Parallel packing of &#945;-helices in crystals of the zervamicin IIA analog Boc-Trp-Ile-Ala-Aib-Ile-Val-Aib-Leu-Aib-Pro-OMe.2H<SUB>2</SUB>0

An apolar synthetic analog of the first 10 residues at the NH2-terminal end of zervamicin HA crystallizes in the triclinic space group P1 with cell dimensions a = 10.206 &#177; 0.002 A, b = 12.244 &#177; 0.002 A, c = 15.049 &#177; 0.002 A, &#945; = 93.94 &#177; 0.01&#176;, &#946; = 95.10 &#177; 0.01&#176;, &#947; = 104.56 &#177; 0.01&#176;, Z = 1, C60H97N1103.2H2O. Despite the relatively few a-aminoisobutyric acid residues, the peptide maintains a helical form. The first intrahelical hydrogen bond is of the 310 type between N(3) and 0(0), followed by five &#945;-helix-type hydrogen bonds. Solution 1H NMR studies in chloroform also favor a helical conformation, with seven solvent-shielded NH groups. Continuous columns are formed by head-to-tail hydrogen bonds between the helical molecules along the helix axis. The absence of polar side chains precludes any lateral hydrogen bonds. Since the peptide crystallizes with one molecule in a trilinic space group, aggregation of the helical columns must necessarily be parallel rather than antiparallel. The packdng of the columns is rather inefficient, as indicated by very few good van der Waals' contacts and the occurrence of voids between the molecules

Conformation of a 16-residue zervamicin IIA analog peptide containing three different structural features: 3<SUB>10</SUB>-helix, &#945;-helix, and &#946;-bend ribbon

Boc-Trp-Ile-Ala-Aib-Ile-Val-Aib-Leu-Aib- Pro-Ala-Aib-Pro-Aib-Pro-Phe-OMe (where Boc is t-butoxycarbonyl and Aib is a-aminoisobutyric acid), a synthetic apolar analog of the membrane-active fungal peptide antibiotic zervamycin IIA, crystallizes in space group P1 with Z = 1 and cell parameters a = 9.086 &#177; 0.002 A:, b = 10.410 &#177; 0.002 A, c = 28.188 &#177; 0.004 A, &#945; = 86.13 &#177; 0.01&#176;, &#946; = 87.90 &#177; 0.01&#176;, and &#947; = 89.27 &#177; 0.01&#176;; overall agreement factor R = 7.3% for 7180 data (Fo &gt; 3&#963;) and 0.91-A resolution. The peptide backbone makes a continuous spiral that begins as a 310-helix at the N-terminus, changes to an &#945;-helix for two turns, and ends in a spiral of three &#946;-bends in a ribbon. Each of the &#946;-bends contains a proline residue at one of the corners. The torsion angles &#966;i range from -51&#176; to -91&#176; (average value -64&#176;), and the torsion angles &#968;i range from -1&#176; to -46&#176; (average value -31&#176;). There are 10 intramolecular NH-..OC hydrogen bonds in the helix and two direct head-to-tail hydrogen bonds between successive molecules. Two H20 and two CH3OH solvent molecules fill additional space with appropriate hydrogen bonding in the head-to-tail region, and two additional H20 molecules form hydrogen bonds with carbonyl oxygens near the curve in the helix at Pro-10. Since there is only one peptide molecule per cell in space group P1, the molecules repeat only by translation, and consequently the helices pack parallel to each other

Parallel packing of \alpha-helices in crystals of the zervamicin IIA analog Boc-Trp-Ile-Ala-Aib-Ile-Val-Aib-Leu-Aib-Pro-OMe 2H2O{2H}_2O

An apolar synthetic analog of the first 10 residues at the ${NH}_2$-terminal end of zervamicin IIA crystallizes in the triclinic space group P1 with cell dimensions a = 10.206 \pm 0.002 A, b = 12.244 \pm 0.002 A, c = 15.049 \pm 0.002 A, \alpha = 93.94 \pm 0.010, \beta = 95.10 \pm 0.010, \gamma = 104.56 \pm 0.01 deg, Z = 1, $C_{60}H_{97}N_{11}O_{13}.{2H}_2O$. Despite the relatively few \alpha-aminoisobutyric acid residues, the peptide maintains a helical form. The first intrahelical hydrogen bond is of the $3_{10}$ type between N(3) and O(0), followed by five \alpha-helix-type hydrogen bonds. Solution 1H NMR studies in chloroform also favor a helical conformation, with seven solvent-shielded NH groups. Continuous columns are formed by head-to-tail hydrogen bonds between the helical molecules along the helix axis. The absence of polar side chains precludes any lateral hydrogen bonds. Since the peptide crystallizes with one molecule in a trilinic space group, aggregation of the helical columns must necessarily be parallel rather than antiparallel. The packing of the columns is rather inefficient, as indicated by very few good van der Waals' contacts and the occurrence of voids between the molecules

Conformation of a 16-residue zervamicin IIA analog peptide containing three different structural features: 3103_{10}-helix, \alpha-helix, and \beta-bend ribbon

