SynopsisThe 36-amino acid avian pancreatic polypeptide has been studied by x-ray analysis a t 0.98-A resolution and refined using a restrained least-squares technique to an agreement factor of 15.6%. The polypeptide, which has a compact globular structure with a hydrophobic core, comprises a polyproline-like helix (residues 2-8) and an a-helix (residues 14-32). The molecule forms symmetrical dimers linked through zinc atoms in the crystal lattice. The high-resolution analysis defines sequence-dependent distortions in the a-helical parameters due to hydrogen bonding of water molecules and side chains. The thermal parameters indicate an increased flexibility of the main chain at the turn between the helices and in the C-terminal residues. For the first time, six-parameter anisotropic thermal ellipsoids have been refined for each atom; these define the directions of the molecular motions in the polypeptide, indicating concerted vibrations. The physiological roles of conformation, flexibility, and dynamics of this polypeptide hormone are discussed.

(Rcceiwd bcbrtiat-! 27. 19x4) ~ L J B 83 0215 Pancreatic polypeptide has been extracted and sequenced from a wide range of species. The 36-residue polypeptides have some hormonal characteristics, and show a high degree of sequence homology. Two recently isolated polypeptides, from porcine gut and brain, also show a high degree of sequence homology with the pancreatic polypeptides. It was proposed that these polypeptides were members of a related family.The X-ray determined structure of one member of the family, turkey pancreatic polypeptide, is known to high resolution, but there is no structural information for the others. Studies designed to give an insight into the tertiary structure of these related molecules have been carried out, including model building using interactive computer graphics, circular dichroic spectroscopy and secondary structure prediction using a variety of algorithms.The results indicate that a compact globular conformation, similar to that observed in turkey pancreatic polypeptide may be adopted by all molecules and that this may be more highly conserved than the individual amino acid sequences.Since the first identification of pancreatic polypeptide (PP) in the chicken pancreas [l], homologous peptides have been isolated from the alligator (Kimmel, unpublished results), the turkey [2], goose (Shen et al., unpublished results), ox, pig, sheep, dog and human [3]. These 36-residue polypeptides share a feature common to many gastroenteric hormones, a blocked. amidated carboxy terminus. Tatemoto and Mutt [4] used this feature to isolate possible hormonal peptides in tissue extracts and isolated, amongst others, two peptides, PYY from pig intestine [5] and NPY from pig brain tissue [6]. They showed that these polypeptides have considerable homology with the pancreatic polypeptides and proposed that PP, NPY and PYY form a newly recognised hormone family (see Table 1).The structure of one member of this family, turkey pancreatic polypeptide, has been determined by X-ray crystallography [2, 7, 81 and the analysis recently extended to very high resolution, d,,, = 98pm [9-111. The turkey PP protomer comprises of two segments of secondary structure: a polyproline type-I1 helix (residues 1-8) and an a-helix (residues 14-32). These helices, joined by a type-I1 fl-turn, interact via hydrophobic contacts to produce a compact and stable tertiary fold. The C-terminal region, residues 33 -36, extend away from the body of the molecule and display some flexibility in the crystal lattice. Further hydrophobic interactions are achieved by the formation of dimers in which a cage of aromatic residues, related by the crystallographic diad axis, is formed. In the crystal the dimers form extended oligomeric arrays via the coordination of a zinc ion. The zinc coordination involves His-34 Nt: of one, Asp-23 of another and the glycine nitrogen and carbonyl oxygen of a third dimer. The penta-,4hhrericr/ions. PP, pancreatic polypeptide; NPY, pig neuropolypcptide; PYY, pig intestinal polypeptide. coordinated site is c...

Abstract7B-crystallin is a structural protein of the eye lens with a role in the maintenance of an even distribution of protein and water over distances around the wavelength of light, preserving lens transparency. The structure of the 174-residue bovine protein has already been determined at room temperature to 1.47 A resolution. By flash freezing the protein crystals, data have now been collected to a nominal resolution limit of 1.2 A as radiation damage was essentially eliminated. The protein-water model has been refined against this data using the program RESTRAIN converging to an R factor of 18.5% with all data. Atomic positions are clearly indicated in the electron-density maps. Discrete bimodal disorder has been visualized for a few side chains. Out of a total of 498 water molecules present in the crystal asymmetric unit, 394 have been modelled and refined at unit occupancy. The solvent structure is extremely well ordered with an average B value of 23.4 A 2. Partially occupied sites have been identified where disorder in the protein induces concomitant disorder in the local solvent structure. The solvent structure covers 97% of the solvent-exposed surface of the protein in the crystal. 126 water molecules are distributed in second and higher hydration shells. There are networks of hydrogen-bonded solvent extending up to 64 molecules in a network, comprising trimers and tetramers as well as five-and six-membered water-ring structures. The hydration of the protein surface is dominated by arginine and aspartate side chains. Extensive cages of highly ordered solvent molecules are also observed around exposed non-polar groups.

The measurement of the longitudinal speed of sound in crystals of ribonuclease-A and in human haemoglobin using laser-generated ultrasound is reported. Average values of 1784 (72) m s -1 and 1828 m s -I were obtained. As a control the speed of sound transmitted through a compacted disc of lysozyme powder was measured as 2004 (23)

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The sequences of urokinase (UK) and tissue‐type plasminogen activator (TPA) were aligned with those of chymotrypsin, trypsin, and elastase according to their ‘structurally conserved regions’. In spite of its trypsin‐like specificity UK was model‐built on the basis of the chymotrypsin structure because of a corresponding disulfide pattern. The extra disulfide bond falls to cysteines 50 and 111d. Insertions can easily be accommodated at the surface. As they occur similarly in both, UK and TPA, a role in plasminogen recognition may be possible. Of the functional positions known to be involved in substrate or inhibitor binding, Asp 97, Lys 143 and Arg 217 (Leu in TPA) may contribute to plasminogen activating specificity. PTI binding may in part be impaired by structural differences at the edge of the binding pocket.

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