PubMed Health⌕ Search

Biomedical subjects

M Perutz

Publications and source records attributed to M Perutz.

11 recordsLinked to original sources
PubMed1995

Incorporation of glutamine repeats makes protein oligomerize: implications for neurodegenerative diseases.

Many transcription factors and some other proteins contain glutamine repeats; their abnormal expansion has been linked to several dominantly inherited neuro-degenerative diseases. Having found that poly(L-glutamine) alone forms beta-strands held together by hydrogen bonds between their amide groups, we surmised that glutamine repeats may form polar zippers, an unusual motif for protein-protein interactions. To test this hypothesis, we have engineered a Gly-Gln10-Gly peptide into the inhibitory loop of truncated chymotrypsin inhibitor 2 (CI2), a small protein from barley seeds, by both insertion and replacement. Gel filtration resolved both mutant inhibitors into at least three fractions, which analytical ultracentrifugation identified as monomers, dimers, and trimers of the recombinant protein; the truncated wild-type CI2 formed only monomers. CD difference spectra of the dimers and trimers versus wild type indicated that their glutamine repeats formed beta-pleated sheets, while those of the monomers versus wild type were more suggestive of type I beta-turns. The CD spectra of all three fractions remained unchanged even after incubation at 70 degrees C; neither the dimers nor the trimers dissociated at this temperature. We argue that the stability of all three fractions is due to the multiplicity of hydrogen bonds between extended strands of glutamine repeats in the oligomers or within a beta-hairpin formed by the single glutamine repeat of each monomer. Pathological effects may arise when expanded glutamine repeats cause proteins to acquire excessively high affinities for each other or for other proteins with glutamine repeats.

Amino Acid Sequence↗
PubMed1994

Polar zippers: their role in human disease.

Ascaris hemoglobin consists of 8 subunits, each of which contains a C-terminal peptide with the sequence Glu-Glu-Lys-His repeated 4 times. When plotted on a beta-strand, this sequence leads to alternate lysines and glutamates on one side of the strand, and alternate glutamates and histidines on the other side, suggestive of a polar zipper that links the subunits together. A computer search of the protein database showed that the same or similar sequences also occur in other proteins. Some contain long repeats of Asp-Arg or Glu-Arg, among them the small nuclear ribonucleo-U1 70K protein, which is an autoantigen in systemic lupus erythematosis. These repeats appear to constitute the dominant epitopes in the autoimmune reaction. Single chains with Asp-Arg repeats may form alpha-helices in which alternate positively charged ridges and negatively charged grooves compensate each other. Several separate chains with Asp-Arg repeats could compensate each other's charges optimally by zipping together to beta-sheets. Several homeodomains of Drosophila, as well as the human transcription factor SP1, contain repeats of glutamines. Molecular modeling, circular dichroism, and electron and X-ray diffraction studies of a synthetic poly(L-glutamine) showed that it forms beta-sheets held together by hydrogen bonds between the main-chain and side-chain amides. Published data suggest that the function of these glutamine repeats consists of joining essential transcription factors bound to distant segments of DNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1992

Polar zipper sequence in the high-affinity hemoglobin of Ascaris suum: amino acid sequence and structural interpretation.

The extracellular hemoglobin of Ascaris has an extremely high oxygen affinity (P50 = 0.004 mmHg). It consists of eight identical subunits of molecular weight 40,600. Their sequence, determined by protein chemistry, shows two tandemly linked globin-like sequences and an 18-residue C-terminal extension. Two N-linked glycosylation sites contain equal ratios of mannose/glucosamine/fucose of 3:2:1. Electron micrographs suggest that the eight subunits form a polyhedron of point symmetry D4, or 42. The C-terminal extension contains a repeat of the sequence Glu-Glu-His-Lys, which would form a pattern of alternate glutamate and histidine side chains on one side and of glutamate and lysine side chains on the other side of a beta strand. We propose that this represents a polar zipper sequence and that the C-terminal extensions are joined in an eight-stranded beta barrel at the center of the molecule, with histidine and glutamate side chains inside and lysine and glutamate side chains outside the barrel compensating each other's charges. The amino acid sequence of Ascaris hemoglobin fails to explain its high oxygen affinity.

Amino Acid Sequence↗
PubMed1991

Involvement of the distal histidine in the low affinity exhibited by Hb Chico (Lys beta 66----Thr) and its isolated beta chains.

Hemoglobin (Hb) Chico (Lys beta 66----Thr at E10) has a diminished oxygen affinity (Shih, D. T.-b., Jones, R. T., Shih, M. F.-C., Jones, M. B., Koler, R. D., and Howard, J. (1987) Hemoglobin 11, 453-464). Our studies show that its P50 is about twice that of Hb A and that its cooperativity, anion, and Bohr effects between pH 7 and 8 are normal. The Bohr effect above pH 8 is somewhat reduced, indicating a small but previously undocumented involvement of the ionic bond formed by Lys beta 66 in the alkaline Bohr effect. Since the oxygen affinity of the alpha-hemes is likely to be normal, that of the beta-hemes in the tetramer is likely to be reduced by the equivalent of 1.2 kcal/mol beta-heme in binding energy. Remarkably, both initial and final stages of oxygen binding to Hb Chico are of lowered affinity relative to Hb A under all conditions examined. The isolated beta chains also show diminished oxygen affinity. In T-state Hb A, Lys(E10 beta) forms a salt bridge with one of the heme propionates, but comparison with other hemoglobin variants shows that rupture of this bridge cannot be the cause of the low oxygen affinity. X-ray analysis of the deoxy structure has now shown that Thr beta 66 either donates a hydrogen bond to or accepts one from His beta 63 via a bridging water molecule. This introduces additional steric hindrance to ligand binding to the T-state that results in slower rates of ligand binding. We measured the O2/CO partition coefficient and the kinetics of oxygen dissociation and carbon monoxide binding and found that lowered O2 and CO affinity is also exhibited by the R-state tetramers and the isolated beta chains of Hb Chico.

Carbon Monoxide↗
PubMed1990

Stereochemistry of carbon monoxide binding to normal human adult and Cowtown haemoglobins.

The structures of carbonmonoxyhaemoglobins A and Cowtown (His146 beta----Leu) have been refined at 2.2 A (1 A = 0.1 nm) and 2.3 A resolution, respectively. The least squares fit to the Fe-C-O line makes an angle to the haem normal of about 6 degrees. The Fe-C-O group is bent from linearity by about 7 degrees. The porphyrins in the CO liganded haemoglobins are ruffled. This deformation of the haem and the distortion of the Fe-C-O group may explain the low CO affinity of haemoglobin. The electron density for the C-terminal residues is low but sufficient to distinguish the histidyl and leucyl residues clearly. The similarity between these two structures, apart from 146 beta, means that the reduced alkaline Bohr effect is due solely to the replacement of histidine by a leucine.

Carbon Monoxide↗