Examination of pH dependency and orientation differences of membrane spanning alpha helices carrying a single or pair of buried histidine residues.

We have employed the peptide framework of GWALP23 (acetyl-GGALWLALALALALALALWLAGA-amide) to examine the orientation, dynamics and pH dependence of peptides having buried single or pairs of histidine residues. When residue L8 is substituted to yield GWALP23-H, acetyl-GGALWLAHALALALALALWLAGA-amide, the deuterium NMR spectra of H-labeled core alanine residues reveal a helix that occupies a single transmembrane orientation in DLPC, or in DMPC at low pH, yet shows multiple states at higher pH or in bilayers of DOPC. Moreover, a single histidine at position 8 or 16 in the GWALP23 framework is sensitive to pH.

Influence of Lipid Saturation, Hydrophobic Length and Cholesterol on Double-Arginine-Containing Helical Peptides in Bilayer Membranes.

Membrane proteins are essential for many cell processes yet are more difficult to investigate than soluble proteins. Charged residues often contribute significantly to membrane protein function. Model peptides such as GWALP23 (acetyl-GGALW LAL LALALAL ALW LAGA-amide) can be used to characterize the influence of specific residues on transmembrane protein domains.

Control of Transmembrane Helix Dynamics by Interfacial Tryptophan Residues.

Transmembrane protein domains often contain interfacial aromatic residues, which may play a role in the insertion and stability of membrane helices. Residues such as Trp or Tyr, therefore, are often found situated at the lipid-water interface. We have examined the extent to which the precise radial locations of interfacial Trp residues may influence peptide helix orientation and dynamics.

Influence of High pH and Cholesterol on Single Arginine-Containing Transmembrane Peptide Helices.

An essential component of mammalian cells, cholesterol exerts significant influence on the physical properties of the cell membrane and in turn its constituents, including membrane proteins. Although sparse, polar amino acid residues are highly conserved in membrane proteins and play pivotal roles in determining specific structural and functional properties. To improve our understanding of particular polar residues in the membrane environment, we have examined two specific "guest" Arg residues within a well-defined and deuterium-labeled "host" framework provided by the transmembrane helical peptide GWALP23 (acetyl-GGALWLALALALALALALWLAGA-amide).

Ionization Properties of Histidine Residues in the Lipid Bilayer Membrane Environment.

We address the critically important ionization properties of histidine side chains of membrane proteins, when exposed directly to lipid acyl chains within lipid bilayer membranes. The problem is important for addressing general principles that may underlie membrane protein function. To this end, we have employed a favorable host peptide framework provided by GWALP23 (acetyl-GGALW(5)LALALALALALALW(19)LAGA-amide).

Dynamic regulation of lipid-protein interactions.

We review the importance of helix motions for the function of several important categories of membrane proteins and for the properties of several model molecular systems. For voltage-gated potassium or sodium channels, sliding, tilting and/or rotational movements of the S4 helix accompanied by a swapping of cognate side-chain ion-pair interactions regulate the channel gating. In the seven-helix G protein-coupled receptors, exemplified by the rhodopsins, collective helix motions serve to activate the functional signaling.