Crystal structure of [Leu1]zervamicin, a membrane ion-channel peptide: implications for gating mechanisms.

Abstract

Structures in four different crystal forms of [Leul'zervamicin (zervamicin Z-L, Ac-Leu-Ile-Gln-Iva-11e5-Thr-Aib-Leu-Aib-Hypl0-Gln-Aib-Hyp-Aib-Prol5-Phol, whereIva is isovaline, Aib is a-amino isobutyric acid, Hyp is 4-hydroxyproline, and Phol is phenylalaninol), a membrane channelforming polypeptide from Emericellopsis salmosynnemata, have been determined by x-ray diffraction. (Table 1). In each of the four different crystal forms, space groups P21 and P212121, the peptide molecules associate to form similar discontinuous water channels, which appear to give further insights into the nature of an ion channel, a possible gating mechanism, and the dynamics of a bent helix molecule. EXPERIMENTAL PROCEDURES [Leu']Zervamicin was isolated from a heterogeneous zervamicin mixture by HPLC on a reverse-phase C18 column, as described (10). Crystals were grown by slow evaporation of methanol/water solution or by vapor diffusion of water into ethylene glycol/ethanol solutions containing about 3 mg of peptide in 0.4 ml of solvent. X-ray diffraction data were measured with a four-circle automated diffractometer with CuK,,a radiation on crystals under the conditions listed in Table 1 for a best set of data. Lowering the temperature for some of the crystal forms resulted in shattering the crystal. Rapid scan speeds, 7-15°/min, were used in order to collect most ofthe data before significant deterioration ofthe crystal.The structures were solved by a vector-search procedure (11) contained in the SHELX84 package of programs (MicroVAX version of the SHELXTL system of programs; Siemens Instruments, Madison, WI). The search model was based on the backbone atoms ofthe known structure ofa 16-residue apolar analog of zervamicin (12) and was followed by a partialstructure procedure (13) by which the atoms in the side chains were located. The detailed structure only of crystal A will be reported here. Full-matrix anisotropic least-squares refineAbbreviations: Aib, a-aminoisobutyric acid (a-methylalanine); Hyp, 4-hydroxyproline; Iva, isovaline (a-ethylalanine); Phol, phenylalaninol. 5307The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Folding, aggregation and molecular recognition in peptides

“…Linear peptides form fl-sheets (Karle, Karle, Mastropaolo, Camerman & Camerman, 1983), 3,0-helices for short peptides (Toniolo et al, 1983), ahelices for longer peptides Fox & Richards, 1982), double helices (Benedetti, di Blasio, Pedone, Lorenzi, Tomasic & Gramlich, 1979;Langs, 1988) and mixed helices consisting of a 3,0/ahelix and a fl-ribbon twisted into a helix (Karle, Flippen-Anderson, Sukumar & Balaram, 1987;Karle, Flippen-Anderson, Agarwalla & Balaram, 1991). The latter has been established in Leu-zervamicin and a 16-residue apolar analog that contain in their sequences three Pro or Hyp (hydroxyproline) residues at positions 10, 13 and 15.…”

Stereochemical Control of Peptide Folding

“…6(b)), While the former provides an example of approximately four turns of a straight helix, 58 the latter adopts a curved or bent structure due to the presence of as many as three Pro/Hyp residues in the C-terminus segment. 59 There has been considerable discussion in the literature on the nature of the helical conformations adopted by Aib rich sequences. 51,53,60,61 Both 3 10 and a-helical conformations have been characterized depending upon peptide length, sequence and Aib content.…”

Crystal structure of the channel-forming polypeptide antiamoebin in a membrane-mimetic environment

“…Crystal structure determination of alamethicin (4) and Leu 1 -zervamicin (5)(6)(7)(8) have provided details of the stereochemistry of these transmembrane helices and their models of association, leading to suggestions for plausible mechanisms of voltage gating (3)(4)(5). Thus far, crystal structures for these membrane-active peptides have been obtained without any cocrystallized lipid component.…”