Spontaneous assembly of a self-complementary oligopeptide to form a stable macroscopic membrane.

Abstract

A 16-residue peptide [(Ala-Glu-Ala-Glu-AlaLys-Ala-Lys)2J has a characteristic 13-sheet circular dichroism spectrum in water. Upon the addition of salt, the peptide spontaneously assembles to form a macroscopic membrane. The membrane does not dissolve in heat or in acidic or alkaline solutions, nor does it dissolve upon addition of guanidine hydrochloride, SDS/urea, or a variety of proteolytic enzymes.Scanning EM reveals a network of interwoven framents ""10-20 nm in diameter. An important component of the stability is probably due to formation of complementary ionic bonds between glutamic and lysine side chains. This phenomenon may be a model for studying the insoluble peptides found in certain neurological disorders. It may also have implications for biomaterials and origin-of-life research.Peptides of alternating hydrophilic and hydrophobic amino acid residues have a tendency to adopt a (3-sheet structure. The complete sequence of (Ala-Glu-Ala-Glu-Ala-Lys-AlaLys)2 (EAK16) was originally found in a region of alternating hydrophobic and hydrophilic residues in zuotin, a yeast protein that was initially identified for its ability to bind preferentially to left-handed Z-DNA (1). Previous studies with alternating amphiphilic-peptide polymers-e.g., poly-(Val-Lys), poly(Glu-Ala), poly(Tyr-Glu), poly(Lys-Phe), poly(Lys-Leu)-and oligopeptides [(Val-Glu-Val-Orn)j_3]-Val (2-7) have shown that these polymers can adopt (3-sheet structures and can aggregate, depending upon pH, salt, and time. However, self-complementary EAK16 is distinctive in that it forms an insoluble macroscopic membrane. MATERIALS AND METHODSPeptides. The Glu-Ala-Lys peptides were synthesized by a peptide synthesizer (Applied Biosystems), purified by reverse-phase HPLC, and eluted by a linear gradient of 5-80% acetonitrile/0.1% trifluoacetic acid. The peptide stock solutions were dissolved in water (1-5 mg/ml) or in 23% acetonitrile (10 mg/ml). The concentrations of the peptides were determined by dissolving dried peptide in water (wt/vol) and centrifuging the solution. A portion of the solution was then analyzed by hydrolysis with internal controls. The sequence of the peptides was confirmed by microsequencing. The composition of the peptides was confwrmed by hydrolytic analysis. Ala-Glu-Ala-Lys-Ala-Glu-Ala-Glu-Ala-Lys-AlaLys (EAK12) and EAK16 are acetylated and aminated at the N-and C-terminal ends, respectively. Blocking of both N and C termini of EAK16 appears nonessential for membrane formation.CD Measurement. CD spectra were gathered on an Aviv model 6ODS spectropolarimeter with 6OHDS software for data processing. Because EAK16 contains both positively and negatively charged residues, the peptide itself can serve as a buffer. CD samples were prepared by diluting stock peptide solution (1-5 mg/ml) in water.Membrane Preparations. The membranes were prepared as follows: 5-10 ,4 of the stock solution of EAK16 peptide (1-5 mg/ml) was added to 0.5-1.0 ml of phosphate-buffered saline (150 mM NaCl/10 mM sodium phosphate, pH 7.4) with 0.00001% Con...

Biomimetic materials for tissue engineering

“…In water, they freely organize themselves into stable β-sheet structures. When exposed to monovalent alkaline cations or physiological conditions, the oligopeptides can assemble into hydrogels with interwoven nano-fibers with a diameter of 10-20 nm [74,75]. Self-assembly has also been shown by molecules other than peptides or PAs [76].…”

Redox modulated hydrogelation of a self-assembling short peptide amphiphile

“…Peptide self-assembly is driven by the orchestrated interaction of several intermolecular non-covalent forces including hydrogen bonding, π-π stacking, hydrophobic effect and electrostatic interactions. Environmental stimuli including pH [16][17][18][19], ionic strength and/or metal ions [18,[20][21][22], temperature [23], light [24] and enzyme-triggers [25], provide powerful approaches for modulating hydrogelation. Furthermore, introduction of microenvironment-sensitive amino acid residues into peptide sequences is also an important strategy for controlling peptide self-assembly and hydrogelation [9,[26][27][28].…”

Conformationally driven protease‐catalyzed splicing of peptide segments: V8 protease‐mediated synthesis of fragments derived from thermolysin and ribonuclease A

“…The reasons for this are not readily apparent. However, the formation of P-sheet structures are reported for peptides containing a combination of Ala, Glu, and Lys residues (Zhang et al, 1993), as are a-helical conformations for peptides of the same composition but with a different sequence (Marqusee & Baldwin, 1987). Recently, a 16-mer peptide containing 14 Ala residues flanked by lysine was shown to exhibit highly stable P-sheet conformation (Forood et al, 1995).…”