7.4 Reactive Chemical Systems: Effects of Nanoscale Chemical Heterogeneity on Hydrophobic Interactions and Molecular Assembly at Surfaces
Abstract
The objective of this effort is to understand higher order protein structure and elucidate new principles that govern protein assembly at surfaces. The proposal is divided into 3 key areas: 1) understanding the effects of chemical heterogeneity on hydrophobic interactions at surfaces; 2) understanding the modulation of hydrophobicity by proximal ionic groups of folded polypeptide-surface interactions: and 3) understanding the modulation of hydrophobicity of proximal ionic groups of folded poly-alpha-peptides in bulk aqueous solution. Focal Area I -This work will build upon the PJ s recent discovery that ions immobilized adjacent to non-polar domains can dramatically affect the strength of hydrophobic interactions and is ion type dependent. To understand the impact of geometrical variations in hdyrophobic-cationic nanopatterning, distinct and complementary systems will be investigated: i) alkanethiol self-assembled monolayer surfaces presenting both non-polar and polar terminated groups; and ii) helical oligomers of beta-peptides as a platform to generate chemical nanopattems that position charged and polar chemical functional groups adjacent to precisely defined non-polar domains. Hydrophobic and non-hydrophobic interactions will be quantified by comparing adhesive forces measured between the hydrophobic AFM tip and mixed SAM surfaces immersed in either aqueous solution or aqueous methanol mixture at different pHs and ionic strengths. Adhesion forces will also be measured with mixed SAM surfaces that present chemical patterns comprising an alkyl-terminated thiol and thiols terminated by a polar but uncharged group. Force measurements, as a function of methanol, pH, and ionic strength variations will be performed between the chemically functionalized AFM tip and single beta-peptide molecules presented from surfaces. Focal Area 2 - Peptide CC-Di derivatives will be designed to determine whether replacement of Lys resides with Arg residues at flanking positions will affect the hydrophobic driving force for coiled-coil dimerization. Variable temperature circular dichroism measurernents will be determined and T(m) values will be compared between the base peptide and peptide derivatives. Analytical ultracentrifugation studies will be carried out to verify dimer formation. Additional studies with CC-Di derivatives that do not contain acidic residues at g positions. and alpha-helix length variations can be carried out. Focal Area 3 - AFM measurements will be used to explore how proximal charged groups affect hydrophobically driven poly-alpha-peptide assembly at surfaces. Interactiorns of single alpha-helical peptides with a hydrophobic tip surface will be evaluated. If HS-CC-K (C-terminal Cys residue) behavior indicates peptide interaction with the AFM tip in an alpha-helical conformation, additional analogues will be investigated (specifically replacing Lys resides ate and g positions with Arg residues (HS-CC-R)). Side chain crosslinks can be introduced to enhance alpha-helix propensity. AFM will also be used to measure the effects of proximal charge on hydrophobic interacLions that lead to coiled-coil dimerization. These experiments will be performed with designed alpha-peptides based on the CC-Di and CC-K series.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jan 12, 2017
- Source ID
- W911NF1610154
Entities
People
- Samuel H. Gellman
Organizations
- Army Contracting Command
- United States Army
- University of Wisconsin–Madison