; D005656:Fungal Proteins; D015800:Protozoan Proteins; D011994:Recombinant Proteins; C009303:spherulin; C108191:spherulin 3a protein, Physarum polycephalum; D003046:Coccidioidin; D002118:Calcium