beta-structures of alternating polypeptides and their possible role in chemical evolution

Area of Science:

• Biochemistry
• Polymer Science
• Structural Biology

Background:

• The formation of water-soluble beta-structures in copolypeptides with alternating hydrophilic and hydrophobic residues is a known phenomenon.
• Previous studies demonstrated this for poly(Val-Lys).

Purpose of the Study:

• To generalize the formation of water-soluble beta-structures to other alternating copolypeptides.
• To investigate the effects of enantiomer substitution and disrupted alternation on beta-structure formation.
• To examine the binding properties of the resulting beta-surfaces.

Main Methods:

• Synthesis of optically pure alternating copolypeptides: poly(Lys-Leu-Lys-Leu) and poly(Leu-Glu-Leu-Glu).
• Introduction of enantiomeric L-lysyl residues and disruption of alternation with glycyl or L-prolyl residues.
• Use of strong interaction ions (perchlorate) and lengthening of alternating sequences in semi-random copolymers.
• Analysis of beta-structure formation and characterization using Circular Dichroism (CD) spectroscopy.

Main Results:

• Alternating copolypeptides poly(Lys-Leu-Lys-Leu) and poly(Leu-Glu-Leu-Glu) form water-soluble beta-structures.
• Enantiomer substitution (approx. 10% L-lysyl) did not prevent beta-transition but altered beta-structures.
• Disrupted alternation (poly(Gly-Lys-Leu-Lys-Leu), poly(Pro-Lys-Leu-Lys-Leu)) significantly reduced beta-structure formation.
• Soluble beta-structures were obtained using perchlorate ions or longer alternating sequences in semi-random copolymers, showing distinct CD spectra.

Conclusions:

• The tendency of alternating copolypeptides to form water-soluble beta-structures is a generalizable property.
• Structural modifications impact beta-structure formation and characteristics.
• Conditions involving strong ionic interactions or extended sequences can promote soluble beta-structure formation, with potential applications in studying surface binding properties.