Par-3 is a cell-polarity protein that regulates the formation of tight junctions (TJs) in epithelial cells, where claudin is a major cell-cell adhesion molecule (CAM). TJs are formed at the apical side of adherens junctions (AJs), where Ecadherin and nectin are major CAMs. We have revealed that nectin first forms cell-cell adhesions, and then recruits cadherin to nectin-based cell-cell adhesion sites to form AJs and subsequently recruits claudin to the apical side of AJs to form TJs. The cytoplasmic tail of nectin binds afadin and Par-3. Afadin regulates the formation of AJs and TJs cooperatively with nectin. Here, we studied the role of Par-3 in the formation of these junctions by using Par-3-knockdown MDCK cells. Par-3 was necessary for the formation of AJs and TJs but was not necessary for nectinbased cell-cell adhesion. Par-3 promoted the association of afadin with nectin, whereas afadin was not necessary for the association of Par-3 with nectin. However, the association of afadin with nectin alone was not sufficient for the formation of AJs or TJs, and Par-3 and afadin cooperatively regulated it. We describe here these novel roles of Par-3 in the formation of junctional complexes.

SYNOPSISAn apolar synthetic octapeptide, Boc-( Ala-Aib),-OMe, was crystallized in the triclinic space group P1 with cell dimensions a = 11.558 A, b = 11.643 A, c = 9.650 A, a = 120.220", 8 = 107.000", y = 90.430", V = 1055.889 A3, 2 = 1, CsrHsoOllNe.H20. The calculated crystal density was 1.217 g/cm3 and the absorption coefficient p was 6.1. All the intrahelical hydrogen bonds are of the 310 type, but the torsion angles, C # J and $, of Ala( 5) and Ala( 7) deviate from the standard values. The distortion of the 310-helix at the C-terminal half is due to accommodation of the bulky Boc group of an adjacent peptide in the packing. A water molecule is held between the N-terminal of one peptide and the C-terminal of the other. The oxygen atom of water forms hydrogen bonds with N( 1) -H and N( 2 ) -H, which are not involved in the intrahelical hydrogen bonds. The hydrogen atoms of water also formed hydrogen bonds with carbonyl oxygens of the adjacent peptide molecule. On the other hand, 'H-nmr analysis revealed that the octapeptide took an a-helical structure in a CD3CN solution. The longer peptides, Boc-( Ala-Aib)6-OMe and Boc-( Ala-Aib)8-OMe, were also shown to take an a-helical structure in a CD3CN solution. An a-helical conformation of the hexadecapeptide in the solid state was suggested by x-ray analysis of the crystalline structure. Thus, the critical length for transition from the 310-to a-helix of Boc-(Ala-Aib),-OMe is 8. 0 1993 John Wiley & Sons, Inc.

The three-dimensional structure of Cu,Zn-superoxide dismutase from spinach leaves has been determined by X-ray crystal structure analysis. The atomic coordinates were refined at 2.0 A resolution using the Hendrickson and Konnert program for stereochemically restrained refinement against structure factors, which allowed the use of non-crystallographic symmetry. The crystallographic residual error for the refined model was 24.9%, with a root mean square deviation of 0.03 A from the ideal bond length and an average atomic temperature factor of 9.6 A. A dimeric molecule of the enzyme is comprised of two identical subunits related by a non-crystallographic 2-fold axis. Each subunit of 154 amino acid residues is composed primarily of eight anti-parallel beta-strands that form a flattened cylinder, plus three external loops. The main-chain hydrogen bonds primarily link the beta-strands. The overall structure of this enzyme is quite similar to that of the bovine dismutase except for some parts. The single disulfide bridge (Cys57-Cys146) and the salt bridge (Arg79-Asp101) may stabilize the loop regions of the structure. The Cu2+ and Zn2+ ions in the active site lie 6.1 A apart at the bottom of the long channel. The Cu2+ ligands (ND1 of His-46, and NE2 of His-48, -63, and -120) show an uneven tetrahedral distortion from a square plane. The Zn2+ ligands (ND1 of His-63, -71, and -80 and OD1 of Asp-83) show an almost tetrahedral geometry. The imidazole ring of His-63 forms a bridge between the Cu2+ and Zn2+ ions.(ABSTRACT TRUNCATED AT 250 WORDS)

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We have determined the crystal structures of two types of human basic fibroblast growth factor, the serine analogue and the wild-type, at 1.6 and 2.5 A resolution, respectively. Two good heavy atom derivatives were found and used for multiple isomorphous replacement phasing. The atomic coordinates were refined using the Hendrickson & Konnert program for stereochemically restrained refinement against structure factors. The crystallographic R factors were reduced to 15.3% for the serine analogue structure and 16.0% for the wild-type structure. The serine analogue and wild-type structures have been found to be almost identical, the root-mean-square deviation between the corresponding C alpha atoms being 0.11 A. Their structures are composed of twelve beta-strands forming a barrel and three loops. Their molecules have an approximate threefold internal symmetry and are similar in architecture to that of interleukin-1 beta. A possible heparin-binding site, which comprises five basic residues, Lys119, Arg120, Lys125, Lys129, and Lys135, has been revealed by calculating the electrostatic potential energy.