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T Blundell

Publications and source records attributed to T Blundell.

At least 37 records · Page 2Linked to original sources
PubMed1987

The structure of a synthetic pepsin inhibitor complexed with endothiapepsin.

The conformation of a synthetic polypeptide inhibitor, bound to the active site of the fungal aspartic proteinase endothiapepsin (EC 3.4.23.6), has been determined by X-ray diffraction at 0.20-nm resolution and refined to an agreement factor of 0.20. The inhibitor: Pro Thr Glu Phe-R-Phe Arg Glu (R = -CH2NH-) is based on a chromogenic substrate of pepsin (EC 3.4.23.1). It has, in place of the scissile bond, a reduced peptide group which is resistant to hydrolysis and mimics the tetrahedral transition state. The inhibitor binds in an extended conformation with the reduced bond close to the essential aspartate side-chains of the enzyme. The hydrogen bonds and hydrophobic interactions between the enzyme and the inhibitor do not induce large conformational changes.

Aspartic Acid Endopeptidases↗
PubMed1987

Crystallographic studies of reduced bond inhibitors complexed with an aspartic proteinase.

To aid in the design of an effective inhibitor to human renin, it is essential to have a detailed knowledge of how this aspartic proteinase interacts with its substrate, angiotensinogen. Human renin shows a stringent specificity toward the Leu-Val bond in its natural substrate. The minimal length for an effective substrate has been characterised as an octapeptide sequence derived from the amino terminal portion of angiotensinogen (residues 6----13): His-Pro-Phe-His-Leu-Val-Ile-His (Leu-Val is the scissile bond). This suggests that renin has a fairly extensive active site cleft, as has been observed in homologous enzymes whose three-dimensional structures have been solved using x-ray diffraction methods. The homologous fungal aspartic proteinase, endothiapepsin, has been cocrystallised with human renin inhibitors of the type His-Pro-Phe-His-Leu-R-Val-Ile-His, where R indicates a reduced carbonyl analogue of the scissile peptide bond. The three-dimensional crystallographic structures of two complexes of endothiapepsin with an inhibitor have been solved. The details of inhibitor binding at the active site cleft of endothiapepsin are described. These data allow a rational approach to the design of novel renin inhibitors, through studies of these inhibitors in a three-dimensional model of human renin constructed in our laboratory.

Amino Acid Sequence↗
PubMed1985

The conformation of insulin-like growth factors: relationships with insulins.

The insulin-like growth factors and hystricomorph insulins have been modelled by interactive computer graphics on the assumption that their sequence homology to insulin implies that they will have a similar tertiary structure. These studies suggest that, although the insulin-related molecules can adopt the insulin fold, they are unlikely to form hexamers and if they form dimers they will be of reduced stability. The non-suppressibility of insulin-like growth factors by anti-insulin antibodies is explained in terms of differences of surface residues in the region A8-A10 and B1-B5. Receptor affinity of insulins and insulin-like growth factors for insulin receptors is explicable in terms of a receptor-binding site in the vicinity of B25 Phe on the insulin surface. An equivalent region around B25 Tyr of insulin-like growth factors may be responsible for their binding to type 1 receptors, although binding type 2 receptors must involve a different surface region not shared by insulin.

Amino Acid Sequence↗
PubMed1984

The active site of aspartic proteinases.

The active site of the aspartic proteinase, endothiapepsin, has been defined by X-ray analysis and restrained least-squares refinement at 2.1 A resolution with a crystallographic agreement value of 0.16. The environments of the two catalytically important aspartyl groups are remarkably similar and the contributions of the NH2- and COOH-terminal domains to the catalytic centre are related by a local 2-fold axis. The carboxylates of the aspartyls share a hydrogen bond and have equivalent contacts to a bound water molecule or hydroxonium ion lying on the local diad. The main chains around 32 and 215 are connected by a novel interaction involving diad-related threonines. It is suggested that the two pKa values of the active site aspartyls arise from a structure not unlike that in maleic acid with a hydrogen-bonded intermediate species and a dicarboxylate characterised by electrostatic repulsions between the two negatively charged groups.

Amino Acid Sequence↗
PubMed1984

Computer graphics modelling of human renin. Specificity, catalytic activity and intron-exon junctions.

A model has been constructed using computer graphics for human renin based on the sequence derived from that of the gene and the 3-dimensional structure defined at high resolution for other homologous aspartic proteinases. Human renin can adopt a 3-dimensional structure close to that of other aspartic proteinases, in which amino acids corresponding to intron-exon junctions in the gene are at surface regions in the 3-dimensional structure. As expected, the essential catalytic residues are retained and the nearby residue 304 is alanine as in the mouse sequence, supporting the idea that Asp 304 of other aspartic proteinases may contribute to the low pH of their optimal activity. There are interesting differences at subsite S3' which may contribute to the specificity of human renin. Certain residues at the surface of the enzyme adjacent to the active site cleft are unique to renins and may play a role in recognition and binding of angiotensinogen.

Amino Acid Sequence↗
PubMed1984

The molecular structures and interactions of bovine and human gamma-crystallins.