Boc-Trp-Ile-Ala-Aib-Ile-Val-Aib-Leu-Aib-Pro-Ala-Aib-Pro-Aib-Pro-Phe-OMe (where Boc is t-butoxycarbonyl and Aib is \alpha-aminoisobutyric acid), a synthetic apolar analog of the membrane-active fungal peptide antibiotic zervamycin IIA, crystallizes in space group P1 with Z = 1 and cell parameters a = 9.086 \pm 0.002 A, b = 10.410 \pm 0.002 A, c = 28.188 \pm 0.004 A, \alpha = 86.13 \pm 0.01 deg, \beta = 87.90 \pm 0.01 deg, and \gamma = 89.27 \pm 0.01 deg; overall agreement factor R = 7.3% for 7180 data ($F_o$ > 3\sigma) and 0.91-A resolution. The peptide backbone makes a continuous spiral that begins as a $3_{10}$-helix at the N-terminus, changes to an \alpha-helix for two turns, and ends in a spiral of three beta-bends in a ribbon. Each of the \beta-bends contains a proline residue at one of the corners. The torsion angles ${\phi}_i$ range from -51 deg to -91 deg (average value -64 deg), and the torsion angles ${\psi}_i$ range from -1 deg to -46 deg (average value -31 deg). There are 10 intramolecular NH...OC hydrogen bonds in the helix and two direct head-to-tail hydrogen bonds between successive molecules. Two $H_2O$ and two ${CH}_3OH$ solvent molecules fill additional space with appropriate hydrogen bonding in the head-to-tail region, and two additional $H_2O$ molecules form hydrogen bonds with carbonyl oxygens near the curve in the helix at Pro-10. Since there is only one peptide molecule per cell in space group P1, the molecules repeat only by translation, and consequently the helices pack parallel to each other

Crystallographic characterization of the conformation of the 1-aminocyclohexane-1-carboxylic acid residue in simple derivatives and peptides

The crystal structures of 1-aminocyclohexane-1-carboxylic acid (H-Acc6-OH) and six derivatives (including dipeptides) have been determined. The derivatives are Boc-Acc6-OH, Boc-(Acc6)2-OH, Boc-L-Met-Acc6-OMe, ClCH2CO-Acc6-OH, p-BrC6H4CO-Acc6-OH oxazolone, and the symmetrical anhydride from Z-Acc6-OH, [(Z-Acc6)2O]. The cyclohexane rings in all the structures adopt an almost perfect chair conformation. The amino group occupies the axial position in six structures; the free amino acid is the only example where the carbonyl group occupies an axial position. The values determined for the torsion angles about the N-C&#945; (&#934;) and C&#945;-CO (&#968;) bonds correspond to folded, potentially helical conformations for the Acc6 residue

Differences in hydration and association of helical Boc-Val-Ala-Leu-Aib-Val-Ala-Leu-(Val-Ala-Leu-Aib)2-OMe. xH2O in two crystalline polymorphs

The 15-residue apolar peptide, Boc-Val-Ala-Leu-Aib-Val-Ala-Leu-(Val-Ala-Leu-Aib)h2a-sO Mebeen crystallized from 2-propanol-water (form I). The crystal parameters for I are as follows:C74H133N15018*2H20s,p ace group P21, a = 9.185 (6) A, b = 47.410 (3) A, c = 10.325 (9) A, @ = 91.47(2)O, 2 = 2, R = 6.3% for 4532 reflections observed >3aQ, resolution 0.94 A. The structure isalmost completely a-helical with eleven 5-1 hydrogen bonds and one 441 hydrogen bond nearthe N-terminus. The structure has been compared with a polymorph (form 11) obtained frommethanol-water (Karle, I. L.; Flippen-Anderson, J. L.; Uma, K.; Sukumar, M.; Balaram, P., J. An.Chem. SOC19. 90,112,9350-9356). The two forms differ in the extent of hydration; form I contains two water molecules in the head-to-tail region of helical columns, while form I1 is more extensively solvated, with the equivalent of 7.5 water molecules. The three-dimensional packing of helices is completely parallel in I and antiparallel in 11

Crystallographic characterization of the conformation of the 1-aminocyclohexane-1-carboxylic acid residue in simple derivatives and peptides

The crystal structures of 1-aminocyclohexane-1-carboxylic acid (H-Acc6-OH) and six derivatives (including dipeptides) have been determined. The derivatives are Boc-Acc6-OH, Boc-(Acc6)2-OH, Boc-L-Met-Acc6-OMe, ClCH2CO-Acc6-OH, p-BrC6H4CO-Acc6-OH oxazolone, and the symmetrical anhydride from Z-Acc6-OH, [(Z-Acc6)2O]. The cyclohexane rings in all the structures adopt an almost perfect chair conformation. The amino group occupies the axial position in six structures; the free amino acid is the only example where the carbonyl group occupies an axial position. The values determined for the torsion angles about the N–Cα(φ) and Cα–CO (ψ) bonds correspond to folded, potentially helical conformations for the Acc6 residue