Knowledge of the three-dimensional structure of bovine gamma II-crystallin has provided the basis for building molecular models using computer graphics of two human gamma-crystallins, the sequences of which have recently been determined. The tertiary structures of these gamma-crystallins are predicted to be highly conserved. They have extensive networks of interacting charges on their surfaces, which may contribute to their thermodynamic stability and partially define the degree of water retention in the lens. The human crystallins appear to be more hydrophobic than the bovine molecule. All have arrangements of cysteine thiols which may be important as electron sinks and reserve redox potential in the normal lens but which may contribute to protein aggregation in cataract.

Amino Acid Sequence↗
PubMed1984

Evolution in the insulin family: molecular clocks that tell the wrong time.

The sequences, three-dimensional structures and biological activities of insulins and the related insulin-like growth factors demonstrate many changes that have occurred in evolution. In the hystricomorph rodent insulins this has led to insulins which differ not only from those of other mammals but also amongst themselves. They show no single characteristic substitution but generally exhibit reduced anabolic activity, increased growth promoting effects and inability to form oligomers. Their divergence is discussed in terms of orthologous evolution implying very variable rates of accepted mutations, and paralogous evolution for which a minimal hypothesis must be several silently evolving genes.

Amino Acid Sequence↗
PubMed1983

X-ray analysis of the eye lens protein gamma-II crystallin at 1.9 A resolution.

We report the X-ray structure analysis and refinement at 1.9 A resolution of calf gamma-II crystallin, a lens-specific protein. The sequence of Croft (1972) has been modified to give a polypeptide chain of 174 residues (cf. 165). The protein has a symmetrical, hierarchical structure of two globular domains each comprising two similar "Greek key" motifs, consecutive along the polypeptide chain, and related by a pseudo 2-fold axis. The two domains pack together with a single connection and are related by a further pseudo 2-fold axis which bisects the angle between the intra-domain dyads. Forty-two pairs of C alpha positions for the two most similar motifs have root-mean-square separation at best fit of 0.69 A. The N and C-terminal domains gave root-mean-square separation of 0.89 A for 82 pairs of C alpha atoms at best fit. In each domain the two Greek key motifs form a pair of four-stranded antiparallel beta-pleated sheets, each sheet composed of three stands from one motif and one from the other. The sheets pack together in a wedge shape, closed at the top by the loops connecting the third and fourth strands of each motif. The first two strands of each motif form an extended beta-hairpin which is folded on to the beta-sheet. The packing of each motif into the globular domains involves a staggered bilayer of side-chains between each pair of beta-sheets which does not preserve the pseudo 2-fold axes observed in the C alpha position topology. In the core of each domain there are interactions between polarizable aromatic groups and sulphur-containing residues which may contribute to stability and may also serve to protect aromatic side-chains from ultraviolet light damage in the lens. At the surface of the molecule over half the ionic side-chains are closely paired, which probably stabilizes the tertiary fold and may reduce the water bound. Crystal lattice interactions are described which may be similar to those occurring in vivo in the lens between crystallins. Seven cysteine residues have been identified in the structure and these may have a role in the thermodynamic stability of the molecule, its intermolecular interactions under the normal reducing conditions of the lens, and also in the aggregation and cross-linking which occur in some forms of cataract. Three of these residues, Cys18, Cys23 and Cys74, form a cluster in the N-terminal domain.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1981

The molecular structure and stability of the eye lens: x-ray analysis of gamma-crystallin II.

The three-dimensional structure of the eye lens protein, bovine gamma-crystallin II, has been determined at 2.6 A resolution. The protein has a tow domain beta-structure, folded into four remarkably similar 'Greed key' motifs, and shows the highest internal symmetry of any protein studied by X-ray analysis. Although the symmetrical structure seems very stable, the arrangement of the sulphydryl groups would allow intramolecular cross-linking leading to possible destabilization, and intermolecular cross-linking leading to aggregation, both of which may be important to cataract formation.

Amino Acid Sequence↗
PubMed1981

A monomeric insulin from the casiragua: molecular model building using computer graphics.

Interactive computer graphics have been used to construct a three-dimensional model of casiragua insulin assuming a tertiary structural homology with that of porcine insulin. The hydrophobic core of the molecule is conserved, but the hydrophobic surfaces involved in formation of dimers and hexamers in porcine insulin are more hydrophilic and contain charged residues. These observations are consistent with a close similarity of the far ultra violet circular dichroism of casiragua insulin and porcine insulin, and with the inability of casiragua insulin to self-associate. The low receptor-binding potency appears to result mainly from the substitution of B26-tyrosine by an arginine.

Animals↗
PubMed1977

X-ray analysis and circular dichroism of the acid protease from Endothia parasitica and chymosin.

The structure of an acid proteinase from Endothia parasitica has been solved by x-ray diffraction using multiple isomorphous replacement. A 3 A resolution map was interpreted in terms of a bilobal structure with a long 25 A cleft. The secondary structure is mostly distorted beta-sheet. The circular dichroism was measured and model curves for different secondary structures were fitted by least squares indicating a large component of beta-structure. The structure was seen to be homologous with that of the acid proteinase from R. Chinensis and hence with pepsin and chymosin. A rotation function against diffraction data from chymosin crystals confirm confirm this and suggested an approach to the solution of this structure.

Ascomycota↗